Astronomy is the study of science of all the celestial bodies in the universe: planets, stars, galaxies etc., their origin, behavior, compositions and physical effects.
...And He brought him forth abroad, and said: Look now toward heaven,
and tell the stars, if thou be able to number them:
and He said unto him: So shall thy seed be. (Gen. 15:5)
The mystery of the Universe has overwhelmed humankind since the dawn of the civilization. The passage from the Book of Genesis told the story of God's promise to patriarch Abraham by asking a rather difficult question: count the number of stars. Unaided, our naked eyes may perhaps see around a thousand stars in a clear dark sky. With a small telescope, the number quickly creeps up to hundreds of thousands. Even until today we still do not know the exact size and age of the universe, let alone the number of stars
(and countless other celestial bodies) contained in it. We could only arbitrarily say there are billions of billions of stars.
The origin of astronomy (often intermingle with astrology) was conceived since prehistoric times, perhaps around 5000 BC with the Chaldeans and Mesopotamia. It was discovered by the ancients that the celestial bodies exhibited some regularities of behavior and form certain identifiable patterns. These bodies can be grouped together to form constellations. Indeed, detailed constellation maps were already compiled by several civilizations such as the Babylonians, Egyptians, Maya and the Chinese.
However, astronomy was greatly advanced by Copernicus (1473-1543), a Polish Mathematician. Although his theory was not entirely correct, he wrote that the Earth is orbiting round the Sun, instead of the other way round. His idea was supported by few others, notably J. Kepler (1571-1630), a German mathematician, who discovered the laws of planetary motions.
However, astronomy took another great leap when Galileo Galilei (1564-1642), who also believed the theory of Copernicus, pointed his telescope, a new invention from Holland, at the sky. Among many other celestial features, he discovered craters and mountains on the moon, four satellites orbit the planet Jupiter and rings of planet Saturn. The use of telescopes open up a new chapter on astronomy and have become indispensible tools for astronomers to study celestial objects in great details.