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| Term | Definition |
|---|---|
| solar system | the sun and all of the planets and other bodies that travel around it |
| heliocentric | sun-centered |
| parallax | an apparent shift in the position of an object when viewed from different locations |
| geocentric | describes something that uses Earth as the reference point |
| gravity | a force of attraction between objects that is due to their masses |
| orbit | the path that a body follows as it travels around another body in space |
| solar nebula | a rotating cloud of gas and dust from which the sun and planets formed |
| centripedal force | the inward force required to keep a particle or an object moving in a circular path |
| aphelion | in the orbit of a planet or other body in the solar system, the point that is farthest from the sun |
| perihelion | the point in the orbit of a planet at which the planet is closest to the sun |
| planetesimals | a small body from which a planet originated in the early stages of development of the solar system |
| nuclear fusion | the process by which nuclei of small atoms combine to form a new, more massive nucleus; the process releases energy |
| solar flare | flare an explosive release of energy that comes from the sun and that is associated with magnetic disturbances on the sun’s surface |
| prominence | a loop of relatively cool, incandescent gas that extends above the photosphere and above the sun’s edge as seen from Earth |
| sunspot | a loop of relatively cool, incandescent gas that extends above the photosphere and above the sun’s edge as seen from Earth |
| astronnomical unit | the average distance between Earth and the sun; approximately 150 million kilometers; symbol: AU |
| terrestrial planet | one of the highly dense planets nearest to the sun; Mercury, Venus, Mars, and Earth |
| gas giant | a planet that has a deep, massive atmosphere, such as Jupiter, Saturn, Uranus, or Neptune |
| planetery ring | a disk of matter that encircles a planet and consists of numerous particles in orbit, ranging in size from dust grains up to objects tens of meters across |
| meteor | a bright streak of light that results when a meteoroid burns up in Earth’s atmosphere |
| asteroids | a small, rocky object that orbits the sun; most asteroids are located in a band between the orbits of Mars and Jupiter |
| meteoroids | a relatively small, rocky body that travels through space |
| comet | a small body that gives off gas and dust as it passes close to the sun; a typical comet moves in an elliptical orbit around the sun and is made of dust and frozen gases |
| Kuiper belt | a region of the solar system that is just beyond the orbit of Neptune and that contains small bodies made mostly of ice |
| Oort cloud | a spherical region that surrounds the solar system, that extends from the Kuiper Belt to almost halfway to the nearest star, and that contains billions of comets |
| Kuiper belt object | one of the hundreds or thousands of minor planet-sized objects that orbit the sun in a flat belt beyond Neptune’s orbit |
| dwarf planet | a celestial body that orbits the sun, is round because of its own gravity, but has not cleared its orbital path |
| metoerite | a meteoroid that reaches Earth’s surface without burning up completely |