| A | B |
|---|
| Universe | everything in space |
| Astronomer | a scientist who studies the universe |
| Refracting Telescope | a telescope that gathers light with a lens |
| Reflecting Telescope | a telescope that uses mirrors to gather light |
| Observatory | a place where astronomers study the sky |
| Satellite | an object that circles another object in space |
| Space Probe | an unmanned craft sent out into space; space probes do not orbit planets |
| Astronomical Unit | 93,000,000 miles; the average distance between the Earth and the Sun |
| Light Year | the distance light travels in one year |
| Constellation | a group of stars named for an object, person, or animal |
| Galaxy | a group of stars, dust, and gases held together by gravity. |
| Magnitude | a way to measure the brightness of a star |
| Day | the amount of time it takes for a planet to spin once on its axis; on Earth a day is 24 hours |
| Year | the amount of time it takes for a planet to orbit the sun once; on Earth a year is 365 days |
