| A | B |
|---|
| constellations | a grouping of stars that has a shape resembling an animal, mythological character, or other object and thus is named for it. |
| absolute magnitude | a measure of the amount of light a star or other space object gives off. |
| apparent magnitude | a measure of light received on Earth from an object in space. |
| parallax | the apparent shift in position of an object when viewed from two different points, such as your left eye and right eye. |
| light-year | a unit used to measure distance in space; the distance that light travels in one year (about 10 trillion km) |
| main sequence | on a Hertzsprung-Russell diagram, the diagonal band that includes 90 percent of all stars. |
| nebula | a large cloud of gas and dust in space that may be the beginning of a star. |
| giant | a late stage in a star's life cycle where the core has contracted and grown hotter, causing its outer layers to expand. |
| white dwarf | a late stage in a star's life cycle where its core runs out of fuel and its unstable outer layers excape into space, leaving the white-hot core. |
| supergiant | a late stage in the life cycle of a very large star, when the core reaches high temperatures, heavy elements form by fusion, and the star's outer layers expand. |
| neutron star | the final stage in the life cycle of some stars, where the core collapses and becomes so dense that only neutrons can exist there. |
| black hole | the final stage in the life cycle of some stars; the remnant of a star that is so dense that not even light can escape its gravity field. |
| photosphere | the innermost of the three layers of the sun's atmosphere; radiates the light we see. |
| chromosphere | the intermediate layer of the three layers of the sun's atmosphere, lying between the photosphere and the corona. |
| corona | the outermost and largest of the three layers of the sun's atmosphere, extending from the chromosphere outward millions of kilometers into space. |
| sunspot | a dark spot on the sun's surface that shows up because it is cooler than surrounding areas. |
| binary system | a system of two stars orbiting one another. |
| galaxy | a massive grouping of gas, dust , and stars in space; held together by gravity. |
| big bang theory | the leading theory of the origin of the universe. |
| extraterrestrial life | life that may exist in the universe outside of Earth. |
