Astronomy Picture of the Day

What is Astronomy?

Astronomy is the science dealing with all the celestial bodies in the universe, including the planets and their satellites, comets and meteors, the stars and interstellar matter, the star systems known as galaxies, clusters of galaxies, and quasars.

Astronomy is such a broad topic that astronomers specialize in one or more parts of the field. For example, the study of the solar system is a different area of specialization than the study of stars. Astronomers who study our galaxy, the Milky Way, often use techniques different from those used by astronomers who study distant galaxies. Many planetary astronomers, such as scientists who study Mars, may have geology backgrounds and not consider themselves astronomers at all. Solar astronomers use different telescopes than night time astronomers use, because the Sun is so bright. Theoretical astronomers may never use telescopes at all. Instead, these astronomers use existing data or sometimes only previous theoretical results to develop and test theories. An increasing field of astronomy is computational astronomy, in which astronomers use computers to simulate astronomical events. Examples of events for which simulations are useful include the formation of the earliest galaxies of the universe or the explosion of a star to make a supernova.

Astronomers learn about astronomical objects by observing the energy they emit. These objects emit energy in the form of electromagnetic radiation. This radiation travels throughout the universe in the form of waves and can range from gamma rays, which have extremely short wavelengths, to visible light, to radio waves, which are very long. The entire range of these different wavelengths makes up the electromagnetic spectrum.

Modern astronomy is divided into several branches:

Astrophysics, the branch of astronomy that seeks to understand the birth, evolution, and end states of celestial objects and systems in terms of the physical laws that govern them. For each object or system under study, astrophysicists observe radiations emitted over the entire electromagnetic spectrum and variations of these emissions over time . This information is then interpreted with the aid of theoretical models. It is the task of such a model to explain the mechanisms by which radiation is generated within or near the object, and how the radiation then escapes. Radiation measurements can be used to estimate the distribution and energy states of the atoms, as well as the kinds of atoms, making up the object. The temperatures and pressures in the object may then be estimated using the laws of thermodynamics.
Models of celestial objects in equilibrium are based on balances among the forces being exerted on and within the objects, with slow evolution taking place as nuclear and chemical transformations occur. Cataclysmic phenomena are interpreted in terms of models in which these forces are out of balance.

STARS

Space Telescope Science Institute/Hubble Space Telescope Public Release Images

Hubble Space Telescope: New Views of the Universe [RealPlayer, QuickTime]
http://hubble.stsci.edu/discoveries/hstexhibit/
This site is a companion to the travelling Space Telescope Science
Institute (STScI) and Smithsonian exhibition. Offerings include
numerous brief, illustrated fact sheets on the telescope and the
universe, movies, related links, and information on the travelling
exhibit. This modest but well-crafted site offers a nice educational
diversion for anyone interested in astronomy.

NASA's Space Science Photo Gallery From the National Space Science Data Center, a collection of images covering everything from the Earth's surface to the deepest astronomical objects.
Skyview: The Goddard Space Flight Center's virtual observatory. See any part of the sky in any wavelength.

Pulstar