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Observational astronomy

Astronomy is a natural science that is the study of celestial objects such as asteroids, comets, moons, planets, stars, black holes, nebulae, galaxies. It also includes the physics, chemistry, and evolution of such objects. Astronomy also investigates phenomena that originate outside the atmosphere of Earth, including supernovae explosions, gamma-ray bursts, and cosmic microwave background radiation.

A related but distinct subject, cosmology, is concerned with studying the universe as a whole.

A collection of planet sized objects including  the star sirius. These are all objects of the study of astronomy, including the place of Earth in space. Image: wikipedia

History of astronomy

Astronomy is one of the oldest sciences. Prehistoric cultures have left astronomical artifacts such as the Egyptian monuments and Nubian monuments, and early civilisations such as the Babylonians, Greeks, Chinese, Indians, Iranians and Maya performed methodical observations of the night sky.

The telescope

The invention of different types of telescopes 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, and the making of calendars, but professional astronomy is nowadays often considered to be synonymous with astrophysics.

A replica of Isaac Newton's second reflecting telescope of 1672, Cambridge. image: wikipedia

During the 20th century, the field of professional astronomy split into observational and theoretical branches. 

Observational astronomy

 is focused on acquiring data from observations of astronomical objects, which is then analyzed using basic principles of physics.  This includes basic observations of the movement of the sun (for example observations of the solstice and equinox), moon, stars and planets.

Theoretical astronomy

 is oriented toward 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.

A computer simulation showing the result of a simulation of the collision of two disk galaxies, run using the NEMO package. image: wikipedia

Amateur astronomy

Astronomy is one of the few sciences where amateurs can still play an active role, especially in the discovery and observation of transient phenomena. Amateur astronomers have contributed to many important astronomical discoveries.

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 they are now entirely distinct.

The word "astronomy" comes from the Greek "aster" meaning star and the suffix "_nomy" meaning "laws of" the Greek word nomos means law or rule.

Which is all pretty cool!