| A | B |
|---|
| alien | a life form from another planet |
| astrolab | a navigational instrument that measures the elevation of celestial bodies above the horizon in degrees of arc |
| astronomy | the scientific study of objects in outer space |
| axis | an imaginary straight line around which a sphere rotates |
| birth cloud | an area of gas and dust in which stars form |
| focal length | the distance between a lens and the focused image it produces |
| galaxy | a system of billions of stars and their planets; galaxies are either elliptical, spiral, or irregular in shape |
| horizon | the point where the sky meets the Earth from an observer's point of view |
| latitude | distance north or south of the equator, measured in degrees |
| lens | a curved piece of transparent material, usually glass or plastic, that either disperses or concentrates light rays as they pass through it |
| neutron star | a very dense, very small star nearing the end of its life cycle |
| nuclear fusion | the process by which hydrogen atoms inside a star fuse together to form helium, releasing energy that fuels the production of heat and light |
| orbit | the path along which a smaller celestial body revolves around a larger one |
| planet | a celestial body that revolves around a star; unlike a star, it does not produce heat and light |
| power | the measure of a telescope's magnification; the image produced by a 10 power telescope is ten times larger than the object as seen by the naked eye |
| set | to go down below the horizon out of sight |
| solar quadrant | a navigational instrument that measures the elevation of the Sun about the horizon in degrees of arc |
| solar system | Our Sun, the nine planets that revolve around it, and their moons |
| space shuttle | a spacecraft that carries astronauts into space; launched by rocket, it can be flown in orbit and can descend to Earth like an airplane for use again |
| supernova | an exploding star that, though short-lived, gives off vast amounts of energy |
| three-dimensional | having length, width, and depth |
| universe | all of the billions of galaxies and the space in which they exist |
