Now, What you are about to see, is very long.
Personally i dont mind if this stuff looks like a waste of time to read to you, but if you have at least any interest in astronomy and stuff, why not just sit and glaze over all the very boring red-colured text that makes you think I didn't write it all, when in fact... I didn't!
(And yes if you wanted to know, there are REALLY cool pics too!).
Crab Nebula An exploding supernova leaves behind a rapidly expanding cloud of gaseous material called a nebula. The Crab Nebula was produced when a star in our galaxy exploded; the light from the explosion was observed by Chinese astronomers in 1054. At the centre of the Nebula lies a pulsar, a dense, rapidly spinning star.Hale Observatories/Science Source/Photo Researchers, Inc.
In the late 18th century Sir William Herschel constructed the largest reflecting telescopes of his day and used them to explore the heavens. He discovered not only the planet Uranus but also several satellites and many double stars, in addition to myriad star clusters and nebulae. His counts of stars in different regions of the heavens convinced Herschel that the Sun is one of a vast cloud of stars, a cloud shaped like a grindstone. According to his analogy, a person living on a small planet near the Sun deep inside the “grindstone” looks towards its rim and is able to see a belt of faint, distant stars, which is called the Milky Way, stretching completely around the sky; looking above or below, the person is able to see relatively few nearby stars.
Return of Halley's Comet Halley’s Comet reappears approximately every 76 years; this photograph (below), taken in New Zealand in 1986, shows the comet during its most recent approach to the Sun. Comets become visible near the Sun because solar radiation vaporizes parts of the icy nucleus, forming the comet’s coma and tail.Barney Magrath/Science Source/Photo Researchers, Inc.
Modern investigations confirm this picture, except that the solar system is now known to be about two thirds of the way out from the centre. The name “Milky Way” or “galaxy” is often applied to the whole system. The stars in the system are all gravitationally bound and orbiting about a distant centre. A knowledge of star distances is of primary importance in studying the structure of the Milky Way. The parallax method of determining these distances can be applied only to the nearest stars. A particular class of stars exists, the Cepheid variables, which vary in brightness with periods that depend on their intrinsic intensities. Comparison of the observed brightness of such a star with the intrinsic brightness calculated from its period provides a means of determining its distance. Following the discovery of the relation between period and luminosity by Henrietta Swan Leavitt, Harlow Shapley used the Cepheid variables scattered throughout the Milky Way to measure its size. A ray of light, moving at a speed of about 300,000 km/s (186,300 mi/s), would require 400,000 years to traverse the Milky Way from edge to edge of its extended halo (described below). The visible spiral is approximately 100,000 light years across. Altogether, the Milky Way consists of about 100 billion stars orbiting about a common centre. The Sun, located about 30,000 light years from the centre of the Milky Way, travels at a speed of about 210 km/s (130 mi/s) and completes an entire revolution approximately every 250 million years.
Image of Asteroid 243 Ida Asteroids are extremely small planets that orbit the sun and are situated primarily between the orbits of Mars and Jupiter. The Galileo spacecraft, a space probe launched by the United States National Aeronautics and Space Administration (NASA), photographed asteroid 243 Ida, above, in August 1993. The space probe detected a moon orbiting Ida, making it the only asteroid known to have a satellite.Jet Propulsion Laboratory/Liaison Agency
The Milky Way includes great quantities of dust and gas scattered between the stars. This interstellar matter intercepts the visible light emitted by distant stars so that observers on Earth cannot view in detail distant parts of the Milky Way. A new branch of astronomy was initiated when the American electronics engineer Karl G. Jansky discovered in 1931-1932 that radio waves are emitted from the Milky Way. Later study traced this radiation partly to interstellar matter and partly to discrete sources, originally called radio stars. Radio waves emitted by distant parts of the Milky Way can penetrate interstellar matter that is opaque to visible light, and thus enable astronomers to observe regions hidden to optical instruments. Such observations have revealed the Milky Way to be a barred spiral galaxy with a flattened central bulge of old stars, an outer disc of both older stars and hot young stars that make up the spiral arms, and a large, extended halo of faint stars.
The nucleus of the Milky Way was until recently a mysterious region, obscured from view by dark clouds of interstellar dust. Astronomers began getting their first detailed picture of the region in 1983, when the Infrared Astronomy Satellite (IRAS) was launched. Freed from the obscuring effects of the Earth’s atmosphere, sensors aboard IRAS recorded in unprecedented detail the positions and shapes of the myriad sources of infrared energy that occupy the heart of the Milky Way. Among these was discovered one massive object, not a star and too compact to be a star cluster, that may yet prove to be a black hole.
Advances in observation techniques led to the opening of a new branch of astronomy in the mid-1990s. In 1995 a Swiss team of astronomers announced the discovery of the first extrasolar planet orbiting a Sun-like star. They had deduced the planet's mass, orbital period, and distance from the star by measuring small wobbles in the star's axis of rotation caused by the pull of the planet's mass. Over 30 such planets have now been discovered, including, in 1999, the first multiple-planet system. While the technique was initially only sensitive enough to detect planets that were the size of Jupiter and orbiting closer to their star than the Earth is to the Sun, refinements are expected eventually to enable it to detect planets the size of Earth. Indeed, two smaller planets, about the size of Saturn, were discovered early in 2000. A different approach aims to image extrasolar planets directly, by designing space-based telescopes equipped with a central baffle to block the glare of the parent star's light. By the end of the 1990s a number of such designs had been proposed. The first visual proof of the existence of an extrasolar planet was announced at the end of 1999, when a tiny dip in the light of a star was observed just at the time when a planet was due to pass in front of it. Such observations allow much more information to be obtained about the planetary body, in particular its diameter.
Our solar system lies in one of the spiral arms of the disc-shaped galaxy called the Milky Way (left). This photograph looks towards the centre of the Milky Way, 30,000 light years away. Bright star clusters are visible in the image along with darker areas of dust and gas.Morton-Milon/Science Source/Photo Researchers, Inc.
The Milky Way is only one of many galaxies that populate the known universe. By 1924 studies conducted by the American astronomer Edwin Hubble had shown that the spiral nebulae are individual galaxies like the Milky Way, located at very great distances. Although some galaxies have a spiral form, like the Milky Way, other galaxies are ellipsoidal, without spiral arms; others still are of irregular shape, sometimes showing traces of spiral arms.
Quasar This false-colour radio map of a quasar was made by the Very Large Array, a huge multi-antenna radio telescope in New Mexico. The quasar’s extremely bright core (bright red spot at top) is emitting a clumpy jet of high-energy matter (line of red patches). Quasars are thought to be the high-energy nuclei of extremely distant, young galaxies, and may derive their extraordinary quantities of energy from giant black holes at their cores. Because a quasar’s light takes billions of years to reach the Earth, astronomers can study them to learn about earlier stages in the history of the universe.NRAO/Photo Researchers, Inc.
Spectral analysis of the light from the galaxies shows that the stars making up these systems are composed of the chemical elements known on Earth, dominated, like the Sun, by hydrogen. Such analysis also demonstrates a red shift, indicating that the galaxies (or rather, clusters of galaxies) are all moving away from each other: the more distant a galaxy, the faster its recession. Althoughthis red shift is analogous to the Doppler effect, it is explained by the general theory of relativity as evidence that the universe is expanding, with space itself stretching, not that the galaxies are flying apart through space. This means that the universe originated from an extremely hot, dense state in an outburst called the big bang. Space and time, as well as energy and matter, were created in the big bang, which was not an explosion at a point in space.
Radio Map The Parkes 64-m (210-ft) radio telescope in Australia produced this radio map of the Large Magellanic Cloud. The colours of the image correspond to radio wave intensity; black is the least intense, red the most. A radio map often reveals structures that are invisible to visible-light telescopes.Max-Planck-Institut for Radioastronomie/Science Source/Photo Researchers, Inc.
Radiation filling the universe has been cooling ever since the 'big bang'; its present temperature is about 3 K (3° C above absolute zero, or about -454° F). Radiation of this temperature, coming from all directions in the sky, was discovered in 1965 by the American physicists Arno Penzias and Robert Wilson, and is the best indicator of the early history of the universe. Einstein’s theory of gravitation, the general theory of relativity, predicted that the universe would be found to be expanding, although Einstein himself resisted this conclusion; the big bang description of the universe is essentially based on general relativity. A combination of theory and observation indicates that the big bang occurred at least 13 billion years ago.
Galaxy M100 (below) The spiral galaxy M100 is between 35 million and 80 million light-years from the earth. The Hubble Space Telescope captured this image of the core and spiral arms of M100 after repairs had been made to the telescope in December 1993.NASA/Liaison Agency
Quasars, discovered in the 1960s, are the energetic nuclei of very distant galaxies. They are so bright that a quasar masks the light from the surrounding galaxy, just as the light from a pocket torch could not be seen in the glare from a searchlight. Often quasars occur in extremely distant clusters of galaxies. The spectral lines of quasars display very large red shifts, which indicates that some of these objects are receding from us at speeds of 80 per cent of the speed of light or more. Because the red shift is proportional to distance, this means that they are among the most distant of cosmological objects, and that we see them by light that left them when the universe was only about 7 per cent of its present age, some 1 billion years after the big bang. In 1998 astronomers announced that observations of supernovae in distant galaxies had a higher red shift than predicted, suggesting that the expansion of the universe is actually accelerating.
These sources provide additional information on Astronomy.
However, everything described above may be no more than the tip of the universal iceberg. From the way that galaxies move within clusters, astronomers calculate that they are being held in the gravitational grip of at least 10 times, and perhaps 100 times, as much matter as we can see in the form of bright stars and galaxies. Observations in 1998 hinted at an inverse relationship between dark and normal matter, with the smallest, faintest galaxies having motions that indicated the presence of the greatest amount of dark matter. The nature of this dark matter is still a mystery, and determining its composition will be one of the most important problems facing astronomers at the beginning of the 21st century.
The nearest star, Alpha Centauri, is about 260,000 times farther from the Earth than is the Sun. It is 4.3 light years away; a light year is the distance light would travel in one year, at a speed of 300,000 km/s. The entire Milky Way Galaxy is about 100,000 light years across, but only some 1,000 light years thick.
All stars are hot, gaseous bodies like the Sun, but differ from it and from one another in minor ways. The most important physical data about a star are its intrinsic brightness, size, mass, and chemical composition. Although all stars seem much fainter than the Sun because of their great distances from the Earth, some of them are intrinsically brighter than the Sun (see Magnitude). Star masses can be determined directly for the Sun and for pairs of stars, in binary systems, that are seen to orbit around each other. Astronomers apply the law of gravitation and Kepler’s laws to determine the stellar masses mathematically. Of the 50 nearest stars for which information is fairly complete, 10 per cent are brighter, larger, and more massive than the Sun. Spectroscopic studies show that the stars are composed largely of hydrogen.
The source of the vast quantities of energy radiated by the Sun was long a mystery. The Sun emits energy at the rate of 3.8 × 1026 watts. Geological evidence shows that life has existed on Earth for billions of years, indicating that solar energy must have been expended at about its present rate for that long. Even before the processes by which the Sun generates energy were understood, however, the pioneering astrophysicist Arthur Eddington was able, in the 1920s, to work out the internal structure of stars from the laws of physics. No matter how the Sun generates its energy, for example, it is straightforward to calculate how hot it must be inside from its known mass and the rate at which it is radiating. This enabled Eddington to work out the temperature at the heart of the Sun, about 15 million degrees C (27 million degrees F).
In the 1930s it was clear that the energy generation process must involve the conversion of hydrogen into helium inside the Sun, and in 1938 the American physicist Hans Bethe showed how this could be achieved in a series of nuclear interactions called the proton-proton chain. This process involves the conversion of some of the mass of the original hydrogen nuclei into energy. Overall, over 4 million tonnes of mass are converted into pure energy at the heart of the Sun each second, in line with the equation, devised by Albert Einstein, E = mc2. This says that mass and energy are interchangeable, and that the energy E locked up in a mass m is equal to the mass multiplied by the square of c, the speed of light.
Observation and theory combine to reveal the principal steps in the life cycle of a star. The protostar begins to condense from inside a relatively dense and cool cloud of interstellar gas. This contraction converts gravitational energy into heat, and this internal heating increases the temperature at the heart of the star to the point where nuclear reactions can begin (a temperature of about 15 million degrees C/27 million degrees F). The heat generated by these reactions then halts the contraction, and the star settles down to a period as a hydrogen-burning main-sequence star. In the case of a star with about the same mass as the Sun, the main-sequence phase lasts about 10 billion years. Near the end of its lifetime, such a star expands to a red giant state, expels gas from its atmosphere, contracts again, and then shrinks and cools as a dense white dwarf star, containing about as much mass as the Sun in a volume roughly the same as the Earth. Stars with more mass run through their life cycles more quickly; those that end their time on the main sequence with more than about ten times as much mass as the Sun explode as supernovae. see Star: Evolution of Stars.
In 1967 a British radio astronomer, Jocelyn Bell, discovered rapidly varying radio signals coming from well-defined points on the sky. The objects producing this noise were named pulsars, a contraction of pulsating radio sources, but were soon shown to be rotating compact objects, spinning several times a second and sweeping beams of radio noise around the sky like a radio lighthouse. In order to spin so rapidly without breaking apart, pulsars must consist of matter even more condensed than white dwarfs, with about as much mass as our Sun packed into a sphere less than 10 km (6 mi) across, about as big as a large mountain on Earth. A pulsar is a fast-spinning neutron star, a tightly packed mass of neutrons, like a single huge atomic nucleus. It is the densest object in the universe apart from a black hole. Pulsars are formed as the remnants of supernova explosions.
Even a mass of neutrons cannot hold itself up against the inward tug of gravity if the mass left over from the supernova explosion is more than about three times the mass of Sun. Any neutron star that tries to form with more mass than this will collapse to form a black hole, which has such a strong gravitational field that nothing, not even radiation, can escape from it. In 1974 the existence of a black hole in the constellation Cygnus was suggested by detection of X-radiation from hot gas swirling in a ring as it fell into the black hole. The X-ray source was a member of a binary system, so its mass could be estimated, and turned out to be above the limit of stability for a neutron star. Since then several black hole candidates have been identified. There is also strong evidence that much larger black holes, containing hundreds of millions of times as much mass as our Sun, lie at the hearts of many galaxies, and may provide the power source for quasars.
All text was copied from The Encarta Encyclopedia 2002 EditionTM For Windows
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