Glossary
Astronomy glossary
514 definitions · page 2 of 9.
- Barnard's star
- a red dwarf in the constellation Ophiuchus that has the highest proper motion than any other known star; it was discovered by E. E. Barnard in 1916
- baryonic
- made up of baryons (elementary particles such as protons and electrons)
- baryonic matter
- "normal" matter composed of elementary particles called baryons
- baryons
- elementary particles such as protons and neutrons composed of three quarks
- baseline
- the line between two observational points or two telescopes of an interferometer
- Big Bang
- the giant explosion that is theorized to have created the universe 10 billion to 20 billion years ago
- billion
- 1,000,000,000 (in American usage)
- binary star
- a system of two stars that orbit a common center of gravity; also known as a double star
- binoculars
- a small, usually hand-held instrument with two tubes that is used to magnify the view of astronomical objects; the two numbers used to describe the binoculars refer to its magnification and its aperture in millimeters, respectively
- black hole
- a region of space where gravity is so powerful that not even light can escape; black holes can form either from the death of high-mass stars or in the cores of galaxies
- black holes
- regions of space where gravity is so powerful not even light can escape; black holes can form either from the death of high-mass stars or in the cores of galaxies
- blazar
- a high-energy, variable type of quasar which astronmers believe has a jet of material aimed in our direction that causes it to appear more energetic than other quasars
- blink comparator
- An instrument that allows astronomers to view two images of the same region of sky simultaneously. Objects that have changed their brightness or position appear to stand out of the plane of the picture.
- blueshift
- a decrease in the wavelength of light coming from an object due to its motion toward Earth
- Bok globule
- a small, dark nebula thought to be a region of star formation
- bolide
- a brilliant meteor or fireball that explodes in mid-air
- bolides
- brilliant meteors or fireballs that explode in mid-air
- Bose-Einstein condensate
- atoms crowded close together in ultra-low temperatures that behave as if they were one fluid-like superatom
- brown dwarf
- a gaseous object that forms like a star but lacks the necessary mass to sustain nuclear fusion in its core; a body intermediate in mass between a star and planet
- buckyball
- a naturally occurring form of carbon known as C-60, its molecular structure resembles the geodesic domes once designed by Buckminster Fuller
- bulge
- the generally spherical, central region of a spiral galaxy
- cannibal coronal mass ejections
- fast-moving solar eruptions that appear to overtake and often devour their slower-moving kin
- carbon star
- a red giant star with much more carbon than oxygen in its surface layers
- carbonaceous chondrites
- a class of stony meteorites and asteroids which contain organic (carbon) compounds and may be the most primitive samples of the early solar system
- Cassegrain telescope
- a reflecting telescope in which a secondary mirror reflects light back through a hole in the center of the primary mirror
- cataclysmic variable
- a close binary system which includes a white dwarf accreting matter from a less massive companion
- catadioptric telescope
- a telescope that combines the primary mirror of a reflector with a lens placed in front of the mirror that corrects for aberrations; most catadioptric telescopes for amateurs are Schmidt-Cassegrain telescopes
- CCD
- a silicon chip used to detect light; charge-coupled devices (CCDs) are far more efficient at collecting light than conventional film
- celestial pole
- the imaginary projection of Earth’s rotational axis onto the celestial sphere
- celestial sphere
- the apparent sphere of the sky; an imaginary sphere of immense radius centered on Earth often used to plot the coordinates of objects in the sky
- Cepheid variable
- a class of luminous stars that vary in brightness; used to calibrate distances to galaxies
- Chandrasekhar limit
- the maximum mass of a white dwarf star, equivalent to 1.4 solar masses
- charge-coupled device
- a silicon chip used to detect light; charge-coupled devices (CCDs) are far more efficient at collecting light than conventional film
- Charles Messier
- A French astronomer and comet hunter who discovered 13 comets independently and codiscovered a half-dozen others. While hunting for comets, Messier compiled a list of fuzzy objects that were not comets in order to avoid them. These catalog entries were later…
- chondrite
- a stony meteorite containing small, round, silicate granules called chondrules
- chromosphere
- a layer in a star’s atmosphere lying below the corona and above the photosphere
- circumpolar
- Circumpolar stars are permanently above the horizon from a given observing point on Earth; that is to say, they never set. At Earth's Geographical North Pole (90° north latitude), all stars in the sky are cirumpolar. On Earth's equator, no stars are…
- clock drive
- a motor attached to an equatorial mount that compensates for Earth’s rotation and thus keeps the telescope pointing at the same area of sky
- CME
- huge eruptions of electrified, magnetic gas ejected from the solar corona; this gas is hurled into space with speeds from 12 to 1,250 miles per second (about 20 to 2,000 kilometers per second); CMEs can produce geomagnetic storms and auroral displays on Earth
- coated optics
- optics treated with a thin, uniform coating that greatly reduces scattered light and thus makes the image brighter
- collapsar
- a giant star that collapses of its own weight at the end of its normal lifetime
- collimation
- the act of putting a telescope’s optics into perfect alignment
- coma
- the bright shroud of gas that surrounds a comet’s nucleus
- Coma Berenices
- A constellation between Bootes the Herdsman and Leo the Lion. Coma Berenices is an attractive swarm of stars known as Berenice's Hair.
- comet
- a small piece of ice and rock that orbits a star usually in a highly elongated orbit; long-period comets have orbital periods longer than 200 years, short-period comets have orbital periods less than 200 years
- comet nucleus
- a solid, compact mass of rock and ice that heats up when exposed to sunlight and releases gas and dust
- conjunction
- a time when two or more bodies appear close together in the sky
- constellation
- one of the 88 patterns of stars in the sky, often named for a mythological god, hero, or animal
- convection
- the transfer of heat energy by moving currents of material
- core
- the central region of a planet, brown dwarf, star, or galaxy
- corona
- the outer atmosphere of the sun or a star
- coronagraph
- an instrument designed to block light from the solar disk, allowing the corona to be observed
- coronagraphic mask
- an disk-shaped instrument designed to block light from the disk of a star, allowing the region very close to a target star to be studied
- coronal mass ejection
- a huge eruption of electrified, magnetic gas ejected from the solar corona; this gas is hurled into space with speeds from 12 to 1,250 miles per second (about 20 to 2,000 kilometers per second); CMEs can produce geomagnetic storms and auroral displays on Earth
- coronal mass ejections
- huge eruptions of electrified, magnetic gas ejected from the solar corona; this gas is hurled into space with speeds from 12 to 1,250 miles per second (about 20 to 2,000 kilometers per second); CMEs can produce geomagnetic storms and auroral displays on Earth
- cosmic background radiation
- microwave radiation that permeates the universe and represents the still-cooling heat generated from the Big Bang
- cosmic microwave background
- microwave radiation that permeates the universe and represents the still-cooling heat generated from the Big Bang
- cosmic ray
- an atomic nucleus (most are protons) moving at a speed approaching that of light
- cosmological constant
- a term in the equations of general relativity that represents a repulsive force in the universe
- cosmology
- the branch of science concerned with the structure and evolution of the universe