Research Rack: Glossary

galaxy - a massive grouping of gas, dust, and stars in space held together by gravity

giant star - a late stage in a star’s life cycle in which the core has contracted and grown hotter, causing its outer layers to expand

inner planets - the four solid, rocky planets closest to the Sun, Mercury, Venus, Earth, and Mars

iron - a heavy malleable ductile magnetic silver-white metallic element that readily rusts in moist air, occurs native in meteorites and combined in most igneous rocks, is the most used of metals, and is vital to biological processes

light-year - a unit of length in astronomy equal to the distance that light travels in one year or 9,458,000,000,000 kilometers

morph - a local population of a species that consists of interbreeding organisms and is distinguishable from other populations by morphology or behavior though capable of interbreeding with them

navigation - the science of getting ships, aircraft, or spacecraft from place to place; especially the method of figuring out position, course, and distance traveled

nebula - a large cloud of gas and dust in space that is the beginning of a star
outer planets - the five planets farthest from the Sun—Jupiter, Saturn, Uranus, Neptune, Pluto.

planet - a heavenly body other than a comet, asteroid, or satellite that travels in orbit around the Sun; also such a body orbiting another star

plasma - a collection of charged particles (as in the atmospheres of stars) that shows some characteristics of a gas but that differs from a gas in being a good conductor of electricity and in being affected by a magnetic field

propulsion - the action of pushing or driving, usually forward or onward

radiation - the combined processes of emission, transmission, and absorption of radiant energy

satellite - any object that revolves around another object

solar flare - a sudden temporary outburst of energy from a small area of the sun's surface -also called flare

solar system - a star with the group of heavenly bodies that revolve around it; especially the Sun with the planets, asteroids, comets, and meteors that orbit it

star - a ball-shaped gaseous celestial body (such as the Sun) of great mass that shines by its own light