Astronomy Definition – What is Astronomy?

Astronomy is the scientific study of celestial objects and phenomena, including the structure, motion, and evolution of stars, planets, and other astronomical bodies. The field of astronomy has two broad branches — observational astronomy, which focuses on using telescopes and cameras to gather data about the night sky, and theoretical astronomy, which uses this data to understand how these objects and phenomena work.

Astrometry is the ancient branch of astronomy that deals with precise measurements of the positions and movements of celestial bodies, such as the Sun, Moon, and planets. This includes the prediction of solar and lunar eclipses and meteor showers. It also encompasses exoplanetology, the relatively new field that aims to discover and characterize planets outside our Solar System.

The phenomenon that occurs when two astronomical objects or spacecraft have the same right ascension and/or ecliptic longitude, such that they appear to closely approach each other in the sky from a third body’s perspective. The objects can be either terrestrial (earth-bound), extraterrestrial, or artificial. Examples include a total solar eclipse and a comet rendezvous.

A ring-shaped circumstellar disc of dust and debris, surrounding a star, that generates infrared radiation by the re-radiation of energy from the star’s hot interior. This re-radiation is most often due to stellar wind, but can also be triggered by magnetic activity and the collapse of a supernova. A debris disk may also be visible to the naked eye as a faint haze in the light of a variable star, or as an apparent feature in the light curve of a cataclysmic variable.

Any astronomical object that contains a large amount of hydrogen, helium, or other atomic elements with high densities compared to most ordinary atomic matter. This can be any astronomical body with a very high mass to radius ratio, including white dwarfs, neutron stars, and black holes. It can also refer to stellar remnants with very low radii, such as brown dwarfs.

The process by which the class of subatomic particles called baryons, consisting of protons and electrons, came into existence in the early Universe. It is the prevailing cosmological model for the origin of the observable Universe. The process is thought to have occurred through a phase transition from a highly dense state to the current expanding state. It is believed to have taken 13.8 billion years. This event is also referred to as the Big Bang. It is a key part of the theory of universal expansion.