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Joshua Smith
astronomy pt2
Term | Definition |
---|---|
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. Together with the corona, it constitutes the star's outer atmosphere. |
Corona | the rarefied gaseous envelope of the sun and other stars. The sun's corona is normally visible only during a total solar eclipse when it is seen as an irregularly 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 fact or condition of standing out from something by physically projecting or being particularly noticeable. |
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. 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 | the magnitude (brightness) of a celestial object as it would be seen at a standard distance of 10 parsecs. |
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. |
super giant | 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. |
nebulae | 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-russell diagram | a two-dimensional 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 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 and very high density, composed 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 | The Big Bang theory is the prevailing cosmological model for the universe from the earliest known periods through its subsequent large-scale evolution. |