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Solar System iconSolar System
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asteroid — small, rocky body that orbits the sun. Most are located between Mars and Jupiter in a region called an asteroid belt; also called planetoids.

astronomy — study of celestial bodies, what they are made of and their magnitudes and motions.

atmosphere — the gases that surround a planet or moon, held in place by the force of gravity.

axis — imaginary line through poles of a planet, about which it rotates.

comet — body of ice and dust in orbit around the sun that develops a tail of ions and dust as it approaches the sun.

corona — sun?s outer part, visible as a halo during a total solar eclipse around the edge of the moon.

crater — bowl-shaped hole on a surface made by a volcanic explosion or the impact of a body such as a meteoroid.

density — measure of an object?s mass in relation to how much space it occupies.

eclipse — effect caused by one body casting a shadow on another. A solar eclipse occurs when the moon passes between the sun and Earth, casting a shadow on Earth. A lunar eclipse occurs when Earth passes between the sun and the moon, casting a shadow on the moon.

gas giants — largest four planets in the solar system (Jupiter, Saturn, Uranus, and Neptune) made largely of dense gaseous atmosphere.

geocentric — discredited theory that Earth is the center of the solar system.

gibbous phase — when a moon or planet shows more than half, but not all, of its face.

gravity — seeming force of attraction felt between two or more objects with mass.

heliocentric — theory that the sun is in the center of the solar system.

infrared — invisible part of light, with longer wavelengths that are felt as heat radiation.

light-year — distance light travels in a vacuum in one year, approximately 5.88 trillion miles

magnetosphere — magnetic field of a planet.

mass — measure of the amount of matter an object contains, not dependent on gravity.

meteor — mass of rock or metal that enters Earth?s atmosphere, usually burning up before reaching the planet?s surface.

meteorite — mass of rock or metal that has survived friction of Earth?s atmosphere to reach the surface.

meteoroid — dust and debris that travel through space and become meteors when they enter Earth?s atmosphere.

meteor shower — large number of meteors burning upon entering Earth?s atmosphere, occurring when Earth?s orbit passes through debris from a comet.

moon — natural satellite of a planet.

nebula — cluster of stars, or a cloud of dust particles and gases.

orbit — path followed by a star, planet, or satellite around a more massive body.

penumbra — outer and lighter part of the shadow created by an eclipse.

phase — size of the illuminated portion of a planet or moon.

pole — end of an axis, or the point where an axis meets the surface of a planet (geographic); either end of a magnet and points where the magnetic forces originate (magnetic).

planet — low-mass body that orbits a star.

rotation — turning around a center or an axis, or to turn in a circle.

satellite — small object, natural or artificial, that orbits a larger object.

solar flare — explosion on the sun?s surface causing a flaming arch millions of miles long, due to a shift in the sun?s magnetic field.

solar system — planets and bodies that orbit the sun and any group comprising a central star and orbiting planets.

solar wind — stream of charged particles emitted from the sun.

sunspot — darker and slightly cooler region on the surface of the sun, created when powerful magnetic fields stop the circulation of gases.

terrestrial — smallest planets in the solar system, made primarily of rock.

ultraviolet — powerful radiation, or energy, that has a wavelength shorter than light.

umbra — dark central zone created by an eclipse.

volume — amount of space an object occupies.

wane — decrease in the phase of a moon or planet.

wax — increase in the phase of a moon or planet.