| A | B |
|---|
| asteroid | a small, solid object that orbits the Sun |
| waning | getting smaller |
| comet | mass of ice, rock, and gas orbiting the Sun |
| constellation | a group of stars in a pattern given a name by people |
| crescent moon | the curved shape of the visible part of the Moon just before and after a new Moon |
| dwarf planet | a round object that orbits the Sun but does not orbit a planet |
| first-quarter moon | a phase of the Moon in the lunar cycle halfway between a new Moon and a full Moon |
| force | a push or pull that can change the speed and direction of a moving object |
| full moon | the phase of the Moon when all of the sunlit side of the Moon is visible from Earth |
| gas giant planet | one of the four planets that are made of gas. These are Jupiter, Saturn, Uranus, and Neptune. |
| gibbous moon | he shape of the Moon when it appears to be more than a quarter but not yet full and when it is less than full but not quite a third quarter. |
| gravity | the force that holds the Earth in the orbit around the sun |
| lunar cycle | the 4-week period during which the Moon orbits Earth one time and goes through all of its phases |
| Moon | Earth’s natural satellite |
| night sky | the time when the sky is dark and certain astronomical objects can be observed, such as the Moon, stars, and planets |
| new moon | he phase of the Moon when the sunlit side of the Moon is not visible from Earth |
| phase | the shape of the visible part of the Moon |
| planet | a large, round object orbiting a star |
| solar system | he Sun and the eight planets and other objects that orbit the Sun |
| star | a huge sphere of hydrogen and helium gas that radiates heat and light |
| terrestrial planet | one of the four small, rocky planets closest to the Sun. These are Mercury, Venus, Earth, and Mars. |
| third-quarter moon | a phase of the Moon in the lunar cycle halfway between the full Moon and the new Moon |
| waxing | getting larger |
| asteroid belt | a band of orbiting rubble that separates the gas giant planets from the terrestrial planets |
