| Term | Definition |
|---|
| big bang | the initial explosion that resulted in the expansion of the universe |
| irregular galaxy | a galaxy that doesn't have a regular shape |
| elliptical galaxy | a galaxy that is shaped like a flattened ball with only old stars |
| spiral galaxy | a galaxy whose arms curve outward in a pinwheel pattern |
| eclipsing binary | a star system in which one star periodically blocks the other |
| binary star | a star system that contains two stars |
| quasar | a distant galaxy with a black hole at its center |
| black hole | the remains of an extremely massive star pulled into a small volume by the force of gravity |
| supernova | the explosion of a giant or supergiant star |
| neutron star | a tiny star that remains after a supernova explosion |
| white dwarf | the remaining hot core of a star after its outer layers have expanded and drifted out into space |
| protostar | a contracting cloud of gas and dust; the earliest stage of a star's life |
| nebula | a large amount of gas and dust in space, spread out in an immense volume |
| pulsar | a neutron star that produces radio waves |
| main sequence | an area on the Hertzsprung-Russel diagram that runs from lower left to lower right and includes more then 90% of all stars |
| HR diagram | a graph relating to the temperature and brightness of stars |
| absolute magnitude | the brightness of a star if it were a standard distance from Earth |
| apparent magnitude | the brightness of a star as seen from Earth |
| giant star | a very large star, much larger than the sun |
| parallax | the apparent change in position of an object when seen from different places |
| light-year | the distance light travels in one year |
| universe | all of space and everything in it |
| galaxy | a giant structure that contains hundreds of billions of stars |
| observatory | a building that contains one or more telescopes |
| constellation | a pattern of stars in the sky |
| astronomy | the study of the moon, stars, and other objects in space |
| axis | an imaginary line that passes through Earth's center and the North and South poles, about which Earth rotates |
| rotation | the spinning motion of a planet about its axis |
| revolution | the movement of an object around another object |
| orbit | the path of an object as it revolves around another in space |
| solstice | the two days of the year on which the noon sun is directly overhead at either 23.5 degress North or 23.5 degrees South |
| equinox | the two days of the year on which neither hemisphere is tilted toward or away from the sun |
| vernal equinox | the day of the year that marks the beginning of spring in the Northern Hemisphere |
| autumnal equinox | the day of the year that marks the beginning of fall in the Northern Hemisphere |
| phase | one of the different shapes of the moon as seen from Earth |
| solar eclipse | the blocking of sunlight to Earth that occurs when the moon is between the sun and Earth |
| penumbra | the part of a shadow surrounding the darkest part |
| umbra | the darkest part of a shadow |
| lunar eclipse | the blocking of sunlight to the moon that occurs when Earth is directly between the sun and the moon |
| tide | the rise and fall of the level of water in the ocean |
| gravity | the attractive force between two objects |
| satellite | any object that revolves around another object in space |
| geosynchronous orbit | the orbit of a satellite that revolves around Earth at the same rate Earth rotates |
| crater | a round pit on the moon's surface |
| telescope | a device built to study distant objects by making them appear closer |
| maria | dark flat regions on the moon's surface |
| geocentric | the description of the solar system in which all of the planets revolve around Earth |
| heliocentric | a description of the solar system in which all of the planets revolve around the sun |
| inertia | the tendency of a moving object to continue in a straight line or a stationary object to remain in place |
| nuclear fusion | the process by which hydrogen atoms join together to form helium, releasing energy |
| core | the central part of the sun, where nuclear fusion occurs |
| photosphere | the inner layer of the sun's atmosphere |
| 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 produced by the sun's corona |
| sunspot | a dark area of gas on the sun that is cooler than surrounding gases |
| prominence | a loop of gas that protrudes from the sun's surface, linking parts of sunspot regions |
| solar flare | an explosion of hydrogen gas from the sun's surface when loops in sunspot regions suddenly connect |
| comet | a ball of ice and dust in space whose orbit is a long, narrow ellipse |
| asteroid belt | the region of the solar system between the orbits of Mars and Jupiter, where many asteroids are found |
| meteoroid | a chunk of rock and dust in space |
| meteor | a streak of light in the sky produced by the burning of a meteoroid in Earth's atmosphere |
| meteorite | a meteoroid that has hit Earth's surface |
| asteroid | objects revolving around the sun that are too small and too numerous to be considered planets |
| eclipse | the partial or total blocking of one object by another |
Combine with other sets
Share on Facebook
Share on MySpace