Astronomy Glossary

The point at which a body orbiting the Earth's Sun is furthest from the Sun.

The point at which a body orbiting the Earth (such as the Moon or an artificial satellite) is furthest from the Earth.

Any pattern of stars recognizable in Earth's night sky. An asterism may form part of an official constellation or it may be composed of stars from more than one constellation.

A region of space lying between Mars (1.5 AU) and Jupiter (5.2 AU), where the great majority of the asteroids are found. None of the belt asteroids have retrograde motion.

Also called a celestial object.
A type of naturally occurring physical entity, association, or structure that exists within the observable universe but is a more complex, less cohesively bound structure than an astronomical body, consisting perhaps of multiple bodies or even other objects with substructures, such as a planetary system, star cluster, nebula, or galaxy. Though the terms astronomical "object" and astronomical "body" are often used interchangeably, there are technical distinctions.

The scientific study of celestial objects and phenomena, the origins of those objects and phenomena, and their evolution.

The branch of astronomy that employs principles of physics and chemistry to determine the nature of astronomical objects and phenomena, examining properties such as luminosity, density, temperature, and chemical composition (rather than the positions or motions of objects in space, which is more specifically the emphasis of celestial mechanics).