| A | B |
|---|
| Electromagnetic spectrum | Arrangement of electromagnetic waves according to their wavelengths |
| Refracting telescope | Optical telescope that uses a double convex lens to bend light and form an image at the focal point |
| Reflecting telescope | Optical telescope that uses a concave mirror to focus light and form an image at the focal point |
| Observatory | Building that can house an optical telescope; often has a dome-shpaed roof that can be opened for viewing |
| Radio telescope | Collects and records radio waves traveling through space; can be used day or night under most weather conditions |
| Rocket | Special engine that can work in space and burns liquid or solid fuel |
| Satellite | Any natural or artificial object that revolves around another object |
| Orbit | Curved path followed by a satellite as it revolves around an object |
| Space probe | Instrument that travels far into the solar system and gathers data that it sends back to Earth |
| Project Mercury | First step in the U.S. program to reach the Moon that orbited a piloted spacecraft around Earth and brought it back safely |
| Project Gemini | Second stage in the U.S. program to reach the Moon in which an astronaut team connected with another spacecraft in orbit |
| Project Apollo | Final stage in the U.S. program to reach the Moon in which Neil Armstrong was the first human to step onto the Moon's surface |
| Space shuttle | Reusable spacecraft that can carry cargo, astronauts, and satellites to and from space |
| Space station | Large facility with living quarters, work and exercise areas, and equipment and support systems for humans to live and work in space and conduct experiments |
