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ch. 3
new book, lessons 2 - 6
| Term | Definition |
|---|---|
| solar system | The system consisting of the sun and the planets and other objects that revolve around it. |
| astronomical unit | a unit of distance equal to the average distance between Earth and the sun, about 150 kilometers. |
| planet | An object that orbits a star, is large enough to have become rounded by its own gravity, and has cleared the area of its orbit. |
| dwarf planet | An object that orbits the sun and is spherical, but has not cleared the area of its orbit. |
| planetesimal | One of the small asteroid-like bodies that formed the building blocks of the planets. |
| core | The central region of the sun, where nuclear fusion takes place. |
| nuclear fusion | The process in which two atomic nuclei combine to form a larger nucleus, forming a heavier element and releasing huge amounts of energy; the process by which energy is produced in stars. |
| radiation zone | A region of very tightly packed gas in the sun's interior where energy is transferred mainly in the form of electromagnetic radiation. |
| convection zone | the outermost layer of the sun's interior. |
| photosphere | The inner layer of the sun's atmosphere that gives off its visible light; the sun's surface. |
| chromosphere | The middle layer of the sun's atmosphere. |
| corona | The outer layer of the sun's atmosphere. |
| solar wind | A stream of electrically charged particles that emanate form the sun's corona. |
| sunspot | A dark area of gas on the sun's surface that is cooler than surrounding gas. |
| prominence | A huge, reddish loop of gas that protrudes from the sun's surface, linking parts of sunspot regions. |
| solar flare | an eruption of gas from the sun's surface that occurs when the loops in sunspot regions suddenly connect. |
| terrestrial planet | The name often given to the four inner planets: Mercury, Venus, Earth, and Mars. |
| greenhouse effect | The trapping of heat near a planet's surface by certain gases in the planet's atmosphere. |
| gas gaint | The name often given to the outer planets: Jupiter, Saturn |
| ring | A thin disk of small ice and rock particles surrounding a planet. |
| asteroid belt | The region of the solar system between the orbits of Mars and Jupiter, where many asteroids are found. |
| kuiper belt | A region where many small objects orbit the sun and that stretches from beyond the orbit of neptune to about 100 times Earth's distance from the sun. |
| Oort cloud | A spherical region of comments that surrounds the solar system. |
| comet | A loose collection of ice and dust that orbits the sun, typically in a long, narrow orbit. |
| coma | The fuzzy outer layer of a comet. |
| nucleus | The solid inner core of a comet. |
| asteroid | One of the rocky objects revolving around the sun that are too small and numerous to be considered planets. |
| meteoroid | A chunk of rock or dust in space, generally smaller than an asteroid. |
| meteor | A streak of light in the sky produced by the burning of a meteoroid in Earth's surface. |
| meteorite | A meteoroid that passes through the atmosphere and hits Earth's surface. |
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