| A | B |
|---|
| rotation | One complete spin of an object such as Earth on its axis |
| background radiation | Radiation that is left over from the beginning moments of the universe and is coming from all directions in space. |
| revolution | One complete trip orbiting around an object, such as Earth orbiting the Sun |
| crater | A depression in the Moon's surface formed by the impact of objects from space. |
| lunar eclipse | A situation that occurs when the Sun, the Moon, and Earth are in a straight line and Earth's shadow falls across the moon |
| solar eclipse | A blocking of the Sun's light that happens when Earth passes through the Moon's shadow |
| astronomy | The study of the universe |
| tide | The twice-daily rise and fall of the water level along a shore, caused by the gravity of the Moon and Sun |
| gravity | The force of attraction among all objects |
| moon | Any large object that orbits a planet |
| solar system | A star such as the Sun as well as the planets and other bodies that travel around it. |
| inertia | The tendency of a moving object to stay in motion at the same speed and in the same direction |
| meteor | A meteroid that enters Earth's atmosphere and burns with a streak of light |
| meteorite | Any part of a meteroid that reaches Earth's surface |
| parallex | The apparent shift in an object's position when viewed from two locations |
| nebula | A huge cloud of gas and dust in space that is the first stage of star formation |
| black hole | An object whose gravity is so strong that even light cannot escape from it |
| Milky Way | The medium-sized spiral galaxy that is our home galaxy |
| spectrum | A band of colors made when white light is broken up |
| expansion shift | The absorption lines that result in longer (redder) wavelengths from galaxies moving away from each other as space expands |
| big bang | The beginning moment when the universe was very hot and dense resulting in a tremendous explosion |
| Standard Time Zone | A vertical belt, about 15 degrees wide in longitude, in which all places have the same time |
