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Astronomy, Part 2
Term | Definition |
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Photosphere | the luminous envelope of a star from which its light and heat radiate. |
Chromosphere | a reddish gaseous layer immediately above the photoshere of the sun or another star. |
Corona | the rarefied gaseous envelope of the sun and other stars.The sun's corona is normally visible only during a total eclipse when it is seen as an irregular shaped pearly glow surrounding the darkened disk of the moon. |
Solar Wind | the continuous flow of charged particles from the sun that permeates the solar system. |
Sunspot | a spot or patch appearing from time to time on the sun's surface, appearing dark by contrast with its surroundings. |
Prominence | the state of being important or famous. |
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, as with radio frequency communication and power line transmissions. |
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 group of stars forming a recognizable pattern that is traditionally name after its apparent form or identified wih a mythological figure. Modern astronomers divide the sky into eighty-eight constellations with defined boundaries. |
Binary Star | a system of two stars in which one star revolves around the other or both revolve around a common center. |
Light-Year | a unit of astronomical distance equivalent to the distance that light travels in one year, which is 9.4607 × 1012 km (nearly 6 trillion miles). |
Apparent Magnitude | the magnitude of a celestial object as it is actually measured from the earth. |
Absolute Magnitude | the magnitude (brightness) of a celestial object as it would be seen at a standard distance of 10 parsecs. |
Main-sequence star | is any star that is fusing hydrogen in its core and has stable balance of outward pressure from core nuclear fusion and gravitational forces pushing inward. |
Red Giant | a very large star of high luminosity and low surface temperature. Red giants are thought to be in a late stage of evolution when no hydrogen remains in the core to fuel nuclear fusion. |
Supergiant | a very large star that is even brighter than a giant, often despite being relatively cool. |
Nova | a star showing a sudden large increase in brightness and then slowly returning to its original state over a few months. |
Hertzsprung-Russell Diagram | the graph showing the absolute magnitude plotted against the surface temperature for a group of stars. Also called H-R diagram. Origin of Hertzsprung-Russell diagram Expand. after Danish astronomer Ejnar Hertzsprung (1873-1967) and H. N. |
Protostar | a contracting mass of gas that represents an early stage in the formation of a star, before nucleosynthesis has begun. |
Supernova | a star that suddenly increases greatly in brightness because of a catastrophic explosion that ejects most of its mass. |
White Dwarf | a small very dense star that is typically the size of a planet. A white dwarf is formed when a low-mass star has exhausted all its central nuclear fuel and lost its outer layers as a planetary nebula. |
Neutron Star | a celestial object of very small radius (typically 18 miles/30 km) and very high density, composed predominantly of closely packed neutrons. |
Black Hole | a region of space having a gravitational field so intense that no matter or radiation can escape. |
Galaxy | a system of millions or billions of stars, together with gas and dust, held together by gravitational attraction. |
Big Bang Theory | The Big Bang theory is the prevailing cosmological model for the universe from the earliest known periods through its subsequent large-scale evolution. |