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The word astronomy is derived from Greek words meaning 'law of the stars'.
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Astronomy is not the same as astrology, which is a belief system about human behaviour in regards to the position of space objects.
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Throughout history astronomy has been used to determine seasons, which helped with crop planting and harvesting, and to help to determine the length of a year.
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Ancient astrology was used to help determine the timing of specific cultural ceremonies.
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Aristarchus of Samos (3rd century B.C.) was the first to estimate the distance and size of the moon and the sun. He also was the first to create an astrolabe, an ancient tool used to solve problems relating to time and the sun and star's positions.
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Astronomy has helped to determine many facts about the universe.
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Nicolaus Copernicus was a 16th century mathematician who presented the first heliocentric model of the universe (suggesting that the sun was the center of the universe and that planets revolved around the sun).
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Galileo Galilei and Johannes Kepler both expanded upon Nicolaus Copernicus' ideas.
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Sir Isaac Newton was the first to explain the motion of the planets. He determined the law of gravity and invented the idea of celestial dynamics (motion of celestial objects).
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Sir Isaac Newton invented the reflecting telescope in 1668, but it was another 100 years before it became a popular tool in astronomy.
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Observational astronomy involves recording data through observation with astronomical tools such as telescopes.
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Observational astronomy is further divided into radio astronomy (study of radiation with wavelengths of 1 millimeter or more), infrared astronomy (detection and analysis of infrared radiation), optical astronomy (images drawn by hand), ultraviolet astronomy (observation of ultraviolet wavelengths from the upper atmosphere or from space), X-ray astronomy (use of X-ray wavelength to study objects in space), and gamma-ray astronomy (study of space objects at shortest wavelengths).
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Theoretical astronomy is conducted with the use of analytical models to study topics such as stellar dynamics, galaxy formation, cosmic ray origins, matter in the universe, evolution, general relativity, and astroparticle physics.
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Theories of theoretical astronomy include the Big Bang Theory, Cosmic inflation, the Lambda-CDM model, and dark matter.
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Astrology has given way to many subfields of the science including solar astronomy, planetary science, stellar astronomy, galactic astronomy, extragalactic astronomy, and cosmology.
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Astronomy has created many unanswered questions, including the questions of: whether there is life on other planets, the nature of dark energy and dark matter, and what is the eventual fate of the universe?
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