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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.