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Astronomy Part 2
Unit 2 Vocabulary
| Term | Definition |
|---|---|
| photosphere | the luminous visible surface of the sun,being a shallow layer of strongly ionized gases |
| chromosphere | a gaseous envelope surrounding the sun outside the photosphere, from which enormous quantities of hydrogen and other gases erupted |
| corona | a faintly luminous envelope outside the sun's chromosphere, the inner part consisting of highly ionized elements |
| solar wind | an emanation from the sun's corona consisting of a flow of charged particles that interacts with the magnetic field of the earth and other planets |
| sunspot | relatively dark patches that appears periodically on the surface of the sun |
| 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 eruption of intense high-energy radiation from the sun's surface, associated with sunspots and causing electromagnetic disturbances on the earth |
| nuclear fusion | a nuclear reaction in which atomic nuclei of low atomic number fuse to form a heavier nucleus with the release of energy |
| constellation | A grouping of stars on the celestial sphere perceived as a figure or design |
| binary star | A system of two stars bound together by gravity and orbiting a common center of mass, most often appearing as a single star when visible to the unaided eye |
| light-year | the distance traversed by light in one mean solar year, about 5.88 trillion mi.: used as a unit in measuring stellar distances |
| 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 from space |
| main-sequence star | any star lying on a diagonal band that extends from hot stars of high luminosity to cool stars of low luminosity; any stars in the Hertzsprung-Russell diagram from the upper left to the lower right of the diagram |
| red giant | star in an intermediate stage of evolution, characterized by a large volume, low surface temperature, and reddish hue. |
| supergiant | extremly large or powerful star |
| nova | a star that suddenly becomes thousands of times brighter and then gradually fades to its original intensity. |
| Hertzsprung- Russell Diagram | a graph in which the absolute magnitudes of stars are plotted against their spectral types. Stars are found to occupy only certain regions of such a diagram. |
| protostar | a large mass that forms by contraction of the gas of a giant molecular cloud in the interstellar medium |
| supernova | a stellar explosion that briefly outshines an entire galaxy |
| white dwarf | a stellar remnant composed mostly of electron-degenerate matter |
| neutron star | a type of compact star that can result from the gravitational collapse of a massive star after a supernova |
| black hole | a geometrically defined region of spacetime exhibiting such strong gravitational effects that nothing can escape from inside it. |
| galaxy | a system of millions or billions of stars held together by gravitational attraction. |
| 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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