Astronomy is the scientific study of celestial objects (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.

Astronomy is one of the oldest sciences. Astronomers of early civilizations performed methodical observations of the night sky, and astronomical artifacts have been found from much earlier periods. However, the invention of the telescope was required before astronomy was able to develop into a modern science. Historically, astronomy has included disciplines as diverse as astrometry, celestial navigation, observational astronomy, the making of calendars, and even astrology, but professional astronomy is nowadays often considered to be synonymous with astrophysics.

Since the 20th century, the field of professional astronomy split into observational and theoretical branches. Observational astronomy is focused on acquiring and analyzing data, mainly using basic principles of physics. Theoretical astronomy is oriented towards the development of computer or analytical models to describe astronomical objects and phenomena. The two fields complement each other, with theoretical astronomy seeking to explain the observational results, and observations being used to confirm theoretical results.

Amateur astronomers have contributed to many important astronomical discoveries, and astronomy is one of the few sciences where amateurs can still play an active role, especially in the discovery and observation of transient phenomena. Old or even ancient astronomy is not to be confused with astrology, the belief system which claims that human affairs are correlated with the positions of celestial objects. Although the two fields share a common origin and a part of their methods (namely, the use of ephemerides), they are distinct.

2009 has been declared by the UN to be the International Year of Astronomy 2009. The focus is on enhancing the public’s understanding and engagement with astronomy.

Astronomy Wikipedia

History of Astronomy  Wikipedia

In the News ...

How can we search for life on icy moons such as Europa?   PhysOrg - November 25, 2014

Our solar system is host to a wealth of icy worlds that may have water beneath the surface. The Cassini spacecraft recently uncovered evidence of a possible ocean under the surface of Saturn's moon, Mimas. Mimas is not alone in the possibility of having a global ocean, which would potentially provide a foothold for life to exist. Other worlds under examination include Jupiter's moon, Europa. In 2013, NASA's Hubble Space Telescope observed evidence that Europa erupts water, while the Cassini spacecraft has observed geysers spewing on Saturn's moon, Enceladus.

Earth Calling E.T.: New Project Begins Beaming Your Messages Into Deep Space   Live Science - June 19, 2013

In 18 years, messages beamed out into space from Earth by a new alien-messaging project Monday (June 17) will reach a distant star system known as Gliese 526. Officials with the Lone Signal project - a newly launched website designed to send user-written notices to any extraterrestrials who may receive them - hope that their messages might open the first dialogue between Earth and other intelligent life forms. One of the company's first message beamed to the Gliese 526 system, located 17.6 light-years from Earth was sent by famous futurist Ray Kurzweil and reads: "Greetings to Gliese 526 from Singularity University. As you receive this, our computers have made us smarter, the better to understand you and the wisdom of the universe..."