An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists within the observable universe. In astronomy, the terms object and body are often used interchangeably. However, an astronomical body or celestial body is a single, tightly bound, contiguous entity, while an astronomical or celestial object is a complex, less cohesively bound structure, which may consist of multiple bodies or even other objects with substructures.
Examples of astronomical objects include planetary systems, star clusters, nebulae, and galaxies, while asteroids, moons, planets, and stars are astronomical bodies. A comet may be identified as both body and object: It is a body when referring to the frozen nucleus of ice and dust, and an object when describing the entire comet with its diffuse coma and tail.
Scientific Revolution and Copernican Revolution
Astronomical objects such as stars, planets, nebulae, asteroids and comets have been observed for thousands of years, although early cultures thought of these bodies as gods or deities. These early cultures found the movements of the bodies very important as they used these objects to help navigate over long distances, tell between the seasons, and to determine when to plant crops. During the Middle-Ages, cultures began to study the movements of these bodies more closely. Several astronomers of the Middle-East began to make detailed descriptions of stars and nebulae, and would make more accurate calendars based on the movements of these stars and planets. In Europe, astronomers focused more on devices to help study the celestial objects and creating textbooks, guides, and universities to teach people more about astronomy.
During the scientific revolution, in 1543, Nicolaus Copernicus's heliocentric model was published. This model described the Earth, along with all of the other planets as being astronomical bodies which orbited around the Sun located in the center of the Solar System.
