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unit 2 vocabuulary
| Term | Definition |
|---|---|
| astronomy | the science that deals with the material universe beyond the earth's atmosphere. |
| geocentric | having or representing the earth as a center |
| heliocentric | measured or considered as being seen from the center of the sun. |
| retrograde motion | motion of a planet to move in a direction opposite to that of other bodies within its system. |
| ellipse | a plane curve such that the sums of the distances of each point in its periphery from two fixed points, the foci, are equal. |
| astronomical unit | a unit of length, equal to the mean distance of the earth from the sun. |
| rotation | the act of rotating; a turning around as on an axis. |
| revolution | an overthrow or repudiation and the thorough replacement of an established government or political system by the people governed. |
| precession | the act or fact of preceding; precedence. |
| perihelion | the point in the orbit of a planet or comet at which it is nearest to the sun. |
| aphelion | the point in the orbit of a planet or a comet at which it is farthest from the sun. |
| perigree | closet point to the earth and it is in this stage that the moon appears larger. |
| apogee | the point in the orbit of a heavenly body, especially the moon, or of a man-made satellite at which it is farthest from the earth. |
| phases of the moon | new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, third quarter and waning crescent. |
| solar eclipse | an eclipse in which the sun is obscured by the moon. |
| lunar eclipse | an eclipse in which the moon appears darkened as it passes into the earth's shadow. |
| crater | the cup-shaped depression or cavity on the surface of the earth or other heavenly body marking the orifice of a volcano. |
| terrestrial planet | inner planet |
| jovian planet | any of the four large outer planets: Jupiter, Saturn, Uranus, and Neptune. |
| nebula | any of the four large outer planets: Jupiter, Saturn, Uranus, and Neptune. |
| planetesimal | one of the small celestial bodies that, according to one theory (planetesimal hypothesis) were fused together to form the planets of the solar system. |
| asteroid | a small rocky body orbiting the sun. |
| comet | a celestial body moving about the sun, usually in a highly eccentric orbit, consisting of a central mass surrounded by an envelope of dust and gas that may form a tail that streams away from the sun. |
| coma | a state of prolonged unconsciousness, including a lack of response to stimuli, from which it is impossible to rouse a person. |
| meteoriod | any of the small bodies, often remnants of comets, traveling through space: when such a body enters the earth's atmosphere it is heated to luminosity and becomes a meteor. |
| meteor | a meteoroid that has entered the earth's atmosphere. |
| meteorite | a mass of stone or metal that has reached the earth from outer space; a fallen meteoroid. |
| electromagnetic spectrum | the entire spectrum, considered as a continuum, of all kinds of electric, magnetic, and visible radiation, from gamma rays having a wavelength of 0.001 angstrom to long waves having a wavelength of more than 1 million km. |
| photon | a quantum of electromagnetic radiation, usually considered as an elementary particle that is its own antiparticle and that has zero rest mass and charge and a spin of one. |
| spectroscopy | the science that deals with the use of the spectroscope and with spectrum analysis. |
| doppler effect | the shift in frequency of acoustic or electromagnetic radiation emitted by a source moving relative to an observer as perceived by the observer: the shift is to higher frequencies when the source approaches and to lower frequencies when it recedes. |
| refracting telescope | type of optical telescope that uses a lens as its objective to form an image. |
| reflecting telescope | an optical telescope which uses a single or combination of curved mirrors that reflect light and form an image. |
| radio telescope | a form of directional radio antenna used in radio astronomy |
| hubble telescope | space telescope that was launched into low earth orbit in 1990. |
| space shuttle | a rocket-launched spacecraft, able to land like an unpowered aircraft, used to make repeated journeys between the earth and earth orbit. |
| photosphere | a sphere of light or radiance. |
| chromosphere | a gaseous envelope surrounding a star. |
| corona | a white or colored circle or set of concentric circles of light seen around a luminous body, especially around the sun or moon. |
| solar wind | an emanation from the sun's corona consisting of a flow of charged particles, mainly electrons and protons, that interacts with the magnetic field of the earth and other planetary bodies. |
| sunspot | one of the relatively dark patches that appear periodically on the surface of the sun and affect terrestrial magnetism and certain other terrestrial phenomena. |
| prominence | the state of being prominent; conspicuousness. |
| 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 that revolve about their common center of mass. |
| light-year | a long distance or great amount |
| 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 at a distance of 10 parsecs or 32.6 light-years. |
| 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 star in an intermediate stage of evolution, characterized by a large volume, low surface temperature, and reddish hue. |
| supergiant | a very large star that is even brighter than a giant, often despite being relatively cool. |
| cepheid variable | a variable star in which changes in brightness are due to alternate contractions and expansions in volume. |
| nova | a star that suddenly becomes thousands of times brighter and then gradually fades to its original intensity. |
| 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 | the graph showing the absolute magnitude plotted against the surface temperature for a group of stars. |
| protostar | an early stage in the evolution of a star, after the beginning of the collapse of the gas cloud from which it is formed, but before sufficient contraction has occurred to permit initiation of nuclear reactions at its core. |
| supernova | explosive star |
| white dwarf | a star, approximately the size of the earth, that has undergone gravitational collapse and is in the final stage of evolution for low-mass stars, beginning hot and white and ending cold and dark. |
| neutron star | an extremely dense, compact star composed primarily of neutrons, especially the collapsed core of a supernova. |
| pulsar | one of several hundred known celestial objects, generally believed to be rapidly rotating neutron stars, that emit pulses of radiation, especially radio waves, with a high degree of regularity. |
| black hole | a theoretical massive object, formed at the beginning of the universe or by the gravitational collapse of a star exploding as a supernova, whose gravitational field is so intense that no electromagnetic radiation can escape. |
| galaxy | a large system of stars held together by mutual gravitation and isolated from similar systems by vast regions of space. |
| hubble's law | the law that the velocity of recession of distant galaxies from our own is proportional to their distance from us. |
| 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. |
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rachelarnold
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