Glossary of astronomy
This glossary of astronomy is a list of definitions of terms and concepts relevant to Astronomy and Cosmology. with their related fields, Astronomy is involved with the study of celestial objects and phenomena originate outside the atmosphere of Earth.
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- A-type star
- absolute magnitude
- A measure of a 's absolute brightness. It is defined as the the star would show if it were located at a distance of 10 , or 32.6 .
- accretion disk
- A roughly circular mass of diffuse material in orbit around a central object, such as a star or black hole. The material is acquired from a source external to the central object, and friction causes it to spiral inward towards the object.
- active galactic nucleus (AGN)
- A compact region in the center of a displaying a much higher than normal over some part of the electromagnetic spectrum with characteristics indicating that the luminosity is not produced by . A galaxy hosting an AGN is called an active galaxy.
- A measure of the proportion of the total solar radiation received by an , such as a , that is diffusely reflected away from the body.
- The point at which a body orbiting the Earth's is furthest from the Sun. Contrast .
- The point at which an orbiting body is furthest from its . Contrast .
- The point at which a body orbiting the Earth (such as the or an ) is furthest from the Earth. Contrast .
- apparent magnitude
- A measure of the brightness of a celestial body as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere. The brighter the object appears, the lower its magnitude.
- In the of a , one of the two extreme points of distance between the body and its – either the point of minimal distance, called the , or the point of maximal distance, called the . The term may also be used to refer to the value of the distance rather than the point itself. All have exactly two apsides.
- argument of periapsis
- The angle from an body's to its , measured in the direction of motion. It is one of six canonical used to characterize an orbit.
- artificial satellite
- An object that has been intentionally placed into by humans, often around the Earth but also around other bodies within the . Contrast .
- ascending node
- The at which an orbiting object moves north through the (in geocentric and heliocentric orbits) or at which the orbiting object moves away from the observer (in orbits outside of the ). The position of the ascending node with respect to a reference direction, called the , is used along with other to describe an orbit. Contrast .
- The position of a or Earth's with respect to the , as viewed from Earth.
- A of the inner , for example the one that orbits the at a distance is no greater than the orbit of Jupiter. Asteroids are somewhat arbitrarily distinguished from many different types of similar objects: primarily composed of dust and ice instead of mineral and rock are known as ; bodies less than one meter in diameter are known as ; very large asteroids are sometimes called or ; and bodies similar to asteroids in size and composition but which lie beyond Jupiter are known as .
- asteroid belt
- The in the located roughly between the orbits of Mars and Jupiter that is occupied by numerous irregularly shaped ranging in size from dust particles to and . The asteroid belt is often called the main asteroid belt or main belt to distinguish it from other asteroid populations in other parts of the Solar System.
- An interdisciplinary field that studies the origins, evolution, distribution, and future of living systems in the universe, encompassing research on organic compounds in , abiogenesis and extreme-environment adaptation on Earth, the habitability of , the possible existence of extraterrestrial life, and how humans might be able to detect extraterrestrial biosignatures, among other topics.
- See .
- astrometric binary
- A type of where evidence for an unseen orbiting companion is revealed by its periodic of the visible component. See also .
- The branch of astronomy that involves precise measurements of the positions and movements of and other .
- astronomical body
- A type of naturally occurring physical entity, association, or structure within the that is a single, tightly bound, contiguous structure, such as a , , , or . Though the terms astronomical "body" and are often used interchangeably, there are technical distinctions.
- astronomical unit (AU)
- A unit of length used primarily for measuring astronomical distances within the or between the Earth and distant stars.
- The scientific study of and , 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 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 ).
- axial precession
- A slow, continuous, gravity-induced change (a ) in the orientation of an 's .
- axial tilt
- The angle between an object's rotational axis and its orbital axis, or, equivalently, the angle between its plane and . Axial tilt usually does not change considerably during a single ; Earth's axial tilt is the cause of the seasons. Axial tilt is distinct from .
- The common center of mass about which any two or more bodies of a gravitationally bound system .
- The process by which the class of subatomic particles known as baryons were generated in the early Universe, including the means by which baryons outnumber antibaryons.
- Big Bang
- The prevailing for the origin of the . It depicts a starting condition of extremely high density and temperature, followed by an ongoing expansion that led to the current conditions.
- binary star
- A consisting of exactly two orbiting around their common . The term is often used interchangeably with , though the latter can also refer to an optical double star, a type of optical illusion which is entirely distinct from true binary star systems.
|The Simple English Wiktionary has a definition for: scale, friction, spiral, inward, and luminosity.|
|The Simple English Wiktionary has a definition for: contrast, magnitude, node, and canonical.|
|The Simple English Wiktionary has a definition for: distinguish, arbitrarily, diameter, composition, and beyond.|
|The Simple English Wiktionary has a definition for: interdisciplinary and extraterrestrial.|
|The Simple English Wiktionary has a definition for: structure, entity, natural, contiguous, and interchangeable.|
|The Simple English Wiktionary has a definition for: distinction, examinine, induce, orientation, and equivalent.|
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|The Simple English Wiktionary has a definition for: outnumber and particle.|