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ID:
134916
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| Summary/Abstract |
Astronomy starts at the point to which chemistry has brought us: atoms. The basic stuff of which the planets and stars are made is the same as the terrestrial material discussed and analyzed in the first set of essays in this volume. These are the chemical elements, from hydrogen to uranium. Hydrogen, found with oxygen in our plentiful oceanic water, is by far the most abundant element in the universe; iron is the most common of the heavier elements. All the combinations of atoms in the complex chemical com- pounds studied by chemists on Earth are also possible components of the objects that we see in the cosmos. Although almost all of the regions that we astronomers study are so hot that the more complicated compounds would be torn apart by the heat, some surprisingly unstable organic molecules. such as cyanopolyynes. have been detected in cold regions of space with very low density of matter. Nevertheless. the astronomical world is simpler than the chemical world of the laboratory or the real biological world.
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| 2 |
ID:
134919
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| Summary/Abstract |
Astronomers can map the sky in many ways: observing in different regions of the electromagnetic spectrum, obtaining spectra of stars and galaxies to determine their physical properties and distances, and repeatedly observing to measure the variability, explosions, and motions of celestial objects. In this review I describe recent surveys of the sky astronomers have carried out, focusing on those in the visible part of the spectrum. I describe in detail the Sloan Digital Sky Survey, an ongoing imaging and spectroscopic survey of over one quarter of the celestial sphere. I also discuss some of the major surveys planned for the next decade, using telescopes both on the ground and in space.
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| 3 |
ID:
134920
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| Summary/Abstract |
Quasars emit more energy than any other object in the universe, yet are not much bigger than our solar system. Quasars are powered by giant black holes of up to ten billion (1010) times the mass of the sun. Their enormous luminosities are the result of frictional forces acting upon matter as it spirals toward the black hole, heating the gas until it glows. We also believe that black holes of one million to ten billion solar masses – dead quasars – are present at the centers of most galaxies, including our own. The mass of the central black hole appears to be closely related to other properties of its host galaxy, such as the total mass in stars, but the origin of this relation and the role that black holes play in the formation of galaxies are still mysteries.
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