Term Definition
Solar System the Sun, the planets and all the objects that orbit the Sun
planets the large bodies in space that orbit a star and do not produce its own light
orbit the path of an object as it circles around another object in outer space
moon a natural object that revolves around a planet
Earth the only planet in the solar system on which life is known to exist
satellite a natural object (such as a moon) or human built object (such as a communication satellite) that revolves around another object in space
comet a small object in space which orbits a star and is made of a rocky core surrounded by ice, dust particles, and frozen gases
Sun the star that is made of mostly hydrogen and helium gases, and supplies the heat and light that sustains life on Earth
meteor a piece of rock or metal from space (asteroids) that falls and enters Earth's atmosphere and burns up (also known as a falling star)
gravity an invisible force that pulls objects toward each other
revolution the movement of an object around another object or point; the trip that a planet takes around the Sun
atmosphere a layer of gases surrounding a planet
axis an imaginary straight line on which a planet rotates
tilt to slant or be in a sloping position; this causes the seasons on Earth
meteorite a meteor that hits the Earth
hemisphere half of the Earth
rotation the spinning motion of a planet on its axis as it revolves around the Sun
shuttle a two-way, re-usable space vehicle
space probes one-way space vehicles loaded with instruments to pursue science investigations in space
terrestrial another name for the inner planets
wane to decrease in size or intensity
wax to increase in size or intensity
star a body in space that gives off light like our Sun; the center of our solar system
astronomers a scientist who studies stars and other objects in space
space the area that reaches in all directions with no limit
gases matter that has the same form as air and can spread to fill all space open to them
universe all space and everything in it
asteroid belt the group of thousands of rocks that revolve around the Sun in an orbit between Mars and Jupiter
astronaut a person trained for traveling in space
telescope an optical instrument used for making distant objects appear closer and larger; used for looking at objects in outer space
lunar relating to the moon
constellation any of the 88 groups of stars as seen from Earth that represent animals, objects or mythological people

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