| A | B |
|---|
| solar system | the system composed of the sun (a star) and the planets, asteroids, comets, and meteors that travel around the sun |
| planetesimal | the tiny building blocks of the planets that formed as dust particles stuck together and grew in size |
| rotation | the spinning motion of a body on its axis |
| orbit | the elliptical path a body takes as it travels around another body in space |
| revolution | the elliptical motion of a body as it orbits another body in space |
| ellipse | a closed curve in which the sum of the distances from the edge of the curve to two points inside the ellipse is always the same |
| astronomical unit | the average distance between the Earth and the Sun, approximately 150,000,000 km |
| terrestrial planets | the small, dense, rocky planets of the inner solar system |
| satellite | a natural or artificial body that revolves around a planet |
| comet | a small body of ice and rock that gives off gas and dust in the form of a tail as it passes close to the sun |
| asteroid | a small, rocky body that revolves around the sun |
| asteroid belt | the region of the solar system most asteroids occupy, roughly between the orbits of Mars and Jupiter |
| meteoroid | a very small, rocky body the revolves around the sun |
| meteorite | a meteoroid that reaches the Earth’s surface without burning up completely |
| meteor | a streak of light caused when a meteoroid or comet dust burns up in the Earth’s atmosphere before it reaches the ground |
| nebula | a large cloud of dust and gas in interstellar space |
