| A | B |
|---|
| asteroid | a small, rocky object that orbits the sun, usually in a band between the orbits of Mars and Jupiter |
| asteroid belt | the region of hte solar system that is between the orbits of Mars and Jupiter and in which most asteroids orbit |
| astronomical unit | the average distance between the Earth and the sun; approximately 150 million kilometers (symbol AU) |
| comet | a small body of ice, rock, and cosmic dust that follows an elliptical orbit around the sun and that gives off gas and dust in the form of a tail as it passes close to the sun |
| eclipse | an event in which the shadow of one celestial body falls on another |
| gas giant | a planet that has a deep, massive atmosphere, such as Jupiter, Saturn, Uranus or Neptune |
| meteor | a bright streak of light that results when a meteroid burns up in the Earth's atmosphere |
| meteorite | a meteoroid that reaches the Earth's surface without burning up completely |
| meteoroid | a relatively small, rocky body that travels through space |
| NASA | the National Aeronautics and Space Administration |
| nuclear fusion | the combination of the nuclei of small atoms to form a larger nucleus; releases energy |
| orbit | the path that a body follows as it travels around another body in space |
| phase | the change in the sunlit area of one celestial body as seen from another celestial body |
| prograde motion | the counterclockwise spin of a planet or moon as seen from above the planet's North Pole; rotation in the same direction as the sun's rotation |
| rocket | a machine that uses escaping gas from burning fuel to move |
| retrograde motion | the clockwise spin of a planet or moon as seen from above the planet's North Pole |
| revolution | the motion of a body that travels around another body in space; one complete trip around an orbit |
| rotation | the spin of a body on its axis |
| satellite | a natural or artificial body that revolves around a planet |
| solar nebula | the cloud of gas and dust that formed our solar system |
| space probe | an uncrewed vehicle that carries scientific instruments into space to collect scientific data |
| space shuttle | a reusable space vehicle that takes off like a rocket and lands like an airplane |
| space station | a long-term orbiting platform from which other vehicles can be launched or scientific research can be carried out |
| sunspot | a dark area of the photosphere of the sun that is cooler than the surrounding area and that has a strong magnetic field |
| terrestrial planet | one of the highly dense planets nearest to the sun; Mercury, Venus, Mars and Earth |
