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Joshua Smith

astronomy pt2

TermDefinition
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.
Created by: 3082210