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Astronomy Unit 2
| Term | Definition |
|---|---|
| Photosphere | the luminous visible surface of the sun, being a shallow layer of strongly ionized gases |
| Chromosphere | a gaseous envelope surrounding a star |
| Corona | a white or colored circle or set of concentric circles of light seen around a luminous body, especially around the sun or moon |
| Solar wind | an emanation from the sun's corona consisting of a flow of charged particles, mainly electrons and protons, that interacts with the magnetic field of the earth and other planetary bodies |
| Sunspot | one of the relatively dark patches that appear periodically on the surface of the sun and affect terrestrial magnetism and certain other terrestrial phenomena |
| Prominence | an eruption of a flamelike tongue of relatively cool, high-density gas from the solar chromosphere into the corona where it can be seen during a solar eclipse or by observing strong spectral lines in its emission spectrum |
| Solar Flare | a brief powerful eruption of particles and intense electromagnetic radiation from the sun's surface, associated with sunspots and causing disturbances to radio communication on earth Sometimes shortened to flare |
| Nuclear fusion | a reaction in which two nuclei combine to form a nucleus with the release of energy Sometimes shortened to fusion Compare nuclear fission See also thermonuclear reaction |
| Constellation | any of various groups of stars to which definite names have been given, as Ursa Major, Ursa Minor, Boötes, Cancer, Orion |
| Binary Star | a system of two stars that revolve about their common center of mass |
| Light Year | a very great distance, especially in development or progress |
| Apparent Magnitude | the magnitude of a star as it appears to an observer on the earth |
| Absolute Magnitude | the magnitude of a star as it would appear to a hypothetical observer at a distance of 10 parsecs or 32.6 light-years |
| Main Sequence Star | any star lying on a diagonal band that extends from hot stars of high luminosity to cool stars of low luminosity |
| Red Giant | a star in an intermediate stage of evolution, characterized by a large volume, low surface temperature, and reddish hue |
| Supergiant | an exceptionally luminous star whose diameter is more than 100 times that of the sun, as Betelgeuse or Antares |
| Nova | the star undergoing such an explosion |
| Hertzsprung-russell diagram | the graph showing the absolute magnitude plotted against the surface temperature for a group of stars. |
| Protostar | an early stage in the evolution of a star, after the beginning of the collapse of the gas cloud from which it is formed, but before sufficient contraction has occurred to permit initiation of nuclear reactions at its core. |
| Supernova | the star undergoing such an explosion |
| White dwarf | a star, approximately the size of the earth, that has undergone gravitational collapse and is in the final stage of evolution for low-mass stars, beginning hot and white and ending cold and dark |
| Neutron star | an extremely dense, compact star composed primarily of neutrons, especially the collapsed core of a supernova |
| Black hole | a theoretical massive object, formed at the beginning of the universe or by the gravitational collapse of a star exploding as a supernova, whose gravitational field is so intense that no electromagnetic radiation can escape. |
| Galaxy | a large system of stars held together by mutual gravitation and isolated from similar systems by vast regions of space |
| Big Bang Theory | a theory that deduces a cataclysmic birth of the universe (big bang) from the observed expansion of the universe, cosmic background radiation, abundance of the elements, and the laws of physics |
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