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Rhodes Chapter 13
Stars and Galaxies
| Term | Definition |
|---|---|
| light-year | the distance light travels in one year |
| apparent magnitude (brightness) | a measure of how bright an object appears from Earth |
| luminosity (absolute brightness/magnitude) | the true brightness of an object |
| star | a large ball of gas held together by gravity with a core so hot that nuclear fusion occurs |
| radiative zone | a shell of cooler hydrogen above a star's core |
| convection zone | an area in a star where hot gas moves up toward the surface and cooler gas moves deeper into the interior |
| photosphere | the apparent surface of a star |
| chromosphere | the orange-red layer of a star above the photosphere |
| corona | the wide, outermost layer of a star's atmosphere |
| sunspots | regions of strong magnetic activity that are cooler than the rest of the photosphere and appear as dark splotches on the Sun |
| prominences | clouds of gas that make loops and jets extending into the corona |
| solar flares | violent eruptions of particles and radiation from the surface of the Sun |
| solar wind | charged particles that stream continually away from the Sun, can pass Earth, and extend into the solar system |
| Hertzsprung-Russell diagram (H-R diagram) | a graph that plots luminosity versus temperature of stars |
| main sequence star | a star that fuses hydrogen into helium in its core |
| giant star | a star with a much larger radius and luminosity than a main sequence star of the same surface temperature |
| white dwarf | forms as the core of a giant star no longer supports fusion and the star's outer layers escape into space, leaving a hot and dense core |
| nebula | a cloud of gas and dust that a star forms from |
| planetary nebula | forms after helium in a star's core is gone and it casts off its gases |
| supernova | an enormous explosion that destroys a star |
| black hole | an area in space that is so dense that nothing, including light, can escape its gravitational pull |
| galaxy | a huge collection of stars, gas, and dust |
| elliptical galaxy | a galaxy that has a generally spherical or oval shape and that has no apparent internal structure or spiral arms |
| irregular galaxy | a galaxy with no identifiable shape or structure |
| spiral galaxy | a galaxy exhibiting a central nucleus from which extend curved arms of higher luminosity |
| Milky Way galaxy | the spiral galaxy of which the Sun and the solar system are a part |
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erinrhodes
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