Astronomy - Black Holes

 

Black Holes

 

A black hole is a region of space-time exhibiting such strong gravitational effects that nothing not even particles and electromagnetic radiation such as light can escape from inside it.

The theory of general relativity predicts that a sufficiently compact mass can deform space-time to form a black hole.

The boundary of the region from which no escape is possible is called the event horizon.

Although the event horizon has an enormous effect on the fate and circumstances of an object crossing it, no locally detectable features appear to be observed.

Objects whose gravitational fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace.

The first modern solution of general relativity that would characterize a black hole was found by Karl Schwarzschild in 1916, although its interpretation as a region of space from which nothing can escape was first published by David Finkelstein in 1958.

Black holes were long considered a mathematical curiosity; it was during the 1960s that theoretical work showed they were a generic prediction of general relativity.

The discovery of neutron stars [ the collapsed core of a large (10–29 solar masses) star] sparked interest in gravitationally collapsed compact objects as a possible astrophysical reality.

Black holes of stellar mass are expected to form when very massive stars collapse at the end of their life cycle.

After a black hole has formed, it can continue to grow by absorbing mass from its surroundings.

By absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses may form.

There is consensus that supermassive black holes exist in the centres of most galaxies.

Despite its invisible interior, the presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as visible light.

Matter that falls onto a black hole can form an external accretion disk heated by friction, forming some of the brightest objects in the universe.

If there are other stars orbiting a black hole, their orbits can be used to determine the black hole's mass and location.

Such observations can be used to exclude possible alternatives such as neutron stars. In this way, astronomers have identified numerous stellar black hole candidates in binary systems, and established that the radio source known as Sagittarius A, at the core of our own Milky Way galaxy, contains a supermassive black hole of about 4.3 million solar masses.

Far away from the black hole, a particle can move in any direction.

Closer to the black hole, space-time starts to deform. There are more paths going towards the black hole than paths moving away.

Inside of the event horizon, all paths bring the particle closer to the center of the black hole. It is no longer possible for the particle to escape.

As predicted by general relativity, the presence of a mass deforms space-time in such a way that the paths taken by particles bend towards the mass.

At the event horizon of a black hole, this deformation becomes so strong that there are no paths that lead away from the black hole.

To a distant observer, clocks near a black hole appear to tick more slowly than those further away from the black hole.

Due to this effect, known as gravitational time dilation, an object falling into a black hole appears to slow as it approaches the event horizon, taking an infinite time to reach it.

At the same time, all processes on this object slow down, from the view point of a fixed outside observer, causing any light emitted by the object to appear redder and dimmer, an effect known as gravitational redshift.

Eventually, the falling object becomes so dim that it can no longer be seen

Astronomy - Telescopes

Telescopes

Lenses and their properties were known well before the invention of the optical telescope; simple lenses made from rock crystal have been known from before recorded history.

1611--The term "telescope" is coined by Prince Frederick Sesi at a reception where Galileo was demonstrating his instruments.

The earliest known working telescopes appeared in 1608 in the Netherlands and are credited to Hans Lippershey and others.

The design of these early refracting telescopes consisted of a convex objective lens and a concave eyepiece. They are constructed this way to not invert the image.

Lippershey's original design had only 3x magnification.

In 1611, Johannes Kepler described how a telescope could be made with a convex objective lens and a convex eyepiece lens and by 1655 astronomers such as Christiaan Huygens were building powerful but unwieldy Keplerian telescopes with compound eyepieces.

Telescopes seem to have been made in the Netherlands in considerable numbers soon after the date of their invention, and rapidly found their way all over Europe.

Keplerian telescope

Isaac Newton is credited with building the first "practical" reflector in 1668 with a design that incorporated a small flat diagonal mirror to reflect the light to an eyepiece mounted on the side of the telescope.

Laurent Cassegrain in 1672 described the design of a reflector with a small convex secondary mirror to reflect light through a central hole in the main mirror.

Newton Reflector

 

Gassegrain Reflector

About the year 1774 William Herschel (then a teacher of music in Bath, England) began to occupy his leisure hours with the construction of reflector telescope mirrors, finally devoted himself entirely to their construction and use in astronomical research.

In 1783, Herschel completed a reflector of approximately 18 inches (46 cm) in diameter and 20 ft. (6.1 m) focal length. He observed the heavens with this telescope for some twenty years, replacing the mirror several times.

In 1789 Herschel finished building his largest reflecting telescope with a mirror of 49 inches (120 cm) and a focal length of 40 ft. (12 m), (commonly known as his 40-foot telescope) at his new home, at Observatory House in Slough.

This telescope was world's largest telescope for over 50 years. However, this large scope was difficult to handle and thus less used than his favourite 18.7-inch reflector.

Essentially all major optical research telescopes since 1900 have been reflectors. A number of 4-metre class (160 inch) telescopes were built on superior higher altitude sites including Hawaii and the Chilean desert in the 1975–1985 era.

The development of the computer-controlled alt-azimuth mount in the 1970s and active optics in the 1980s enabled a new generation of even larger telescopes.

An altazimuth or alt-azimuth mount is a simple two-axis mount for supporting and rotating an instrument about two perpendicular axes – one vertical and the other horizontal.

Rotation about the vertical axis varies the azimuth (compass bearing) of the pointing direction of the instrument. Rotation about the horizontal axis varies the altitude (angle of elevation) of the pointing direction.

John Dobson popularized a simplified altazimuth mount design for Newtonian reflectors because of its ease of construction; Dobson's innovation was to use non-machined parts for the mount that could be found in any hardware store such as plywood, Formica, and plastic plumbing parts combined with modern materials such as nylon or Teflon.

A Newtonian Telescope on a Simple Dobsonian Mount

An equatorial mount is a mount for instruments that compensate the rotation of earth by having one rotational axis parallel to the Earth's axis of rotation. This type of mount is used for astronomical telescopes and cameras.

The advantage of an equatorial mount lies in its ability to allow the instrument attached to it to stay fixed on any object in the sky by driving one axis at a constant speed. Such an arrangement is called a sidereal drive.

A computerised telescope is a telescope with the so-called "GoTofunction". A GoTo-system prevents you from having to locate an object in space yourself. You can always be sure that you focus on the right star or planet.

There is no need to adjust the telescope yourself either, this is done automatically! All in all, this is a great invention, especially for the beginning or amateur astronomer. The GoTofunction enables you to find your way in space, with just a push of a button.

All celestial objects with a temperature above absolute zero emit some form of electromagnetic radiation. In order to study the universe, scientists use several different types of telescopes to detect these different types of emitted radiation in the electromagnetic spectrum. Some of these are gamma ray, x-ray, ultra-violet, regular visible light (optical), as well as infrared telescopes.

An infrared telescope is a telescope that uses infrared light to detect celestial bodies. Infrared light is one of several types of radiation present in the electromagnetic spectrum.

In 1800, William Herschel discovered infrared radiation.

A radio telescope is a specialized antenna and radio receiver used to receive radio waves from astronomical radio sources in the sky.

Radio astronomy studies the radio frequency portion of the electromagnetic spectrum emitted by astronomical objects,

The era of radio telescopes (along with radio astronomy) was born with Karl GutheJansky'sdiscovery of an astronomical radio source in 1931. Many types of telescopes were developed in the 20th century for a wide range of wavelengths from radio to gamma-rays.

The development of space observatories after 1960 allowed access to several bands impossible to observe from the ground, including X-rays and longer wavelength infrared bands.

The 76 metre Lovell, Jodrell Bank

IACT stands for Imaging Atmospheric (or Air) Cherenkov Telescope. It is a device or method to detect very-high-energy gamma-ray photons. There are currently three operating IACT systems: H.E.S.S., MAGIC and VERITAS.

Set to be the world's largest telescope at the highest altitude, the Major Atmospheric Cerenkov Experiment Telescope (MACE) is currently being established at Hanle, Ladakh, India. Also, currently under design is the Cherenkov Telescope Array (CTA).

The SubmillimeterTelescope (SMT), formerly known as the Heinrich Hertz SubmillimeterTelescope, is a submillimeterwavelength radio telescope located on Mount Graham, Arizona. It is a 10-meter-wide parabolic dish inside a building to protect it from bad weather. The telescope's construction was finished in 1993. Along with the 12 Meter Telescope on KittPeak, this telescope is maintained by the Arizona Radio Observatory, a division of Steward Observatory at the University of Arizona.

Ultraviolet astronomy is the observation of electromagnetic radiation at ultraviolet wavelengths between approximately 10 and 320 nanometres; shorter wavelengths—higher energy photons—are studied by X-ray astronomy and gamma ray astronomy.

Light at these wavelengths is absorbed by the Earth's atmosphere, so observations at these wavelengths must be performed from the upper atmosphere or from space.

An X-ray telescope (XRT) is a telescope that is designed to observe remote objects in the X-ray spectrum. In order to get above the Earth's atmosphere, which is opaque to X-rays, X-ray telescopes must be mounted on high altitude rockets, balloons or artificial satellites.

The basic elements of the telescope are the optics, that collects the radiation entering the telescope, and the detector, on which the radiation is collected and measured. A variety of different designs and technologies have been used for these elements.

A solar telescope is a special purpose telescope used to observe the Sun. Solar telescopes usually detect light with wavelengths in, or not far outside, the visible spectrum.

Professional solar observatories may have main optical elements with very long focal lengths and light paths operating in a vacuum or helium to eliminate air motion due to convection inside the telescope.

 

 

Astronomy - Binary Systems

Binary Stars

Since the invention of the telescope, many pairs of double stars have been found.

John Michell was the first to suggest that double stars might be physically attached to each other when he argued in 1767 that the probability that a double star was due to a chance alignment was small.

The term binary was first used in this context by Sir William Herschel in 1802, when he wrote.

"If, on the contrary, two stars should really be situated very near each other, and at the same time so far insulated as not to be materially affected by the attractions of neighbouring stars, they will then compose a separate system, and remain united by the bond of their own mutual gravitation towards each other".

William Herschel began observing double stars in 1779 and soon thereafter published catalogues of about 700 double stars. By 1803, he had observed changes in the relative positions in a number of double stars over the course of 25 years, and concluded that they must be binary systems;

The first orbit of a binary star, however, was not computed until 1827, when Félix Savary computed the orbit of Xi Ursae Majoris.

Since this time, many more double stars have been catalogued and measured. The Washington Double Star Catalogue, a database of visual double stars compiled by the United States Naval Observatory, contains over 100,000 pairs of double stars, including optical doubles as well as binary stars.

A binary system  is an astronomical term referring to two objects in space (usually stars, but also planets, black holes, galaxies or asteroids) which are so close that their gravitational interaction causes them to orbit about a common center of mass called a barycenter.

In a binary system the brightest object is referred to as primary, and the dimmer the secondary.

Two Stars Orbiting Barycentre

More than four-fifths of the single points of light we observe in the night sky are actually two or more stars orbiting together. The most common of the multiple star systems are binary stars, systems of only two stars together. These pairs come in an array of configurations that help scientists to classify stars, and could have impacts on the development of life.

Wide binaries are objects with orbits that keep them a part from one another. They evolve separately and have very little effects on each other.

Close binaries are close to each other and are able to transfer mass from one another. They may also exert a gravitational force on each other.

Visual binaries are two stars separated enough that they can be viewed through a telescope or binoculars. The relative brightness of the two stars is an important factor, as glare from a bright star may make it difficult to detect the presence of a fainter component.

Eclipsing binaries are where the object's orbits are at an angle that when one passes in front of the other it causes an eclipse or transit, as seen from Earth.

Astrometric binaries are objects that seem to move around nothing as their companion object cannot be identified, it can only be inferred.

The companion object may not be bright enough or may be hidden in the glare from the primary object.

Spectroscopic binaries

Sometimes, the only evidence of a binary star comes from the Doppler effect on its emitted light. In these cases, the binary consists of a pair of stars where the spectral lines in the light emitted from each star shifts first towards the blue, then towards the red, as each moves first towards us, and then away from us, during its motion about their common center of mass, with the period of their common orbit.

While it is not impossible that some binaries might be created through gravitational capture between two single stars, given the very low likelihood of such an event (three objects are actually required, as conservation of energy rules out a single gravitating body capturing another) and the high number of binaries, this cannot be the primary formation process.

Also, the observation of binaries consisting of pre main-sequence stars, supports the theory that binaries are already formed during star formation.

Fragmentation of the molecular cloud during the formation of protostarsis an acceptable explanation for the formation of a binary or multiple star system.

Astronomy - Soviet Space Programme

Soviet Space Programme

The theory of space exploration had a solid basis in the Russian Empire before the First World War with the writings of Konstantin Tsiolkovsky (1857-1935), who published pioneering papers in the late 19th and early 20th centuries and in 1929 introduced the concept of the multistage rocket.

Practical aspects built on early experiments carried out by members of the reactive propulsion study group, GIRD (founded in 1931).

Konstantin Tsiolkovsky

On August 18, 1933, GIRD launched the first Soviet liquid-fuelled rocket Gird-09, and on November 25, 1933, the first hybrid-fuelled rocket GIRD-X.

In 1940-41 another advance in the reactive propulsion field took place: the development and serial production of the Katyusha multiple rocket launcher.

The Russian program greatly benefited from captured German records and scientists, in particular drawings obtained from the V-2 production sites.

Gird-09

GIRD-X

They built a replica of the V-2 called the R-1, although the weight of Soviet nuclear warheads required a more powerful booster.

Sergey Korolev's OKB-1 design bureau was dedicated to the liquid-fuelled cryogenic rockets he had been experimenting with in the late 1930s.

Ultimately, this work resulted in the design of the R-7 Semyorka intercontinental ballistic missile (ICBM) which was successfully tested in August 1957.

Sergey Korolev

R-7

The Soviet space program was tied to the USSR's Five-Year Plans and from the start was reliant on support from the Soviet military.

The first Soviet rocket with animals aboard launched in July 1951; the two dogs were recovered alive after reaching 101 km in altitude. Two months ahead of America's first such achievement, this and subsequent flights gave the Soviets valuable experience with space medicine.

Because of its global range and large payload of approximately five tons, the reliable R-7 was not only effective as a strategic delivery system for nuclear warheads, but also as an excellent basis for a space vehicle.

The United States' announcement in July 1955 of its plan to launch a satellite during the International Geophysical Year

Persuading Soviet leader Nikita Khrushchev to support plans in January 1956, in order to surpass the Americans.

Plans were approved for Earth-orbiting satellites (Sputnik) to gain knowledge of space, and four unmanned military reconnaissance satellites, Zenit.

Further planned developments called for a manned Earth orbit flight by 1964 and an unmanned lunar mission at an earlier date.

Sputnik

After the first Sputnik proved to be a successful propaganda coup, Korolev now known publicly only as the anonymous "Chief Designer of Rocket-Space Systems" was charged to accelerate the manned program, the design of which was combined with the Zenit program to produce the Vostok spacecraft.

In the early 1960s the Russian program under Korolev created substantial plans for manned trips to Mars as early as 1968 to 1970.

Vostok

The Soviet space program was secondary in military funding to the Strategic Rocket Forces' ICBMs.

While the West believed that Khrushchev personally ordered each new space mission for propaganda purposes.

Khruschev emphasized missiles rather than space exploration and was not very interested in competing with Apollo.

While the government and the Communist Party used the program's successes as propaganda tools after they occurred, systematic plans for missions based on political reasons were rare, one exception being Valentina Tereshkova, the first woman in space, on Vostok 6 in 1963.

Valentina Tereshkova

More than three years after the United States declared its intentions the Soviet Union finally decided to compete for the moon.

It set the goal of a lunar landing in 1967 the 50th anniversary of the October Revolution or 1968. At one stage in the early 1960s the Soviet space program was actively developing 30 projects for launchers and spacecraft.

With the fall of Krushchev in 1964, Korolev was given complete control of the

Soyuz 1 was a manned spaceflight of the Soviet space program. Launched into orbit on 23 April 1967 carrying cosmonaut Colonel Vladimir Komarov, Soyuz 1 was the first crewed flight of the Soyuz spacecraft.

The mission plan was complex, involving a rendezvous with Soyuz 2 and an exchange of crew members before returning to Earth. However, the launch of Soyuz 2 was called off due to thunderstorms.

manned space program.

The flight was plagued with technical issues, and Komarov was killed when the descent module crashed into the ground due to a parachute failure.

This was the first in-flight fatality in the history of spaceflight.

Soyuz

Korolev died in January 1966 following a routine operation Kerim Kerimov, who was formerly an architect of Vostok 1, was appointed Chairman of the State Commission on Piloted Flights and headed it for the next 25 years (1966–1991).

He supervised every stage of development and operation of both manned space complexes as well as unmanned interplanetary stations for the former Soviet Union.

One of Kerimov's greatest achievements was the launch of Mir in 1986.

Kerim Kerimov

Mir

The Soviets were beaten in sending the first manned flight around the Moon in 1968 by Apollo 8.

With the collapse of the Soviet Union, Russia and Ukraine inherited the program.

Russia created the Russian Aviation and Space Agency, now known as the Roscosmos State Corporation, while Ukraine created the National Space Agency of Ukraine (NSAU).

The Soviet space program pioneered many aspects of space exploration

1957: First intercontinental ballistic missile and orbital launch vehicle, the R-7 Semyorka

1957: First satellite, Sputnik 1

1957: First animal in Earth orbit, the dog Laika on Sputnik 2

1959: First rocket ignition in Earth orbit, first man-made object to escape Earth's gravity, Luna 1

1959: First data communications, or telemetry, to and from outer space, Luna 1.

1959: First man-made object to pass near the Moon, first man-made object in Heliocentric orbit, Luna 1

1959: First probe to impact the Moon, Luna 2

1959: First images of the moon's far side, Luna 3

1960: First animals to safely return from Earth orbit, the dogs Belka and Strelka on Sputnik 5.

1961: First probe launched to Venus, Venera 1

1961: First person in space (International definition) and in Earth orbit, Yuri Gagarin on Vostok 1, Vostok programme

1961: First person to spend over 24 hours in space Gherman Titov, Vostok 2 (also first person to sleep in space).

1962: First dual manned spaceflight, Vostok 3 and Vostok 4

1962: First probe launched to Mars, Mars 1

1963: First woman in space, Valentina Tereshkova, Vostok 6

1964: First multi-person crew (3), Voskhod 1

1965: First extra-vehicular activity (EVA), by Aleksei Leonov, Voskhod 2

1965: First probe to hit another planet of the Solar system (Venus), Venera 3

1966: First probe to make a soft landing on and transmit from the surface of the moon, Luna 9

1966: First probe in lunar orbit, Luna 10

1967: First unmanned rendezvous and docking, Cosmos 186/Cosmos 188.

1968: First living beings to reach the Moon (circumlunar flights) and return unharmed to Earth, Russian tortoises on Zond 5

1969: First docking between two manned craft in Earth orbit and exchange of crews, Soyuz 4 and Soyuz 5

1970: First soil samples automatically extracted and returned to Earth from another celestial body, Luna 16

1970: First robotic space rover, Lunokhod 1 on the Moon.

1970: First data received from the surface of another planet of the Solar system (Venus), Venera 7

1971: First space station, Salyut 1

1971: First probe to impact the surface of Mars, Mars 2

1971: First probe to land on Mars, Mars 3

1975: First probe to orbit Venus, to make soft landing on Venus, first photos from surface of Venus, Venera 9

1980: First Hispanic and Black person in space, Arnaldo Tamayo Méndez on    Soyuz 38

1984: First woman to walk in space, Svetlana Savitskaya (Salyut 7 space station)

1986: First crew to visit two separate space stations (Mir and Salyut 7)

1986: First probes to deploy robotic balloons into Venus atmosphere and to return pictures of a comet during close flyby Vega 1, Vega 2

1986: First permanently manned space station, Mir, 1986–2001, with permanent presence on board (1989–1999)

1987: First crew to spend over one year in space, Vladimir Titov and Musa Manarov on board of Soyuz TM-4 – Mir

The Soviet space program has experienced a number of fatal incidents and failures.

The so-called Nedelin catastrophe in 1960 was a disastrous explosion of a fuelled rocket being tested on launchpad, killing many technical personnel, aerospace engineers, and technicians working on the project at the time of the explosion.

The first official cosmonaut fatality during training occurred on March 23, 1961, when Valentin Bondarenko died in a fire within a low pressure, high oxygen atmosphere.

The Voskhod program was cancelled after two manned flights owing to the change of Soviet leadership and nearly fatal 'close calls' during the second mission. Had the planned further flights gone ahead they could have given the Soviet space program further 'firsts' including a long duration flight of 20 days, a spacewalk by a woman and an untethered spacewalk.

The deaths of Korolev, Komarov (in the Soyuz 1 crash) and first human in space Gagarin (on a routine fighter jet mission) within two years of each other understandably had substantial negative impact on the Soviet program.

The Soviets continued striving for the first lunar mission with the huge N-1 rocket, which exploded on each of four unmanned tests shortly after launch. The Americans won the race to land men on the moon with Apollo 11 on July 20, 1969.

In 1971, the Soyuz 11 mission resulted in the deaths of three cosmonauts when the crew capsule depressurized during preparations for re-entry.

This accident resulted in the only human deaths to occur in space (as opposed to high atmosphere).The crew members aboard Soyuz 11 were Vladislav Volkov, Georgi Dobrovolski, and Viktor Patsayev.

On April 5, 1975, Soyuz 7K-T No.39, the second stage of a Soyuz rocket carrying 2 cosmonauts to the Salyut 4 space station malfunctioned, resulting in the first manned launch abort. The cosmonauts were carried several thousand miles downrange and became worried that they would land in China, which the Soviet Union was then having difficult relations with. The capsule hit a mountain, sliding down a slope and almost slid off a cliff; fortunately the parachute lines snagged on trees and kept this from happening. As it was, the two suffered severe injuries and the commander, Lazerev, never flew again.

On March 18, 1980, a Vostok rocket exploded on its launch pad during a fuelling operation, killing 48 people.

In August 1981, Kosmos434, which had been launched in 1971, was about to re-enter. To allay fears that the spacecraft carried nuclear materials, a spokesperson from the Ministry of Foreign Affairs of the USSR assured the Australian government on August 26, 1981, that the satellite was "an experimental lunar cabin". This was one of the first admissions by the Soviet Union that it had ever engaged in a manned lunar spaceflight program.

In September 1983, a Soyuz rocket being launched to carry cosmonauts to the Salyut 7 space station exploded on the pad, causing the Soyuz capsule's abort system to engage, saving the two cosmonauts on board.

In addition to these, there have been several unconfirmed accounts of Lost Cosmonauts whose deaths were allegedly covered up by the Soviet Union.

Astronomy - Comets and Asteroids

The word comet derives from the Old English cometa from the Latin comēta or comētēs. That, in turn, is a latinisation of the Greek κομήτης("wearing long hair"), and the Oxford English Dictionary notes that the term (ἀστὴρ) κομήτηςalready meant "long-haired star, comet" in Greek and was used to mean "the tail of a comet".

The astronomical symbol for comets is ☄, consisting of a small disc with three hair like extensions.

Comets have been observed and recorded since ancient times by many cultures.

From ancient sources, such as Chinese oracle bones, it is known that their appearances have been noticed by humans for millennia.

Until the sixteenth century, comets were usually considered bad omens of deaths of kings or noble men, or coming catastrophes, or even interpreted as attacks by heavenly beings against terrestrial inhabitants.

The depiction of comets in popular culture is firmly rooted in the long Western tradition of seeing comets as harbingers of doom and as omens of world-altering change.

Halley's Comet alone has caused a slew of sensationalist publications of all sorts at each of its reappearances.

Bayer Tapestry Halleys Comet

Isaac Newton, in his Principia Mathematica of 1687, proved that an object moving under the influence of gravity must trace out an orbit shaped like one of the conic sections, and he demonstrated how to fit a comet's path through the sky to a parabolic orbit, using the comet of 1680 as an example.

Great Comet 1680

In 1705, Edmond Halley (1656–1742) applied Newton's method to twenty-three cometary apparitions that had occurred between 1337 and 1698. He noted that three of these, the comets of 1531, 1607, and 1682, had very similar orbital elements.

Confident that these three apparitions had been three appearances of the same comet, he predicted that it would appear again in 1758–9.

When the comet returned as predicted, it became known as Halley's Comet. It will next appear in 2061.

A comet is an icy small Solar System body that, when passing close to the Sun, warms and begins to evolve gasses, a process called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail.

These phenomena are due to the effects of solar radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred metres to tens of kilometres across.

Cometary nuclei are composed of an amalgamation of rock, dust, water ice, and frozen gases such as carbon dioxide, carbon monoxide, methane, and ammonia. As such, they are popularly described as "dirty snowballs" after Fred Lawrence Whipple's (Professor of Astronomy Harvard College) model.

However, some comets may have a higher dust content, leading them to be called "icy dirtballs".

The surface of the nucleus is generally dry, dusty or rocky, suggesting that the ices are hidden beneath a surface crust several metres thick.

In addition to the gases already mentioned, the nuclei contain a variety of organic compounds, which may include methanol, hydrogen cyanide, formaldehyde, ethanol, and ethane and perhaps more complex molecules such as long-chain hydrocarbons and amino acids.

In 2009, it was confirmed that the amino acid glycine had been found in the comet dust recovered by NASA's Stardust mission.

In August 2011, a report, based on NASA studies of meteorites found on Earth, was published suggesting DNA and RNA components (adenine, guanine, and related organic molecules) may have been formed on asteroids and comets.

Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years.

Short-period comets originate in the Kuiper belt or its associated scattered disc, which lie beyond the orbit of Neptune. Long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star.

 

 

Long-period comets are set in motion towards the Sun from the Oort cloud by gravitational perturbations caused by passing stars and the galactic tide.

Hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space.

Asteroids

The first asteroid to be discovered, Ceres, was found in 1801 by Giuseppe Piazzi, director of the observatory of Palermo in Sicily, and was originally considered to be a new planet.

This was followed by the discovery of other similar bodies, which, with the equipment of the time, appeared to be points of light, like stars, showing little or no planetary disc, though readily distinguishable from stars due to their apparent motions.

This prompted the astronomer Sir William Herschel to propose the term "asteroid", coined in Greek as ἀστεροειδής, or asteroeidēs, meaning 'star-like, star-shaped', and derived from the Ancient Greek ἀστήρastēr'star, planet'.

In the early second half of the nineteenth century, the terms "asteroid" and "planet" (not always qualified as "minor") were still used interchangeably.

Asteroids are minor planets, especially those of the inner Solar System. The larger ones have also been called planetoids. These terms have historically been applied to any astronomical object orbiting the Sun that did not show the disc of a planet and was not observed to have the characteristics of an active comet.

There are millions of asteroids, many thought to be the shattered remnants of planetesimals, bodies within the young Sun's solar nebula that never grew large enough to become planets.

The large majority of known asteroids orbit in the asteroid belt between the orbits of Mars and Jupiter, or are co-orbital with Jupiter (the Jupiter trojans).

However, other orbital families exist with significant populations, including the near-Earth objects.

Asteroid Belt

Individual asteroids are classified by their characteristic spectra, with the majority falling into three main groups:

C-type, M-type, and S-type.

C-type asteroids are carbonaceous asteroids their composition includes a large amount of carbon, in addition to rocks and minerals. They are the most common variety, forming around 75% of known asteroids

M-type asteroids are asteroids of partially known composition; they are moderately bright. Some, but not all, are made of nickel–iron, either pure or mixed with small amounts of stone.

S-type asteroids, or siliceous asteroids, are of a stony composition Approximately 17% of asteroids are of this type, making it the second most common after the C-type.

It is thought that planetesimals in the asteroid belt evolved much like the rest of the solar nebula until Jupiter neared its current mass, at which point excitation from orbital resonances with Jupiter ejected over 99% of planetesimals in the belt.

Most of this ancient space rubble can be found orbiting the sun between Mars and Jupiter within the main asteroid belt.

Asteroids range in size from Vesta - the largest at about 329 miles (530 kilometres) in diameter  to bodies that are less than 33 feet (10 meters) across. 

The total mass of all the asteroids combined is less than that of Earth's Moon.

Most asteroids are irregularly shaped, though a few are nearly spherical, and they are often pitted or cratered. As they revolve around the sun in elliptical orbits, the asteroids also rotate, sometimes quite erratically, tumbling as they go.

More than 150 asteroids are known to have a small companion moon (some have two moons). There are also binary (double) asteroids, in which two rocky bodies of roughly equal size orbit each other, as well as triple asteroid systems.

Several missions have flown by and observed asteroids. The Galileo spacecraft flew by asteroids Gasprain 1991 and Ida in 1993; the Near-Earth Asteroid Rendezvous (NEAR-Shoemaker) mission studied asteroids Mathilde and Eros; and the Rosetta mission encountered Steins in 2008 and Lutetia in 2010.

Deep Space 1 and Stardust both had close encounters with asteroids.

In 2005, the Japanese spacecraft Hayabusa landed on the near-Earth asteroid Itokawa and attempted to collect samples. On June 3, 2010, Hayabusa successfully returned to Earth a small amount of asteroid dust now being studied by scientists.

NASA's Dawn spacecraft, launched in 2007, orbited and explored asteroid Vesta for over a year. Once it left in September 2012, it headed towards dwarf planet Ceres, with a planned arrival of 2015.

Vesta and Ceres are two of the largest surviving protoplanet bodies that almost became planets. By studying them with the same complement of instruments on board the same spacecraft, scientists will be able to compare and contrast the different evolutionary path each object took to help understand the early solar system overall.

Astronomy - The Moon

The Moon

By Margaret Grove

The moon is the earths only natural satellite and is the second brightest object in the sky after the sun. It is also the only object other than earth to have been stepped on by human beings.

We can clearly see, particularly with binoculars and telescopes, many dark patches on the moon’s surface. Ancient astronomers thought these were filled with water and so they are called ‘mare’ Latin for sea. We now know that they are solidified pools of lava.

The moon derives its name from the Romans, Luna and the Greek, Selene and its rhythm has been part of time keeping for thousands of years. Its synchronous rotation means that the far side of the moon was relatively unknown until a probe photographed it in 1959.

Manned Apollo orbits in the late 60s and 70s increased our knowledge revealing a densely crated surface with more highlands and fewer of the dark ‘seas’ than the near side. This indicates a thicker crust where lava could not so easily rise to the surface. 

There is no atmosphere and no oceans but ice left by crashed comets has been found. Other parts of the moon’s surface are very mountainous and their peaks are nearly as high as Everest. The moon is also dotted with craters made by meteorites crashing into it around 4 billion years ago.

It is generally accepted now by scientists that the moon is now some 4.5 billion years old. The earth was still in its molten state when it was hit by possibly an asteroid and it was gravity that drew debris together to form the moon.

This debris must have been at least 14,000 miles away from earth, any closer and it would have crashed back to earth and the moon would not exist. The earth was spinning much faster then so making days and nights much shorter.

 

 

It took time for the earth and moon to cool down and become the perfect companions they are today.

The moon orbits the earth on an elliptical path which means there are times when the moon is closer to the earth, Perigee, and rotates faster and times when it is further away, Apogee where it rotates slower. The difference between these two points is about the width of 4 earths.

The earth and the moon have their own centre of gravity but there is a common centre of gravity called the Barycentre. This point is nearer to the circumference of the earth than the centre itself and moves according to the movement of both earth and moon.

Relative to the earth the moon makes one rotation around its axis every 29 and half days on average. This is the same time it takes for the moon to complete one revolution around the earth. This is no coincidence. In the past when the moon was nearer to the earth it rotated faster but one of the effects of the earth’s gravity over millions of years has been to slow down the rotation until the moon has become completely synchronised with earth.

The 29-and-a-half-day orbit is called Lunation or Lunar month. This is the exact time that is recorded between one new moon and the next. The precise measurement is 29 days 12 hours 44 mins. and 2.8 secs. This measurement is an average and not a constant and reflects monthly variations that occur over a long period of time.

Phases of the Moon.

The moon changes its appearance on a very regular monthly pattern. These phases happen because the moon orbits the earth once every 27.3 days. When the moon passes between the sun and the earth we see very little of the sunlight that is reflected from it giving us the new moon. Fourteen days later the moon is on the far side of the earth from the sun and we see it completely illuminated giving us the full moon.

A gradual increase in the visual is called waxing first appearing as a waxing crescent, next the first quarter then to a waxing gibbous increasing to the full moon. The visual decreases to a waning gibbous, the last quarter and waning crescent where it disappears to become the new moon which we cannot see.

The first and last quarter moons mark the halfway point between the full and new moon. It is interesting to note that there is slightly more light reflected from the waning crescent moon than the waxing crescent moon but between the full moon and the quarter phases the waxing period is brighter than the waning period.

The full moon is the brightest as the sunlight strikes the full face of the moon and is reflected back to earth. Another factor has been found increasing the intensity of the moons reflected light while examining moon dust brought back from the Apollo expeditions. It has revealed the role of tiny particles that cling to the surface of Luna sand to amplify rays of light, a condition that has been described as ‘coherent backscattering’.

Under certain conditions such as a full moon the reflection intensifies producing more visible light than during other phases.

The moon rises and sets at different times every day because the civil calendar is based on the solar time table and not the lunar. On average, the moon rise and the moon set are about one hour later each succeeding day, but the time changes considerably from one location to another. Both longitude and latitude have an effect on this change. More northern latitudes being affected the most.

The lunar phase cycle of 29.5 days is longer than the orbital period of the moon, this is because during the moons orbit around the earth it is also moving around the sun and we have to wait a little longer to see the same phase in the sky.

Size of the Moon

Any change in size of the moon is an illusion and only changes slightly when the moon is nearer to the earth on its elliptical path. When the moon is nearer to the horizon it appears to be larger than when it is above [Zenith]. The eye is tricked into measuring the moon against the nearby objects e.g. Buildings, trees and hills etc. This gives the impression of an increased size of the moon.

The Tides

The moon is our nearest celestial neighbour an exerts a constant influence through gravitational attraction. This gravitational attraction is one ten millionth of the gravitational force of the earth. Lunar gravity does not work alone in influencing our tides. They are also influenced by the centrifugal force of the earths spin and gravitational attraction of the sun.

The suns gravitational pull is much greater than that of the moon but because the sun is much further away from earth the moons gravitational pull remains supreme which in turn gives the moon a much greater influence on our tides.

The gravitational force of the moon is tugging upwards on the water while the gravitational force of the earth, which is far stronger, is pulling down at the same time. Instead, the water rises with the tides because of the net balance of the forces i.e. The earth pulling in and the moon pulling out, which averages more in favour of the moon. It does not happen in a perpendicular direction, however, but shows up where the external influence has a greater effect, from side to side.

Spring Tides

During new and full moons, the gravitational force of the sun is in line combining to produce the highest tides.

Neap Tides

During the quarter moons the gravitational forces of the sun and the moon are at right angles partially offsetting each other to produce the lowest tides.

Lunar Eclipse

There are three types of lunar eclipse, a total, a penumbral and a partial eclipse.

The shadow cast during an eclipse has two components, a darker central area [umbra] and a lighter area [the penumbra].

 

Total Lunar Eclipse

The moon passes completely through the main shadow of the earth. The dark shadow cast by the earth does not completely obscure the moon but changes its colour to a deep copper tone. This colour is created by the filtering effect of the earth’s atmosphere which removes all but red wave lengths of red sunlight.

The colour of the shadow can vary due to factors like the atmosphere, weather conditions and volcanic dust. This spectacle can last for around three hours because the moon and earth are moving slowly in relation to one another and the shadow cast by the earth is so large.

Solar activity can also have an effect on a total eclipse particularly the activity of sunspots and the relative distance between the moon and the sun. The 11-year cycle of solar activity is also known to affect the brightness of an eclipse with the moon appearing dimmer when solar activity is low.

Penumbral Eclipse

This is a partial eclipse that can last around 1 hour when the moon only passes through the secondary shadow of the earth. During the penumbral eclipse, the moons light is dimmed but does not go completely dark as the shadow is not deep enough to block out all the suns light.

Partial Eclipse

The moon enters the secondary shadow then passes through part of the umbra or main shadow. This partial eclipse does not produce the reddish colour of a total eclipse as the secondary shadow is not deep enough to highlight the reflected light from the earth.

Solar Eclipse

When the moon is directly between the earth and the sun it blocks out the sun’s rays.

If the moon is in perigee then we see the wonderful spectacle of a total solar eclipse. If the moon however is at its farthest point, Apogee, away from earth then we have an annular eclipse which shows a ring of sunlight around the edge. If the moon does not take the direct approach across the sun then a dark blob will appear on the edge of the sun giving us a partial eclipse.

Interesting Points.

1] A solar eclipse only occurs 2 weeks after or 2 weeks before a total lunar eclipse.

2] Full moons are the only time lunar eclipses occur.

3] Lunar eclipses can last for a maximum of 3 hours 40 mins.

4] New moons the only time solar eclipses occur.

5] A total solar eclipse can last a maximum 7 mins. and 40 secs. timed from the equator. An annular eclipse can last for 12 mins and 24 secs at most.

A solar eclipse happens at least twice a year but never more than five.

6] A lunar eclipse can never happen more than three times a year.

7] A lunar eclipse is visible over an entire hemisphere where as a solar eclipse is visible in a narrow path that is a maximum of 167miles wide.

8] At any specific geographical location on the globe a total solar eclipse can occur only once every 360 years on average.

9] A solar and Luna eclipse go together in pairs. A solar eclipse is always followed or preceded by a Luna eclipse within an interval of 14 days.

10] The characteristics of one eclipse is repeated every 18 years, one day and eight hours with some minor variations. This long-term cycle is called the Saros cycle.

 

Rare Moon Effects

 

 

Earthshine

The light from the sun reflects off the earth’s surface. When this reflected light from the earth produces visible light on the moon it is referred to as earthshine. When the waxing crescent moon is only a few days old light reflected back from earth can illuminate the full surface of the moon.

Optical Effects

The moon can produce some optical effects when combined with the right atmospheric conditions. Just as light from the sun is refracted through water droplets so the light from the moon can produce the same effect but the colours are less intense. This is a moonbow or Luna rainbow. When moisture is high in the atmosphere ice crystals are formed. If the moon is in the right position it can form a halo or ring around itself.

 

 

Moon Dogs or Mock Moons.

These are also produced by the interaction of moonlight and moisture in the atmosphere. With the right combination of humidity and angle, the observer may see bright circular spots on the halo itself caused by the refraction of moonlight through hexagonal shaped crystals. The name for this is parselene.

Rare Moons

Blue moons.

 A Blue moon is the second of two moons that occur in the same month. It can never happen in February. A blue moon occurs approximately 7 times every 19 years and will next appear January 31st and March 31st 2018 then October 31st 2020.

 

 

 

 

Interesting Points

1] Happens once every 2.7 years

2] 7 Times every 19 yrs.

3] Once every 33 months.

4] Average of 37 every century.

5] About the rarest of all blue moons is the year with two.

6] Once every 100 yrs. a full moon will fall on a leap year, Feb 29th. Last time this happened was 1972 and will occur next in 2048, followed by 2132, 2216 and 2376.

A leap year with no full moon in Feb last occurred in 1608 and the next will be in 2572.

7] The term Blue moon was created by astrologists and not astronomers.

Black Moon

Just as rare as the Blue moon is the Black moon. This is the absence of a new moon in the month. This will next appear in February 2018, 2037, 2067 and 2094

The term was once again created by astrologists and not astronomers.

 

Snow moon

February full moon is traditionally called the Snow moon.

Harvest Moon

The full moon that is nearest to the autumn equinox

Super moon

This apparent increase in size is due to the moon being in perigee.

Moon Calendars

There are too many to identify here as they differ all over the world. There are names for every month of the year and some depending on religion.

Lagrange Points.

The gravitation of two orbiting bodies produce a unique condition. As in the case of the earth orbiting the sun, 5 specific points in the orbital patterns have the effect of cancelling the gravitational and centrifugal pull on the two bodies. These points are called the Lagrange points after the discovery in 1772 by a French mathematician of the same name. Lagrange points are important spots as they are able to support space stations, spacecraft or permanent colonies in stable orbits without the need for constant refuelling.

The Lagrange points in the earth/moon system are also affected by additional forces from the sun. In order to be unaffected objects would have to be placed in an elliptical orbit.

Unpiloted Moon Exploration

Luna 1 USSR. Landed on Luna surface.1959

Ranger 7 USA. First pre-impact photo 1964

Ranger 8 USA. Transmitted photos. 1965.

Luna 9 USSR. Landed. Transmitted photos. 1966

Surveyor 1 USA. Landed First coloured photos. 1966

Luna 13 USSR. Landed first soil sample 1966.

Explorer 35 USA. Orbited. Magnetic fields. 1966

Surveyor 5 and 7 USA. Landed. Soil tests and photos. 1967.

 

Apollo Programme.

Started in 1968 USA with Apollo 7. Making orbital tests around the earth.

Apollo 8 1968. First flight to orbit the moon.

Apollo 9 1969. Orbital tests around the earth. First flight of complete Apollo spacecraft.

Apollo 10 1969. Orbital tests and partial descent.

APOLLO 11 1969. LANDING AND FIRST MOON WALK. Armstrong.

Apollo 12 1969. Landing and surface exploration.

Apollo 13 1970. Flyby. Mission aborted in third day.

Apollo 14 1971. Landing and surface exploration.

Apollo 15 1971. First use of Luna rover. First continuous cover TV programme broadcast of moon walk and extensive scientific study of Luna surface.

Apollo 16 1972. Landing and surface exploration.

Apollo 17 1972. Landing. First geological study of Luna surface.

Moon Rocks

Scientists have discovered many interesting features about the composition and origin of the moon from these rocks, most of them formed by cooling lava. Some rocks are similar to Basalt which is found on earth. Samples were collected in low areas that are observed as Maria from the earth. Rocks from the higher regions of the moon are Gabbro and Norite, similar to rocks of the same names on earth. Although some rocks have some characteristics similar to earth rocks they are recognisably different as they were found not to contain any water.The presence of water has a noticeable effect on minerals in the rocks.

Moon rocks also exhibit crystals of metallic iron because of the lack of free oxygen. Material on the surface of the moon is referred to as regolith or Luna soil but has no organic content. Luna soil forms a layer from 3 to 60 feet deep on the surface. It was created over billions of years by the continuous bombardment of meteorites. Larger meteorites caused visible craters that can be seen from earth. Smaller, virtually invisible craters are formed by particles of cosmic dust. Moon rocks are still being investigated as we speak.

Over the last few years water has been found on the moon which is frozen and trapped in the craters at the Luna poles. Water that has come from the crashing of comets into the moon over time.

 

 

Now there is a renewed interest in the moon as scientist are wanting to rethink the possibilities of a return with the idea of building a permanent station using the moons resources. Water that could be turned in to rocket fuel for the purpose of refuelling space craft.

Rockets could be sent deeper into space from the moon thus saving on the enormous amount of fuel [two and half thousand tonnes] it takes to escape the earth’s gravity.

Another idea is to place solar panels on the moon to harness the energy from the sun. The sunlight on the moon is predictable. The energy would be converted into electricity and transmitted down to earth. The amount would satisfy global demand. The cost would be no more than the big oil companies spend over 2 yrs. in the production of oil and gas from the ground. Around £2 billion.

Do We Need the Moon?

The moon is moving away from earth at a rate of 3.78 cm per year. This has been repeated from birth and will continue for the next 4 to 5 billion years.

At the time of its birth both the earth and moon were in a molten state. The moon would have been much closer to earth making it appear very large and would be spinning faster giving us a five-hour day. Even when it had moved away sufficiently and had cooled down enough for the oceans to form, the tides were pulled much higher covering most of the low-lying land. It was a very different place it is today. The pull of the moon was slowing the spin of the earth and continues to do that to this day using the friction between the ocean bulge and the ocean floor.

We only know the 24-hour day due to the length of time we have evolved on earth. All this is due to our moon.

How Do We Know?

Apollo 15 astronauts placed a retroreflector unit packed with small mirrors on the moon.

In New Mexico, a large telescope at Apache point has been firing a series [millions] of laser beams at the units. The response is, one or two photons have been reflected back to earth the distance of which can be measured accurately. This has been a continuous process for the past 40 years and their findings confirm the figure of 3.78 cm is correct.

If it Continues to Move Away, Does it Matter?

As it continues to recede it will look smaller and in turn we will lose one of the world’s greatest spectacles that of a total solar eclipse. The earths spin is slowing down and the days will get longer. When the moon has receded by just 10%, another 24,000 miles, we cannot expect the sun to rise for about 20 hours making the days and nights much longer.

Eventually things will get worse and the stability of our earth will be affected.

The 23 de tilt of our earth give us our seasons. Our animals and plant life rely on them. With further drifting of the moon away from us the angle of the tilt will change over time and cause the earth to wobble. Our earth may also become very wet and if the earth tipped over on to its side for 3 months a year the poles would be under unrelenting sunshine so melting the ice caps. Sea levels would rise 60 meters. Every coastal city in the world would be gone and inland areas that survived would be transformed.

We would have a very dark and cold freezing winter. Over the summer the sun is high in the sky and temperatures soar. Then the pattern is repeated. We as humans could probably survive but other life forms would probably not. Animals could not evolve fast enough to cope with the extremes.

It will take about a billion years before the earth will tip over so we are not in any immediate danger!!

We are indeed enjoying the most stable time of life as we know it, and this knowledge should make us appreciate how fragile the balance is between the Earth and her moon and the Sun.

 

 

Astronomy - The Earth

The Earth

Equatorial Diameter: 12,756 km

Polar Diameter: 12,714 km

Mass: 5.97 x 10^24 kg

Moons: 1 (The Moon) and 2 co-orbital satellites

Orbit Distance: 149,598,262 km 1 Astronomical Unit

Orbit Period: 365.24 days

Surface Temperature:  -88 to 58°C

Earth is the third planet from the Sun and is the largest of the terrestrial planets.

The Earth is the only planet in our solar system not to be named after a Greek or Roman deity.

May have derived from old English word Ertha meaning ground or land.

The Earth is thought to have formed from the solar nebula, the disc-shaped cloud of gas and dust left over from the Sun's formation.

The currently accepted method by which the planets formed is accretion, in which the planets began as dust grains in orbit around the central protostar.

Through direct contact, these grains formed into clumps, which in turn collided to form larger bodies.

These gradually increased through further collisions, growing at the rate of centimetres per year over the course of the next few million years.

Protoplanetary Disk

The first facts about the Earth were worked out by the Ancient Greeks.

A good estimate of the Earth's size was made by Eratosthenes (276 BC–194 BC), using trigonometry.

The first estimate of the Earth's age based on evidence was by Benoît de Maillet(1656–1738), a French diplomat, philosopher and naturalist.

He thought the Earth must have developed by slow, natural forces.

In the last quarter of the 19th century there was a long-running debate on the age of the Earth. In Charles Lyell's Principles of Geology (1830–33), he showed that the Earth had changed slowly, and that what we see is the result of gradual changes.

This clearly meant that the Earth was ancient, though Lyell did not try to work out how old.

In 1896 Henri Becquerel discovered radioactivity, he shared the Nobel Prize in Physics with Pierre and Marie Curie

Eventually, it was realized that radioactivity was a major source of heat inside the Earth.

In 1921 came the first modern estimate, using radiometric dating. It was based on uranium-lead dating, the rate of decay of uranium to lead in the crust of the Earth, by Henry Norris Russell. He came up with 2 to 8 billion years.

In 1949, H.E. Suess estimated 4 to 5 billion years, based on a whole array of radioactive isotopes.

This is close to the time we estimate today, which has been refined further to about 4,560 million years.

Many societies assumed the Earth had always been as it is now.

Some religions raised the question of its age: the Hindu religion got closest to the present-day scientific estimate. Some Christians and Jews believe the Genesis creation narrative is literally true, which would mean that the Earth was created between 5000 and 10,000 years ago. However, these days most people think such questions are best answered by scientific methods.

The Earth was once believed to be the centre of the universe.

Due to the apparent movements of the Sun and planets in relation to their viewpoint, ancient scientists insisted that the Earth remained static, whilst other celestial bodies travelled in circular orbits around it.

Eventually, the view that the Sun was at the centre of the universe was postulated by Copernicus, though this is also not the case.

The Earth is the densest planet in the Solar System.

Earth is mostly iron, oxygen and silicon

If you could separate the Earth out into piles of material, you’d get 32.1 % iron, 30.1% oxygen, 15.1% silicon, and 13.9% magnesium. Of course, most of this iron is actually down at the core of the Earth. If you could actually get down and sample the core, it would be 88% iron.

There are three groups of rocks that make up most of the Earth's crust.

Some rock is made when the hot liquid rock comes from inside the earth (igneous rocks); another type of rock is made when sediment is laid down, usually under the sea (sedimentary rocks); and a third kind of rock is made when the other two are changed by very high temperature or pressure (metamorphic rocks). A very few rocks also fall out of the sky (meteorites).

Below the crust is warm and almost-liquid rock that is always moving around (the Earth's mantle).

Then, there is a thin liquid layer of heated rock (the outer core). This is very hot: 7,000 °C or 13,000 °F.

The middle of the inside of the Earth would be liquid as well but all the weight of the rock above it pushes it back into being solid. This solid middle part (the inner core) is almost all iron. This is what makes the Earth magnetic.

Our planet's rapid spin and molten nickel-iron core give rise to an extensive magnetic field, which, along with the atmosphere, shields us from nearly all of the harmful radiation coming from the Sun and other stars.

Earth's atmosphere protects us from meteors as well, most of which burn up before they can strike the surface.

Earths Magnetic Field

Earth's shape is a spheroid: not quite a sphere because it is slightly squashed on the top and bottom.

As Earth spins around itself, the centrifugal force forces the equator out a little and pulls the poles in a little.

The equator, around the middle of Earth's surface, is about 40,075 kilometres or 24,900 miles long.

Earth's water is believed to have come from comets and asteroids hitting Earth, making the oceans.

Only 3% water of the earth is fresh, rest 97% salted. Of that 3%, over 2% is frozen in ice sheets and glaciers.

Means less than 1% fresh water is found in lakes, rivers and underground.

Within a billion years (that is at about 3.6 billion years ago) the first life evolved, in the Archaean era.

Some bacteria developed photosynthesis, which lets plants make food from the Sun's light and water.

This released a lot of oxygen, which was first taken up by iron in solution. Eventually, free oxygen got into the atmosphere or air, making Earth's surface suitable for aerobic life.

This oxygen also formed the ozone layer which protects Earth's surface from bad ultraviolet radiation from the Sun.

Complex life on the surface of the land did not exist before the ozone layer.

The air animals and plants use to live is only the first level of the air around the Earth (the troposphere).

Above this first level, there are four other levels. The air gets colder as it goes up in the first level; in the second level (the stratosphere), the air gets warmer as it goes up.

This level has a special kind of oxygen called ozone. The ozone in this air keeps living things safe from damaging rays from the Sun.

The middle level (the mesosphere) gets colder and colder with height

The fourth level (the thermosphere) gets warmer and warmer.

The last level (the exosphere) is almost outer space and has very little air at all. It reaches about half the way to the Moon.

The three outer levels have a lot of electric power moving through them; this is called the ionosphere and is important for radio and other electric waves in the air. It is also where the Northern Lights are.

The air also keeps the Earth warm, specially the half turned away from the Sun. Some gasses especially methane and carbon dioxide  work like a blanket to keep things warm.

The Earth’s rotation is gradually slowing.

This deceleration is happening almost imperceptibly, at approximately 17 milliseconds per hundred years, although the rate at which it occurs is not perfectly uniform.

This has the effect of lengthening our days, but it happens so slowly that it could be as much as 140 million years before the length of a day will have increased to 25 hours.

Earth doesn’t take 24 hours to rotate on its axis

It’s actually 23 hours, 56 minutes and 4 seconds. This is the amount of time it takes for the Earth to completely rotate around its axis; astronomers call this a sidereal day.

A year on Earth isn’t 365 days

It’s actually 365.2564 days. It’s this extra .2564 days that creates the need for leap years.

Astronomy - European Space Agency

 

European Space Agency

After World War II, many European scientists left Western Europe to work with the United States.

Although the 1950s boom made it possible for Western European countries to invest in research and specifically in space-related activities, Western European scientists realised solely national projects would not be able to compete with the two main superpowers.

The Western European nations decided to have two agencies: one concerned with developing a launch system, European Launch Development Organization (ELDO), and the other the precursor of the European Space Agency, European Space Research Organisation (ESRO).

The latter was established on 20 March 1964. From 1968 to 1972, ESRO launched seven research satellites.

ESA in its current form was founded with the ESA Convention in 1975, when ESRO was merged with ELDO.

ESA had ten founding member states: Belgium, Denmark, France, Germany, Italy, the Netherlands, Spain, Sweden, Switzerland and the United Kingdom.

The European Space Agency (ESA) is an intergovernmental organisation with now 22-member states dedicated to the exploration of space.

Headquartered in Paris, ESA has a worldwide staff of about 2,000 and an annual budget of about €5.25 billion (2016).

The treaty establishing the European Space Agency reads:

ESA's purpose shall be to provide for, and to promote, for exclusively peaceful purposes, cooperation among European States in space research and technology and their space applications, with a view to their being used for scientific purposes and for operational space applications systems.

ESA launched its first major scientific mission in 1975, Cos-B, a space probe monitoring gamma-ray emission in the universe, which was first worked on by European Space Research Organisation ESRO.

ESA collaborated with NASA on the International Ultraviolet Explorer (IUE), the world's first high-orbit telescope, which was launched in 1978 and operated successfully for 18 years.

Cos-B Space Probe

International Ultraviolet Explorer

A number of successful Earth-orbit projects followed, and in 1986 ESA began Giotto, its first deep-space mission. The spacecraft flew by and studied Halley's Comet and in doing so became the first spacecraft to make closeup observations of a comet.

Hipparcos, a star-mapping mission, was a scientific satellite, launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects in the sky.

 

Giotto

 

Hipparcos

The Solar and Heliospheric Observatory (SOHO) was launched on a Lockheed Martin Atlas II AS launch vehicle on December 2, 1995, to study the Sun, and has discovered over 3000 comets.

Ulysses a robotic space probe whose primary mission was to orbit the Sun and study it at all latitudes. It was launched in 1990 and the Hubble Space Telescope were all jointly carried out with NASA.

SOHO

Later scientific missions in co-operation with NASA include the Cassini–Huygens space probe, to which ESA contributed by building the Titan landing module Huygens.

At the time ESA was formed, its main goals did not encompass human space flight; rather it considered itself to be primarily a scientific research organisation for unmanned space exploration in contrast to its American and Soviet counterparts.

The German Ulf Merbold is considered the first ESA astronaut to fly into space.

He participated in the STS-9 Space Shuttle mission that included the first use of the European-built Spacelab in 1983.

STS-9 marked the beginning of an extensive ESA/NASA joint partnership that included dozens of space flights of ESA astronauts in the following years.

Ulf Merbold

Some of these missions with Spacelab were fully funded and organizationally and scientifically controlled by ESA (such as two missions by Germany and one by Japan) with European astronauts as full crew members rather than guests on board.

Beside paying for Spacelab flights and seats on the shuttles, ESA continued its human space flight co-operation with the Soviet Union and later Russia, including numerous visits to Mir.

During the latter half of the 1980s, European human space flights changed from being the exception to routine and therefore, in 1990, the European Astronaut Centre in Cologne, Germany was established.

It selects and trains prospective astronauts and is responsible for the co-ordination with international partners, especially with regard to the International Space Station.

European Astronaut Centre In Cologne

In the summer of 2008, ESA started to recruit new astronauts so that final selection would be due in spring 2009.

Almost 10,000 people registered as astronaut candidates before registration ended in June 2008. 8,413 fulfilled the initial application criteria.

Of the applicants, 918 were chosen to take part in the first stage of psychological testing, which narrowed down the field to 192.

After two-stage psychological tests and medical evaluation in early 2009, as well as formal interviews, six new members of the European Astronaut Corps were selected - five men and one woman.

ESA has a fleet of different launch vehicles in service with which it competes in all sectors of the launch market. ESA's fleet consists of three major rocket designs: Ariane 5, Soyuz-2 and Vega.

The Ariane 5 rocket is ESA's primary launcher. It has been in service since 1997 and replaced Ariane 4.

Two different variants are currently in use. The heaviest and most used version, the Ariane 5 ECA, delivers two communications satellites of up to 10 tonnes into geostationary transfer orbit GTO.

It failed during its first test flight in 2002, but has since made 71 consecutive successful flights (as of March 2016).

Ariane 5

The other version, Ariane 5 ES, was used to launch the Automated Transfer Vehicle (ATV) to the International Space Station (ISS) and will be used to launch four Galileo navigational satellites at a time.

Soyuz-2 (also called the Soyuz-ST or Soyuz-STK) is a Russian medium payload launcher (ca. 3 metric tons to geostationary transfer orbit GTO) which was brought into ESA service in October 2011.

ESA entered into a €340 million joint venture with the Russian Federal Space Agency over the use of the Soyuz launcher.

ESA benefits because it gains a medium payload launcher, complementing its fleet while saving on development costs.

Soyuz

Vega is ESA's carrier for small satellites. Developed by seven ESA members led by Italy, it is capable of carrying a payload with a mass of between 300 and 1500 kg to an altitude of 700 km, for low polar orbit. Its maiden launch was on 13 February 2012.

The rocket has three solid propulsion stages and a liquid propulsion upper stage for accurate orbital insertion and the ability to place multiple payloads into different orbits.

 

Vega

ESA's space flight programme includes human spaceflight (mainly through participation in the International Space Station programme); the launch and operation of unmanned exploration missions to other planets and the Moon; Earth observation, science and telecommunication; designing launch vehicles; and maintaining a major spaceport, the Guiana Space Centre in French Guiana.

Guiana Space Centre

In robotic science mission and exploration missions, NASA has been ESA's main partner. Cassini–Huygens was a joint NASA-ESA mission, along with the Infrared Space Observatory, and others. Also the Hubble space telescope is a joint project of NASA and ESA.

Future ESA-NASA joint projects include the James Webb Space Telescope and the proposed Laser Interferometer Space Antenna.

ESA entered into a major joint venture with Russia in the form of the Confined Spaces Training and Support Services (CSTS).

The preparation of French Guiana spaceport for launches of Soyuz-2 rockets and other projects including purposed first flight to Mars.

With India, ESA agreed to send instruments into space aboard the Indian Space Research Organisation (ISRO) Chandrayaan-1 in 2008. ESA is also co-operating with Japan, the most notable current project in collaboration with Japan Aerospace Exploration Agency (JAXA) is the BepiColombo mission to Mercury.

Since China has started to invest more money into space activities, the Chinese Space Agency has sought international partnerships.

ESA is, beside the Russian Space Agency, one of its most important partners.

Recently the two space agencies cooperated in the development of the Double Star Mission.

ESA has developed the Automated Transfer Vehicle for ISS resupply. Each ATV has a cargo capacity of 16,903 lb. The first ATV, Jules Verne, was launched on 9 March 2008 and on 3 April 2008 successfully docked with the ISS.

This manoeuvre, considered a major technical feat, involved using automated systems to allow the ATV to track the ISS, moving at 27,000 km/h, and attach itself with an accuracy of 2 cm.

Automated Transfer Vehicle

European Life and Physical Sciences research on board the International Space Station (ISS) is mainly based on the European Programme for Life and Physical Sciences in Space programme that was initiated in 2001.

In May 2007, 29 European countries expressed their support for the European Space Policy in a resolution of the Space Council, unifying the approach of ESA with those of the European Union and their member states.

Prepared jointly by the European Commission and ESA’s Director General Johann Dietrich Woerner, the European Space Policy sets out a basic vision and strategy for the space sector and addresses issues such as security and defence, access to space and exploration.

ESA is not an agency or body of the European Union (EU), and has non-EU countries (Norway, and Switzerland) as members. There are however ties between the two, with various agreements in place and being worked on, to define the legal status of ESA with regard to the EU.

There are common goals between ESA and the EU. ESA has an EU liaison office in Brussels. On certain projects, the EU and ESA co-operate, such as the upcoming Galileo satellite navigation system.

 

Astronomy - Beyond The Visible Spectrum

Beyond The Visible Spectrum

The electromagnetic spectrum is the entire range of frequencies of electromagnetic radiation and their respective wavelengths and photon energies. 

Nearly all types of electromagnetic radiation can be used  to study and characterize matter.

The electromagnetic spectrum extends from below the low frequencies used for modern radio communication to gamma radiation at the short-wavelength (high-frequency) end, thereby covering wavelengths from thousands of kilometres down to a fraction of the size of an atom.

For most of history, visible light was the only known part of the electromagnetic spectrum. The ancient Greeks recognized that light travelled in straight lines and studied some of its properties, including reflection and refraction.

The study of light continued, and during the 16th and 17th centuries conflicting theories regarded light as either a wave or a particle.

The first discovery of electromagnetic radiation other than visible light came in 1800, when William Herschel discovered infrared radiation.

He was studying the temperature of different colours by moving a thermometer through light split by a prism.

He noticed that the highest temperature was beyond red. He theorized that this temperature change was due to "calorific rays" that were a type of light ray that could not be seen.

The next year, Johann Ritter, working at the other end of the spectrum, noticed what he called "chemical rays" (invisible light rays that induced certain chemical reactions).

These behaved similarly to visible violet light rays, but were beyond them in the spectrum. They were later renamed ultraviolet radiation.

Electromagnetic radiation was first linked to electromagnetism in 1845, when Michael Faraday noticed that the polarization of light traveling through a transparent material responded to a magnetic field.

During the 1860s James Maxwell developed four partial differential equations for the electromagnetic field.

Maxwell realized that they must travel at a speed that was about the known speed of light.

This startling coincidence in value led Maxwell to make the inference that light itself is a type of electromagnetic wave.

In 1886 the physicist Heinrich Hertz built an apparatus to generate and detect what are now called radio waves.

Hertz also demonstrated that the new radiation could be both reflected and refracted in the same manner as light.

In 1895 Wilhelm Röntgen noticed a new type of radiation emitted during an experiment with an evacuated tube subjected to a high voltage. He called these radiations x-rays.

The last portion of the electromagnetic spectrum was filled in with the discovery of gamma rays. In 1900 Paul Villard was studying the radioactive emissions of radium when he identified a new type of radiation.

In 1910, British physicist William Henry Bragg demonstrated that gamma rays are electromagnetic radiation.

Astronomers started to investigate portions of the electromagnetic spectrum outside the optical in the 1930s.

Advances in radar and rocket technology during World War II gave this new research a big push, and it has continued to grow ever since.

Non-optical telescopes examine light from the sky at wavelengths other than those of visible light.

Many different types exist to study incoming radio waves, microwaves, infrared and near-infrared rays, ultraviolet rays, X-rays and gamma rays.

The human eye can only see a tiny band of the electromagnetic spectrum.

That tiny band is enough for most day-to-day things you might want to do on Earth, but stars and other celestial objects radiate energy at wavelengths from the shortest (high-energy, high-frequency gamma rays) to the longest (low-energy, low-frequency radio waves).

 

Radio Telescopes

The 76 meter Jodrell Bank

At the far end of the electromagnetic spectrum we find the radio waves, with frequencies less than 1000 megahertz and wavelengths of a metre and more.

Radio waves penetrate the atmosphere easily, unlike higher-frequency radiation, so ground-based observatories can observe them.

Radio telescopes feature three main components that each play an important role in capturing and processing incoming radio signals.

The first is the antenna or ‘dish’ that faces the sky. The Parkes radio telescope in New South Wales, Australia, for instance, has a dish with a diameter of 64 metres, while the Aperture Spherical Telescope in southwest China is 500 metre diameter.

The dish is parabolic, directing radio waves collected over a large area to be focused to a receiver sitting in front of the dish.

The larger the antenna, the weaker the radio source that can be detected, allowing larger telescopes to see more distant and faint objects billions of light years away.

The receiver works with an amplifier to boost the very weak radio signal to make it strong enough for measurement.

Receivers today are so sensitive that they use powerful coolers to minimise thermal noise generated by the movement of atoms in the metal of the structure.

They may be used singly, or linked together electronically in an array. Unlike optical telescopes, radio telescopes can be used in the daytime as well as at night.

Radio telescopes are used to observe a wide array of subjects, including energetic pulsar and quasar systems, galaxies, nebulae, and of course to listen out for potential alien signals.

Microwave Telescope

Microwave radiation spans a range of wavelengths that can be produced by very cold astronomical sources, or by warm sources like protoplanetary disks and clouds of interstellar molecules.

Microwave telescopes must be able to act somewhat like infrared telescopes and somewhat like radio telescopes.

They therefore are built and operated using a fascinating blend of technologies.

Depending on the scientific goals, they can be put in space, in high-altitude balloons, or on the ground at mountaintop observatories.

Some of the most fascinating sources of microwaves lie well outside our solar system, across our galaxy and across the universe.

For example, active galaxies, powered by supermassive black holes at their cores are some of the strongest microwave emitters.

Additionally, these black hole engines can create massive jets of plasma that also glow brightly in the microwave.

Some of these microwave-emitting structures can be larger than the entire galaxy that contains the black hole. 

The center of our own Milky Way galaxy is a microwave source, although it's not so extensive as in other, more active galaxies.

Pulsars (rotating neutron stars) are also strong sources of microwave radiation. These powerful, compact objects are second only to black holes in terms of ultimate density. With powerful magnetic fields and fast rotation rates broad spectrum radiation is produced, with the microwave emission being particularly strong. In fact, most pulsars are usually referred to as "radio pulsars" because of their strong radio emissions, but they can also be "microwave-bright".

When a microwave telescope is pointed around the sky, it detects a faint microwave glow.

The Cosmic Microwave Background Explorer (COBE) satellite made a detailed study of this cosmic microwave background (CMB) beginning in 1989.

Astronomers use the minor fluctuations in the CMB to learn more about the origins and evolution of the universe.

 

The Cosmic Microwave Background

Spitzer Space Infrared Telescope

Sitting just below visible light on the electromagnetic spectrum is infrared light, with wavelengths between 700 nanometres(one billionth of a metre) and 1 millimetre.

Much infrared radiation is absorbed by water vapour in the atmosphere, so infrared telescopes are usually at high altitudes in dry places or even in space, like the Spitzer Space Telescope.

Infrared telescopes are often very similar to optical ones. Mirrors and reflectors are used to direct the infrared light to a detector at the focal point.

The detector registers the incoming radiation, which a computer then converts into a digital image.

Ultraviolet Telescopes

Ultraviolet light is radiation with wavelengths just too short to be visible to human eyes, between 400 nanometres and 0.01 nanometres.

It has less energy than X-rays and gamma rays, and ultraviolet telescopes are more like optical ones.

Mirrors coated in materials that reflect UV radiation, such as silicon carbide, can be used to redirect and focus incoming light.

As redirected light reaches the focal point, a central point where all light beams converge, they are detected using a spectrogram.

This specialised device can separate the UV light into individual wavelength bands in a way akin to splitting visible light into a rainbow.

Analysis of this spectrogram can indicate what the observation target is made of.

This allows astronomers to analyse the composition of interstellar gas clouds, galactic centres and planets in our solar system. This can be particularly useful when looking for elements essential to carbon-based life such as oxygen and carbon.

X-rays are radiation with wavelengths between 10 nanometres(one billionth of a metre). and 0.01 nanometres.

They are used every day to image broken bones and scan suitcases in airports and can also be used to image hot gases floating in space.

Celestial gas clouds and remnants of the explosive deaths of large stars, known as supernovas, are the focus of X-ray telescopes.

X-ray telescopes often use highly reflective mirrors that are coated with dense metals such as gold, nickel or iridium.

Unlike optical mirrors, which can bounce light in any direction, these mirrors can only slightly deflect the path of the X-ray. The mirror is orientated almost parallel to the direction of the incoming X-rays.

The X-rays lightly graze the mirror before moving on, a little like a stone skipping on a pond. By using lots of mirrors, each changing the direction of the radiation by a small amount, enough X-rays can be collected at the detector to produce an image.

To maximise image quality the mirrors are loosely stacked, creating an internal structure resembling the layers of an onion.

In order to get above the Earth's atmosphere, which is opaque to X-rays, X-ray telescopes must be mounted on high altitude rockets, balloons or artificial satellites.

The first X-ray telescope employing grazing-incidence optics was employed in a rocket-borne experiment in 1965 to obtain X-ray images of the Sun.

 

Gamma-ray Telescopes

Gamma radiation is generally defined as radiation of wavelengths less than a hundredth of a nanometre(one billionth of a metre).

Gamma-ray telescopes focus on the highest-energy phenomena in the universe, such as black holes and exploding stars. A high-energy gamma ray may contain a billion times as much energy as a photon of visible light, which can make them difficult to study.

Unlike photons of visible light, that can be redirected using mirrors and reflectors, gamma rays simply pass through most materials.

This means that gamma-ray telescopes must use sophisticated techniques that track the movement of individual gamma rays to construct an image.

One technology that does this, in use in the Fermi Gamma-ray Space Telescope among other places, is called a pair production telescope.

It uses a multi-layer sandwich of converter and detector materials. When a gamma ray enters the front of the detector it hits a converter layer, made of dense material such as lead, which causes the gamma-ray to produce an electron and a positron (known as a particle-antiparticle pair).

The electron and the positron then continue to traverse the telescope, passing through layers of detector material. These layers track the movement of each particle by recording slight bursts of electrical charge along the layer. This trail of bursts allows astronomers to reconstruct the energy and direction of the original gamma ray. Tracing back along that path points to the source of the ray out in space. This data can then be used to create an image.

Astronomy - NASA

The National Aeronautics and Space Administration

 

From 1946, the National Advisory Committee for Aeronautics (NACA) had been experimenting with rocket planes such as the supersonic Bell X-1.

Bell X 1

 

While this new federal agency would conduct all non-military space activity, the Advanced Research Projects Agency (ARPA) was created in February 1958 to develop space technology for military application.

On July 29, 1958, Eisenhower signed the National Aeronautics and Space Act, establishing NASA.

When it began operations on October 1, 1958, NASA absorbed NACA intact; its 8,000 employees, an annual budget of US$100 million, three major research laboratories (Langley Aeronautical Laboratory, Ames Aeronautical Laboratory, and Lewis Flight Propulsion Laboratory) and two small test facilities.

The National Aeronautics and Space Administration is an independent agency of the executive branch of the United States federal government responsible for the civilian space program, as well as aeronautics and aerospace research. Research into the problems of flight within and outside the Earth's atmosphere, and for other purposes.

NASA's birth was directly related to the pressures of national defence.

After World War II, the United States and the Soviet Union were engaged in the Cold War, a broad contest over the ideologies and allegiances of the nonaligned nations.

A significant contributor to NASA's entry into the Space Race with the Soviet Union was the technology from the German rocket program led by Wernhervon Braun, who was now working for the Army Ballistic Missile Agency (ABMA), developing the Redstone Ballistic Missile.

Redstone Ballistic Missile

During this period, space exploration emerged as a major area of contest and became known as the space race.

During the late 1940s, the Department of Defence pursued research and rocketry and upper atmospheric sciences as a means of assuring American leadership in technology.

A major step forward came when President Dwight D. Eisenhower approved a plan to orbit a scientific satellite as part of the International Geophysical Year (IGY) for the period, July 1, 1957 to December 31, 1958, a cooperative effort to gather scientific data about the Earth.

The Soviet Union quickly followed suit, announcing plans to orbit its own satellite.

The Naval Research Laboratory's Project Vanguard was chosen on 9 September 1955 to support the IGY effort, largely because it did not interfere with high-priority ballistic missile development programs.

It used the non-military Viking rocket as its basis while an Army proposal to use the Redstone ballistic missile as the launch vehicle waited in the wings.

Viking Rocket

Project Vanguard enjoyed exceptional publicity throughout the second half of 1955, and all of 1956, but the technological demands upon the program were too great and the funding levels too small to ensure success.

A full-scale crisis resulted on October 4, 1957 when the Soviets launched Sputnik 1, the world's first artificial satellite as its International Geophysical Year entry.

This had a "Pearl Harbour" effect on American public opinion, creating an illusion of a technological gap and provided the impetus for increased spending for aerospace endeavours

The United States launched its first Earth satellite on January 31, 1958, when Explorer 1 documented the existence of radiation zones encircling the Earth.

Shaped by the Earth's magnetic field, what came to be called the Van Allen Radiation Belt, these zones partially dictate the electrical charges in the atmosphere and the solar radiation that reaches Earth.

NASA began to conduct space missions within months of its creation, and during its first twenty years NASA conducted several major programs:

NASA's first high-profile program involving human spaceflight was Project Mercury, an effort to learn if humans could survive the rigors of spaceflight.

On May 5, 1961, Alan B. Shepard Jr. became the first American to fly into space, when he rode his Mercury capsule on a 15-minute suborbital mission.

Alan Shepard

 

Mercury Capsule 

John H. Glenn Jr. became the first U.S. astronaut to orbit the Earth on February 20, 1962.

With six flights, Project Mercury achieved its goal of putting piloted spacecraft into Earth orbit and retrieving the astronauts safely.

John Glenn

Project Gemini built on Mercury's achievements and extended NASA's human spaceflight program to spacecraft built for two astronauts.

Gemini's 10 flights also provided NASA scientists and engineers with more data on weightlessness, perfected re-entry and splashdown procedures, and demonstrated rendezvous and docking in space.

One of the highlights of the program occurred during Gemini 4, on June 3, 1965, when Edward H. White, Jr., became the first U.S. astronaut to conduct a spacewalk.

Gemini Capsule

Edward White

The singular achievement of NASA during its early years involved the human exploration of the Moon, Project Apollo.

Apollo became a NASA priority on May 25th 1961, when President John F. Kennedy announced "I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the Moon and returning him safely to Earth."

In response to the Kennedy decision, NASA was consumed with carrying out Project Apollo and spent the next 11 years doing so.

This effort required significant expenditures, costing $25.4 billion over the life of the program, to make it a reality.

Apollo Capsule

"That's one small step for man, one giant leap for mankind." Neil A. Armstrong uttered these famous words on July 20, 1969, when the Apollo 11 mission fulfilled Kennedy's challenge by successfully landing Armstrong and Edwin E. "Buzz" Aldrin, Jr. on the Moon.

Five more successful lunar landing missions followed.

In total, 12 astronauts walked on the Moon during 6 Apollo lunar landing missions.

After a gap of six years, NASA returned to human spaceflight in 1981, with the advent of the Space Shuttle.

The Shuttle's first mission, STS-1, took off on April 12, 1981, demonstrating that it could take off vertically and glide to an unpowered airplane-like landing.

Space Shuttle Discovery

On STS-6, during April 4-9, 1983, F. Story Musgrave and Donald H. Peterson conducted the first Shuttle Extravehicular Activity EVA, to test new spacesuits and work in the Shuttle's cargo bay.

Sally K. Ride became the first American woman to fly in space when STS-7 lifted off on June 18, 1983, another early milestone of the Shuttle program.

On January 28th 1986 a leak in the joints of one of two Solid Rocket Boosters attached to the Challenger orbiter caused the main liquid fuel tank to explode 73 seconds after launch, killing all 7 crew members.

Tragedy struck again on February 1, 2003, however. As the Columbia orbiter was returning to Earth on the STS-107 mission, it disintegrated about 15 minutes before it was to have landed.

NASA return to flight again in summer 2005 with the STS-114 mission.

There were three Shuttle orbiters left in NASA's fleet: Atlantis, Discovery, and Endeavour.

The core mission of any future space exploration will be humanity's departure from Earth orbit and journeying to the Moon or Mars, this time for extended and perhaps permanent stays.

An initial effort in this area was NASA's Skylab program in 1973. After Apollo, NASA used its huge Saturn rockets to launch a relatively small orbital space workshop.

The Skylab program served as a successful experiment in long-duration human spaceflight.

Skylab

In 1984, Congress authorized NASA to build a major new space station as a base for further exploration of space.

Then Russia, which had many years of experience in long-duration human spaceflight, such as with its Salyut and Mir space stations, joined with the U.S. and other international partners in 1993 to build a joint facility that became known formally as the International Space Station (ISS).

International Space Station

On January 14, 2004, President George W. Bush visited NASA Headquarters and announced a new Vision for Space Exploration.

This Vision entails sending humans back to the Moon and on to Mars by eventually retiring the Shuttle and developing a new, multipurpose Crew Exploration Vehicle.

Robotic scientific exploration and technology development is also folded into this encompassing Vision.

In addition to major human spaceflight programs, there have been significant scientific probes that have explored the Moon, the planets, and other areas of our solar system.

In particular, the 1970s heralded the advent of a new generation of scientific spacecraft. Two similar spacecraft, Pioneer 10 and Pioneer 11, launched on March 2, 1972 and April 5, 1973, respectively, travelled to Jupiter and Saturn to study the composition of interplanetary space.

Voyagers 1 and 2, launched on September 5, 1977 and August 20, 1977, respectively, conducted a "Grand Tour" of our solar system.

In 1990, the Hubble Space Telescope was launched into orbit around the Earth. Unfortunately, NASA scientists soon discovered that a microscopic spherical aberration in the polishing of the Hubble's mirror significantly limited the instrument's observing power.

Voyager

 

Hubble Space Telescope

During a previously scheduled servicing mission in December 1993, a team of astronauts performed a dramatic series of spacewalks to install a corrective optics package and other hardware.

NASA suffered another major disappointment when the Mars Observer spacecraft disappeared on August 21, 1993, just three days before it was to go into orbit around the red planet.

In response, NASA began developing a series of "better, faster, cheaper" spacecraft to go to Mars.

Mars Global Surveyor was the first of these spacecraft; it was launched on November 7, 1996, and has been in a Martian orbit mapping Mars since 1998.

Mars Pathfinder spacecraft landed on Mars on July 4, 1997 and explored the surface of the planet with its miniature rover, Sojourner.

Over the years, NASA has continued to look for life beyond our planet.

In 1975, NASA launched the two Viking spacecraft to look for basic signs of life on Mars.

In 1996 a probe from the Galileo spacecraft that was examining Jupiter and its moon, Europa, revealed that Europa may contain ice or even liquid water,

NASA also has used radio astronomy to scan the heavens for potential signals from extra-terrestrial intelligent life.

1990s, organized an "Origins" program to search for life using powerful new telescopes and biological techniques. More recently scientists have found more and more evidence that water used to be present on Mars.

Building on its roots in the National Advisory Committee for Aeronautics, NASA has continued to conduct many types of cutting-edge aeronautics research on aerodynamics, wind shear, and other important topics using wind tunnels, flight testing, and computer simulations.

NASA did pioneering work in space applications such as communications satellites in the 1960s. The Echo, Telstar, Relay, and Syncom satellites were built by NASA or by the private sector based on significant NASA advances.

Since its inception in 1958, NASA has accomplished many great scientific and technological feats. NASA technology has been adapted for many non-aerospace uses by the private sector.

NASA remains a leading force in scientific research and in stimulating public interest in aerospace exploration, as well as science and technology in general.