Astronomy, ARI-BRA
Human beings have long been fascinated by the celestial sphere above, whose twinkling lights have inspired not only scientific theories but also many artistic endeavors. Humankind's fascination with the world beyond Earth has led to many landmark moments in history, as when space exploration took a giant step forward with the advent of technology that allowed humans to successfully travel to the Moon and to build spacecraft capable of exploring the rest of the solar system and beyond.
Astronomy Encyclopedia Articles By Title
Ariel
Ariel, second nearest of the five major moons of Uranus. It was discovered in 1851 by William Lassell, an English......
Aries
Aries, in astronomy, zodiacal constellation in the northern sky lying between Pisces and Taurus, at about 3 hours......
Aristarchus of Samos
Aristarchus of Samos was a Greek astronomer who maintained that Earth rotates on its axis and revolves around the......
Armillary sphere
Armillary sphere, early astronomical device for representing the great circles of the heavens, including in the......
Armstrong, Neil
Neil Armstrong was a U.S. astronaut, and the first person to set foot on the Moon. Neil Armstrong was the eldest......
Arp, Halton Christian
Halton Christian Arp was an American astronomer noted for challenging the theory that redshifts of quasars indicate......
Arrest, Heinrich Louis d’
Heinrich Louis d’Arrest was a German astronomer who, while a student at the Berlin Observatory, hastened the discovery......
Artemis
Artemis, U.S. crewed spaceflight program begun in 2017 that is intended to return astronauts to the surface of......
Artemis Accords
Artemis Accords, set of principles and nonbinding agreements to guide international cooperation in space exploration.......
Artemis II
Artemis II, U.S. space mission, launched on April 1, 2026, and successfully concluded on April 10. It was the first......
Artemis III
Artemis III, U.S. spaceflight that will launch in 2027 and test lunar landers in Earth orbit in preparation for......
Aryabhata
Aryabhata, first unmanned Earth satellite built by India. It was named for a prominent Indian astronomer and mathematician......
Aryabhata
Aryabhata was an astronomer and the earliest Indian mathematician whose work and history are available to modern......
Association of Universities for Research in Astronomy
Association of Universities for Research in Astronomy (AURA), consortium of U.S. universities that directs the......
Asterism
Asterism, a pattern of stars that is not a constellation. An asterism can be part of a constellation, such as the......
Asteroid
Asteroid, any of a host of small bodies, about 1,000 km (600 miles) or less in diameter, that orbit the Sun primarily......
astrobiology
astrobiology, a multidisciplinary field dealing with the nature, existence, and search for extraterrestrial life......
astrolabe
astrolabe, any of a type of early scientific instrument used for reckoning time and for observational purposes.......
astronaut
astronaut, designation, derived from the Greek words for “star” and “sailor,” commonly applied to an individual......
Astronomical map
Astronomical map, any cartographic representation of the stars, galaxies, or surfaces of the planets and the Moon.......
Astronomical observatory
Astronomical observatory, any structure containing telescopes and auxiliary instruments with which to observe celestial......
Astronomical unit
Astronomical unit (AU, or au), a unit of length effectively equal to the average, or mean, distance between Earth......
Astronomy
Astronomy, science that encompasses the study of all extraterrestrial objects and phenomena. Until the invention......
- Introduction
- Solar System, Planets, Stars
- Asteroids, Comets, Meteors
- Extrasolar, Planetary, Systems
- Star Formation, Evolution, Processes
- Galactic Centre, Observations, Stars
- Cosmology, Universe, Stars
- Techniques, Observations, Measurements
- Multi-Messenger, Gravitational Waves, Neutrinos
- Ancient, Celestial, Observations
- Ancient Greece, Stars, Planets
- India, Islamic, Medieval
- Copernicus, Heliocentric, Revolution
- Enlightenment, Celestial Bodies, Observations
- Herschel, Milky Way, Stars
- Stars, Galaxies, Cosmology
- Relativity, Space-Time, Cosmology
- Galaxies, Expansion, Universe
- Steady State, Cosmology, Big Bang
- Satellite, Observatories, Exploration
Astrophysics
Astrophysics, branch of astronomy concerned primarily with the properties and structure of cosmic objects, including......
Atacama Large Millimeter Array
Atacama Large Millimeter Array (ALMA), radio telescope system located on the Chajnantor plateau in Chile’s Atacama......
Ataxite
Ataxite, any iron meteorite containing more than 16 percent nickel. Ataxites, containing taenite as their main......
Atlas
Atlas, series of American launch vehicles, designed originally as intercontinental ballistic missiles (ICBMs),......
Aton
Aton, in ancient Egyptian religion, a sun god, depicted as the solar disk emitting rays terminating in human hands,......
Atum
Atum, in ancient Egyptian religion, one of the manifestations of the sun and creator god, perhaps originally a......
Auriga
Auriga, constellation in the northern sky, at about 6 hours right ascension and 45° north in declination. The brightest......
Automated Transfer Vehicle
Automated Transfer Vehicle (ATV), uncrewed European Space Agency (ESA) spacecraft that carried supplies to the......
Automatic picture transmission station
Automatic picture transmission station, in meteorology, any of several hundred installations, located in most of......
Autumnal equinox
Autumnal equinox, two moments in the year when the Sun appears exactly above the Equator; also, either of the two......
Auwers, Arthur von
Arthur von Auwers was a German astronomer known for his star catalogs. After receiving a Ph.D. in astronomy (1862)......
avoidance, Zone of
Zone of avoidance, region characterized by an apparent absence of galaxies near the plane of the Milky Way Galaxy......
azimuth
azimuth, the angular distance from the north or south point of the horizon to the foot of the vertical circle through......
Babcock, Harold Delos
Harold Delos Babcock was an astronomer who, with his son Horace Welcome Babcock, invented (1951) the solar magnetograph,......
Babcock, Horace Welcome
Horace Welcome Babcock was an American astronomer who, with his father, Harold Delos Babcock, invented the solar......
Bacon, Henry
Henry Bacon was an American architect, best-known as the designer of the Lincoln Memorial and the Reflecting Pool......
Bacon, Roger
Roger Bacon was an English Franciscan philosopher and educational reformer who was a major medieval proponent of......
Bailly, Jean-Sylvain
Jean-Sylvain Bailly was a French statesman noted for his role in the French Revolution, particularly in leading......
Baily, Francis
Francis Baily was an astronomer who detected the phenomenon called “Baily’s beads” during an annular eclipse of......
Baily’s beads
Baily’s beads, arc of bright spots seen during total and annular eclipses of the Sun. They are named for Francis......
Bainbridge, John
John Bainbridge was an astronomer noted for his observations of comets. Bainbridge practiced medicine at Ashby-de-la-Zouch......
Banneker, Benjamin
Benjamin Banneker was a mathematician, astronomer, compiler of almanacs, inventor, and writer, one of the first......
Barnard, Edward Emerson
Edward Emerson Barnard was an astronomer who pioneered in celestial photography and who was the leading observational......
Barnard’s star
Barnard’s star, second nearest star to the Sun (after the triple system of Proxima Centauri and Alpha Centauri’s......
Barron, Kayla
Kayla Barron is an American astronaut who spent six months on the International Space Station (ISS) from November......
Barrow, John D.
John D. Barrow was a British astrophysicist who received the 2006 Templeton Prize for Progress Toward Research......
Battānī, al-
al-Battānī was an Arab astronomer and mathematician who refined existing values for the length of the year and......
Bayer, Johann
Johann Bayer was a German astronomer whose book Uranometria promulgated a system of identifying all stars visible......
Bean, Alan
Alan Bean was an American astronaut and lunar module pilot on the Apollo 12 mission (November 14–22, 1969), during......
Beer, Wilhelm
Wilhelm Beer was a German banker and amateur astronomer who (with Johann Heinrich von Mädler) constructed the most......
Bell Burnell, Jocelyn
Jocelyn Bell Burnell is a British astronomer who discovered pulsars, the cosmic sources of peculiar radio pulses.......
Bella, Ivan
Ivan Bella is a Slovak pilot and air force officer and the first Slovak citizen to go into space. Bella graduated......
Bellatrix
Bellatrix, the 26th brightest star in the sky and the third brightest star in the constellation of Orion. Bellatrix......
Belyayev, Pavel
Pavel Belyayev was a cosmonaut who served as the commander of the Voskhod 2 spacecraft during the Soviet Union’s......
Bendis
Bendis, Thracian goddess of the moon; the Greeks usually identified her with the goddess Artemis. She is often......
Bessel, Friedrich Wilhelm
Friedrich Wilhelm Bessel was a German astronomer whose measurements of positions for about 50,000 stars and rigorous......
Beta Centauri
Beta Centauri, second brightest star (after Alpha Centauri) in the southern constellation Centaurus and the 10th......
Beta Crucis
Beta Crucis, second brightest star (after Alpha Crucis) in the southern constellation Crux (the Southern Cross)......
Beta Lyrae
Beta Lyrae, eclipsing binary star, the two component stars of which are so close together that they are greatly......
Beta Pictoris
Beta Pictoris, fourth-magnitude star located 63 light-years from Earth in the southern constellation Pictor and......
Betelgeuse
Betelgeuse, second brightest star in the constellation Orion, marking the eastern shoulder of the hunter. Its name......
Bethe, Hans
Hans Bethe was a German-born American theoretical physicist who helped shape quantum physics and increased the......
Bethlehem, Star of
Star of Bethlehem, celestial phenomenon mentioned in the Gospel According to Matthew as leading “wise men from......
Bhaskara I
Bhaskara I was an Indian astronomer and mathematician who helped to disseminate the mathematical work of Aryabhata......
Biela, Wilhelm, Freiherr von
Wilhelm, Freiherr von Biela was an Austrian astronomer who is noted for his discovery (1826) that a certain comet,......
Biela’s Comet
Biela’s Comet, short-period comet named for the Austrian astronomer Wilhelm, Freiherr (baron) von Biela (1782–1856).......
Big Dipper, The
The Big Dipper, asterism of the seven bright stars in the larger constellation Ursa Major. The two stars at the......
Big-bang model
Big-bang model, widely held theory of the evolution of the universe. Its essential feature is the emergence of......
Binary star
Binary star, pair of stars in orbit around their common centre of gravity. A high proportion, perhaps one-half,......
Biosatellite
Biosatellite, any of a series of three U.S. Earth-orbiting scientific satellites designed to study the biological......
Black hole
Black hole, cosmic body of extremely intense gravity from which nothing, not even light, can escape. A black hole......
blackbody radiation
blackbody radiation, energy radiated by any object or system that absorbs all incident radiation. The term usually......
Bliss, Nathaniel
Nathaniel Bliss was Britain’s fourth Astronomer Royal. Bliss graduated from Pembroke College, Oxford (B.A., 1720;......
Blue moon
Blue moon, the second full moon in a calendar month. The period from one full moon to another is about 29 12 days,......
Blue Origin
Blue Origin, the American aerospace company founded in 2000 by billionaire tech entrepreneur Jeff Bezos, was the......
Blue straggler star
Blue straggler star, star of bluish colour (and thus hot) that is found in old star clusters and that appears to......
Bluford, Guion
Guion Bluford is an astronaut who was the first African American launched into space. Bluford received an undergraduate......
Bode, Johann Elert
Johann Elert Bode was a German astronomer best known for his popularization of Bode’s law, or the Titius-Bode rule,......
Bode’s law
Bode’s law, empirical rule giving the approximate distances of planets from the Sun. It was first announced in......
Boeing Company
Boeing is an American aerospace manufacturer and a leading producer of commercial aircraft. It also produces military......
Bok, Bart J.
Bart J. Bok was a Dutch-born American astronomer known for his work on the structure and evolution of the Milky......
Bolden, Charles
Charles Bolden is an American astronaut who served as the first African American administrator of the National......
Bond, William Cranch
William Cranch Bond was an American astronomer who, with his son George Phillips Bond (1825–65), discovered Hyperion,......
Bondar, Roberta
Roberta Bondar is a Canadian neurologist, researcher, and astronaut. She was the first Canadian woman and the first......
Bondi, Sir Hermann
Sir Hermann Bondi was an Austrian-born British mathematician and cosmologist who, with Fred Hoyle and Thomas Gold,......
Bonner Durchmusterung
Bonner Durchmusterung (BD), star catalog showing the positions and apparent magnitudes of 324,188 northern stars.......
Borda, Jean-Charles de
Jean-Charles de Borda was a French mathematician and nautical astronomer noted for his studies of fluid mechanics......
Borman, Frank
Frank Borman was a U.S. astronaut who, in Apollo 8 with James A. Lovell and William A. Anders in December 1968,......
Boscovich, Ruggero Giuseppe
Ruggero Giuseppe Boscovich was an astronomer and mathematician who gave the first geometric procedure for determining......
Boss, Lewis
Lewis Boss was an American astronomer best known for his compilation of star catalogs. Boss worked for the U.S.......
Bouguer, Pierre
Pierre Bouguer was a versatile French scientist best remembered as one of the founders of photometry, the measurement......
Bouvard, Alexis
Alexis Bouvard was an astronomer and director of the Paris Observatory, who is noted for discovering eight comets......
Bowditch, Nathaniel
Nathaniel Bowditch was a self-educated American mathematician and astronomer, author of the best American book......
Bowen, I.S.
I.S. Bowen was an American astrophysicist whose explanation of the strong green emission from nebulae (clouds of......
Boötes
Boötes, constellation in the northern sky, at about 15 hours right ascension and 30° north in declination. The......
Bradley, James
James Bradley was an English astronomer who in 1728 announced his discovery of the aberration of starlight, an......
Brahe, Tycho
Tycho Brahe was a Danish astronomer whose work in developing astronomical instruments and in measuring and fixing......