Astronomy Ch 1
Terms
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- astronomical unit (AU)
- Average distance from Earth to the sun; 1.5 x 108 km, or 93 x 106 mi. (p. 6)
- galaxy
- A large system of stars, star clusters, gas, dust, and nebulae orbiting a common center of mass. (p. 8)
- light-year (ly)
- A unit of distance. The distance light travels in 1 year. (p. 7)
- Milky Way
- The hazy band of light that circles our sky. Produced by the glow of our galaxy. (p. 8)
- Milky Way Galaxy
- The spiral galaxy containing our sun. Visible in the night sky as the Milky Way. (p. 8)
- planet
- A small, nonluminous body formed by accretion in a disk around a protostar. (p. 6)
- scientific notation
- The system of recording very large or very small numbers by using powers of 10. (p. 6)
- solar system
- The sun and its planets, asteroids, comets, and so on. (p. 6)
- spiral arm
- Long spiral pattern of bright stars, star clusters, gas, and dust. Spiral arms extend from the center to the edge of the disk of spiral galaxies. (p. 8)
- star
- A globe of gas held together by its own gravity and supported by the internal pressure of its hot gases, which generate energy by nuclear fusion. (p. 6)