Astronomy is a field of science that studies the nature and motions of celestial bodies. This includes studying objects such as stars, planets and entire galaxies.
Those in early civilizations recognized and kept records of the regularity of celestial motions, making astronomy the oldest of the physical sciences. Early astronomers used their observations to help create the first calendars, dividing the months and years based on their observations.
Nicolaus Copernicus helped to create modern astronomy in 1543 with the publication of "On the Revolutions of the Celestial Spheres." This work claimed that the sun, and not the Earth, was the center of solar system and that the Earth rotated on its axis. Another astronomer, Galileo Galilei, used a telescope for astronomical purposes for the first time in history and made observations of four of Jupiter's moons and the phases of Venus. This evidence provided support of Copernicus' ideas. Later, Isaac Newton helped to unite the sciences of astronomy and physics with his laws of motion and theory of universal gravitation.
Techniques that made use of photography and spectroscopy revolutionized astronomy in the 19th century. This helped astronomers shift from studying the positions of stars to studying their composition. In addition, other technological advances, such as larger telescopes, have helped astronomers learn more about the universe.