(such as stars, planets, comets, and galaxies) and phenomena that originate outside the Earth’s atmosphere (such as the cosmic background radiation). It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the formation and development of the universe.
Wikipedia: link
Other References:
http://www.astronomy2009.org
http://www.hubblesite.org
http://www.astrofind.net/
http://www.universetoday.com/
http://www.astrolink.ir/en
http://www.astronomy.com/
http://www.skyandtelescope.com/
http://www.astronomy.net.nz
http://antwrp.gsfc.nasa.gov/apod/
http://www.aip.org/history/cosmology/index.htm
http://www.vega.org.uk/video/subseries/16
