| A | B |
|---|
| Telescope | A device built to observe distant objects by making them appear closer |
| Visible light | Electromagnetic radiation that can be seen with the unaided eye |
| Wavelength | The distance between the crest of one wave and the crest of the next wave |
| Observatory | A building that contains one or more telescopes |
| Constellation | An imaginary pattern of stars in the sky |
| Apparent brightness | The brightness of a star as seen from Earth, how bright it looks |
| Absolute brightness | The brightness of a star if it were at a standard distance from Earth, how bright it is |
| Light-year | The distance that light travels in a year |
| Nebula | A large cloud of gas and dust in space, spread out in immense volume |
| Protostar | A contracting cloud of gas and dust that produces radio waves |
| Pulsar | A rapidly spinning neutron star that produces radio waves |
| Black hole | An object whose gravity is so strong, nothing escapes, not even light |
| Binary star | A star system with two stars |
| Open cluster | A star cluster that has a loose, disorganized appearance and contains no more than a few thousand stars |
| Globular cluster | A large, round, densely-packed grouping of millions of older stars |
| Galaxy | A huge group of single stars, star systems, star clusters, dust, and gas bound together by gravity |
| Quasar | An enormously bright, distant galaxy with a giant black hole at its center |
| Universe | All of space and everything in it |
| Scientific Notation | A way to write very large or very small numbers in shorter form |
| big bang | The initial explosion that resulted in the formation and expansion of the universe |
| Hubble's law | The observation that the farther away a galaxy is, the faster it is moving away |
| Cosmic background radiation | The electromagnetic radiation left over by the Big Bang |
| Planetesimal | A small asteroid-like body that formed the building blocks of planets |
| Dark matter | Matter that does not give off electromagnetic radiation but appears to be quite abundant in the universe |
| Elliptical galaxy | A galaxy shaped like a round or flattened ball |
