Astronomy Definitions – Flashcards
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Planet
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An object that orbits one or more stars (and is not a star itself), is spherical, and does not share its orbit with another object.
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Satellite
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An artificial object or vehicle that orbits the earth, the moon, or other celestial bodies; also, a celestial body that orbits another body of larger size (for example, the moon is earth's natural satellite.
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Moon
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The natural satellite of the earth.
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Terrestrial Planet
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A planet that is composed primarily of silicate rocks or metals. The terrestrial planets are the inner planets closest to the Sun: Mercury, Venus, Earth, and Mars.
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Gas Giant Planet
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Gas giants have a mostly gaseous composition, such as hydrogen and helium. The four gas giants are (in order of distance from the Sun): Jupiter, Saturn, Uranus, and Neptune. They're larger than the 'inner' planets.
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Astronomical Unit (AU)
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The average distance between earth and the sun, about 150 x 10^6 km.
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Dwarf Planet
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A round, celestial object tat orbits around the sun; it may share its orbit with another celestial body, but it is not a satellite.
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Asteroid
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An object in space that ranges in size from a tiny speck, like a grain of sand, to 500km wide; most asteroids originate in the asteroid belt between Mars and Jupiter.
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Meteoroid
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A piece of rock moving through space.
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Meteor
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A meteoroid that hits Earth's atmosphere and burns up.
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Meteorite
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A meteoroid that is large enough to pass though Earth's atmosphere and reach the ground, without being totally burned up.
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Comet
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An object composed of rocky material, ice, and gas; comes from the Kuiper Belt or Oort Cloud.
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Revolution
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The time it takes for an object to orbit around another object; Earth's revolution around the sun is 365.24 days.
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Orbit
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The gravitationally curved path of an object about a point in space.
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Solar Eclipse
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The phenomenon in which the shadow of the Moon falls on Earth's surface.
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Lunar Eclipse
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The phenomenon in which the full Moon passes into Earth's shadow.
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Constellation
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A group of stars that seem to form a distinctive pattern in the sky.
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Nebula
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Giant cloud of gas and dust that is compressed to form a star.
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Neutron Star
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A star so dense that only neutrons can exist in its core.
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Supernova
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A massive explosion in which the entire outer portion of a star is blown off.
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Black Hole
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The remnant of a supernova explosion with a gravitational field so strong that nothing can escape its pull.
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Galaxy
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A huge collection of stars, planets, gas, and dust that is held together by gravity. Our galaxy is called the Milky Way.
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Rotation
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The turning of an object around an imaginary axis running through it; Earth's rotation around its axis is 24 hours.
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Similarities between inner and outer planets.
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They all follow an elliptical orbit, share the same orbital plane, and are spherical.
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Explain the Moon's relationship with the Earth.
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The Moon's gravity pulls on Earth's oceans and distorts them, causing tides.
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Phases of a lunar eclipse
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1. New Moon 2. Waxing Crescent 3. First Quarter 4. Waxing Gibbous 5. Full Moon 6. Waning Gibbous 7. Last Quarter 8. Waning Crescent 9. New Moon
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What causes seasons?
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The seasons are caused by the tilt of the Earth's rotational axis away or toward the sun as it travels through its year-long path around the sun
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Spiral Galaxies
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- Band of stars that make up a 'swirl'. - Usually have a 'bulge' in the middle. - There can be a bar of stars in the middle. - Have organization and structure, look 'flat'.
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Elliptical Galaxies
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- Can range in shape from a sphere to an oval, to oblong. - Houses some of the oldest stars in the universe.
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