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.

A

A-type star
absolute magnitude: A measure of a Template:Gli's absolute brightness. It is defined as the Template:Gli the star would show if it were located at a distance of 10 Template:Gli, or 32.6 Template:Gli.
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 Template:Gli displaying a much higher than normal Template:Gli over some part of the electromagnetic spectrum with characteristics indicating that the luminosity is not produced by Template:Gli. A galaxy hosting an AGN is called an active galaxy.
albedo: A measure of the proportion of the total solar radiation received by an Template:Gli, such as a Template:Gli, that is diffusely reflected away from the body.
aphelion: The point at which a body orbiting the Earth's Template:Gli is furthest from the Sun. Contrast Template:Gli.
apoapsis: The point at which an orbiting body is furthest from its Template:Gli. Contrast Template:Gli.
apogee: The point at which a body orbiting the Earth (such as the Template:Gli or an Template:Gli) is furthest from the Earth. Contrast Template:Gli.
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.
apsis: In the Template:Gli of a Template:Gli, one of the two extreme points of distance between the body and its Template:Gli – either the point of minimal distance, called the Template:Gli, or the point of maximal distance, called the Template:Gli. The term may also be used to refer to the value of the distance rather than the point itself. All Template:Gli have exactly two apsides.
argument of periapsis: The angle from an Template:Gli body's Template:Gli to its Template:Gli, measured in the direction of motion. It is one of six canonical Template:Gli used to characterize an orbit.
artificial satellite: An object that has been intentionally placed into Template:Gli by humans, often around the Earth but also around other bodies within the Template:Gli. Contrast Template:Gli.
ascending node: The Template:Gli at which an orbiting object moves north through the Template:Gli (in geocentric and heliocentric orbits) or at which the orbiting object moves away from the observer (in orbits outside of the Template:Gli). The position of the ascending node with respect to a reference direction, called the Template:Gli, is used along with other Template:Gli to describe an orbit. Contrast Template:Gli.
aspect: The position of a Template:Gli or Earth's Template:Gli with respect to the Template:Gli, as viewed from Earth.^[1]
asteroid: A Template:Gli of the inner Template:Gli, for example the one that orbits the Template:Gli at a distance is no greater than the orbit of Jupiter. Asteroids are somewhat arbitrarily distinguished from many different types of similar objects: Template:Gli primarily composed of dust and ice instead of mineral and rock are known as Template:Gli; bodies less than one meter in diameter are known as Template:Gli; very large asteroids are sometimes called Template:Gli or Template:Gli; and bodies similar to asteroids in size and composition but which lie beyond Jupiter are known as Template:Gli.
asteroid belt: The Template:Gli in the Template:Gli located roughly between the orbits of Mars and Jupiter that is occupied by numerous irregularly shaped Template:Gli ranging in size from dust particles to Template:Gli and Template:Gli. 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.
astrobiology: An interdisciplinary field that studies the origins, evolution, distribution, and future of living systems in the universe, encompassing research on organic compounds in Template:Gli, abiogenesis and extreme-environment adaptation on Earth, the habitability of Template:Gli, the possible existence of extraterrestrial life, and how humans might be able to detect extraterrestrial biosignatures, among other topics.
astrodynamics: See Template:Gli.
astrogeology
astrometric binary: A type of Template:Gli where evidence for an unseen orbiting companion is revealed by its periodic Template:Gli of the visible component. See also Template:Gli.
astrometry: The branch of astronomy that involves precise measurements of the positions and movements of Template:Gli and other Template:Gli.
astronomical body: A type of naturally occurring physical entity, association, or structure within the Template:Gli that is a single, tightly bound, contiguous structure, such as a Template:Gli, Template:Gli, Template:Gli, or Template:Gli. Though the terms astronomical "body" and Template:Gli are often used interchangeably, there are technical distinctions.
astronomical unit (AU): A unit of length used primarily for measuring astronomical distances within the Template:Gli or between the Earth and distant stars.
astronomy: The scientific study of Template:Gli and Template:Gli, the origins of those objects and phenomena, and their evolution.
astrophysics: The branch of astronomy that employs principles of physics and chemistry to determine the nature of Template:Gli 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 Template:Gli).
axial precession: A slow, continuous, gravity-induced change (a Template:Gli) in the orientation of an Template:Gli's Template:Gli.
axial tilt: The angle between an object's rotational axis and its orbital axis, or, equivalently, the angle between its Template:Gli plane and Template:Gli. Axial tilt usually does not change considerably during a single Template:Gli; Earth's axial tilt is the cause of the seasons. Axial tilt is distinct from Template:Gli.

B

barycenter: The common center of mass about which any two or more bodies of a gravitationally bound system Template:Gli.
baryogenesis: How 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 Template:Gli for the origin of the Template:Gli. 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 Template:Gli consisting of exactly two Template:Gli orbiting around their common Template:Gli. The term is often used interchangeably with Template:Gli, 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.

Glossary Of Astronomy Media

Syrtis Major (center) is a prominent dark Template:Gli on Mars.
Two bodies of similar mass orbit a common Template:Gli external to both, as usual in Template:Gli systems
A diagram of the relationships between the Earth's Template:Gli, its Template:Gli, and the Template:Gli around the Sun, known as the Template:Gli. Note that the Earth's rotational axis is not perpendicular to the ecliptic but rather is Template:Gli; this means that the path of the Sun, as viewed from Earth, appears to move both above and below the celestial equator during the course of the year.
Circumstellar Template:Gli as detected by the Hubble Space Telescope, and artist's impressions of the disks' orientations around their host stars
The Template:Gli (grey) is defined by the Earth's orbit around the Sun, and is distinct from the plane of the Template:Gli's Template:Gli (green), which is permanently Template:Gli 23.4 degrees with respect to the ecliptic. To an observer on Earth, this means that the path the Sun appears to follow upon the celestial sphere is not a straight line (i.e. the ecliptic does not appear "flat"). Twice during each complete orbit, at the two Template:Gli, the Sun's path appears to intersect the celestial equator, though the two planes are never in fact coplanar.
A relatively small body (such as a planet) orbiting a larger one (such as a star) in an Template:Gli, with the larger body located at one of the focal points of the ellipse
Sample Template:Gli for stars of different mass
A luminous red galaxy (LRG) acting as a Template:Gli, distorting the light from a much more distant blue galaxy into an Einstein ring
The Template:Gli are caused by the visible side of the Moon being alternately illuminated by sunlight and immersed in shadow during its orbit around the Earth.
The bright Template:Gli of the Template:Gli is visible in dark skies on clear nights, in the direction of the Template:Gli Sagittarius.

References

↑ Mitton, Jacqueline (2007). Cambridge Illustrated Dictionary of Astronomy. Cambridge, UK: Cambridge University Press. ISBN 978-0-521-82364-7.

[Mitton-1] Mitton, Jacqueline (2007). Cambridge Illustrated Dictionary of Astronomy. Cambridge, UK: Cambridge University Press. ISBN 978-0-521-82364-7.

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