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Astronomy (Unit 2)

Vocab (definentions found by Dictionary.com and the textbook)

Astronomy The branch of science that deals with celestial objects, space, and the physical universe as a whole.
Geocentric Having or representing the earth as the center, as in former astronomical systems.
Heliocentric Having or representing the sun as the center, as in the accepted astronomical model of the solar system.
Retrograde Motion It is the apparent motion of a planet to move in a direction opposite to that of other bodies within its system, as observed from a particular vantage point. Direct motion or prograde motion is motion in the same direction as other bodies.
Ellipse A regular oval shape, traced by a point moving in a plane so that the sum of its distances from two other points (the foci) is constant, or resulting when a cone is cut by an oblique plane that does not intersect the base.
Astronomical Unit (AU) The mean distance between the Earth and the sun, about 98 million miles or 150 million kilometers.
Rotation The action of rotating around an axis or center
Revolution A forcible overthrow of a government or social order in favor of a new system.
Precession The slow movement of the axis of a spinning body around another axis due to a torque (such as gravitational influence) acting to change the direction of the first axis. It is seen in the circle slowly traced out by the pole of a spinning gyroscope.
Perihelion The point in the orbit of a planet, asteroid, or comet at which it is closest to the sun.
Aphelion The point in the orbit of a planet, asteroid, or comet at which it is furthest from the sun.
Peigree The point in the orbit of the moon or a satellite at which it is nearest to the earth.
Apogee The point in the orbit of the moon or a satellite at which it is furthest from the earth.
Phases of the moon The shape of the illuminated (sunlit) portion of the Moon as seen by an observer on Earth. The lunar phases change cyclically as the Moon orbits the Earth, according to the changing positions of the Moon and Sun relative to the Earth.
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 A large, bowl-shaped cavity in the ground or on the surface of a planet or the moon, typically one caused by an explosion or the impact of a meteorite or other celestial body.
Terrestrial planet A planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets are the inner planets closest to the Sun, i.e. Mercury, Venus, Earth, and Mars.
Jovian Planet The gas giant planets including Jupiter, Saturn, Uranus, and Neptune.
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.
Planetesimal A minute planet; a body that could or did come together with many others under gravitation to form a planet.
Asteroid A small rocky body orbiting the sun.
Comet A celestial object consisting of a nucleus of ice and dust and, when near the sun, a “tail” of gas and dust particles pointing away from the sun.
Coma A state of deep unconsciousness that lasts for a prolonged or indefinite period, caused especially by severe injury or illness.
Meteoroid A small body moving in the solar system that would become a meteor if it entered the earth's atmosphere.
Meteor A small body of matter from outer space that enters the earth's atmosphere, becoming incandescent as a result of friction and appearing as a streak of light.
Electromagnetic Spectrum The range of wavelengths or frequencies over which electromagnetic radiation extends.
Photon A particle representing a quantum of light or other electromagnetic radiation. A photon carries energy proportional to the radiation frequency but has zero rest mass
Spectroscopy The branch of science concerned with the investigation and measurement of spectra produced when matter interacts with or emits electromagnetic radiation
Doppler Effect An increase (or decrease) in the frequency of sound, light, or other waves as the source and observer move toward (or away from) each other. It causes the sudden change in pitch noticeable in a passing siren, as well as the redshift seen by astronomers.
Refracting Telescope A telescope that uses a converging lens to collect light.
Reflecting Telescope A telescope in which a mirror is used to collect and focus light
Radio Telescope An instrument used to detect radio emissions from the sky, whether from natural celestial objects or from artificial satellites.
Hubble Telescope It is a telescope launched into orbit around the earth in 1990 to provide information about the universe in the visible, infrared, and ultraviolet ranges Also called Hubble space telescope.
Space Shuttle a rocket-launched spacecraft, able to land like an unpowered aircraft, used to make repeated journeys between the earth and earth orbit.
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