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Astronomy Part Two
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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 photosphere of the sun or another star. |
Corona | The rarefied gaseous envelope of the sun and other stars. |
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 | 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, as with radio frequency communications and power line transmissions. |
Aurora | A natural electrical phenomenon characterized by the appearance of streamers of reddish or greenish light in the sky, usually near the northern or southern magnetic pole. |
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 named after its apparent form or identified with a mythological figure |
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 |
Apparent Magnitude | The magnitude of a celestial object as it is actually measured from the earth. |
Absolute Magnitude | The magnitude of a celestial object as it would be seen at a standard distance of 10 parsecs. |
Main-Sequence Star | Any star that is fusing hydrogen in its core and has a 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. |
Supergiant | A very large star that is even brighter than a giant, often despite being relatively cool. |
Cepheid Variable | A variable star having a regular cycle of brightness with a frequency related to its luminosity, so allowing estimation of its distance from the earth. |
Nova | A star showing a sudden large increase in brightness and then slowly returning to its original state over a few months. |
Nebula | A cloud of gas and dust in outer space, visible in the night sky either as an indistinct bright patch or as a dark silhouette against other luminous matter. |
Hertzsprung-Russel Diagram | A two-dimensional graph, devised independently by Ejnar Hertzsprung and Henry Norris Russell, in which the absolute magnitudes of stars are plotted against their spectral types. |
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. |
Neutron Star | A celestial object of very small radius and very high density, composed predominantly of closely packed neutrons. |
Pulsar | A celestial object, thought to be a rapidly rotating neutron star, that emits regular pulses of radio waves and other electromagnetic radiation at rates of up to one thousand pulses per second. |
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. |
Hubble's Law | A law of cosmology stating that the rate at which astronomical objects in the universe move apart from each other is proportional to their distance from each other. |
Big Bang Theory | A theory that deduces a cataclysmic birth of the universe from the observed expansion of the universe, cosmic background radiation, abundance of the elements, and the laws of physics. |