| A | B |
|---|
| astronomical unit | the average distance from Earth to the Sun, approximately 150 million kilometers |
| axis | the imaginary line on which an object rotates (e.g., Earth’s axis runs through Earth between the North Pole and the South Pole) |
| constellation | a star pattern identified and named as a definite group; usually thought of as forming certain shapes or figures in a specific region of the sky |
| galaxy | a large collection of stars, gases, and dust that are part of the universe (e.g., the Milky Way galaxy) bound together by gravitational forces |
| moon | a natural satellite that revolves around a planet |
| moon phase | a phrase that indicates the fraction of the Moon’s disc that is illuminated (as seen from Earth); the eight moon phases (in order): new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter, waning crescent |
| planet | a large body in space that orbits a star and does not produce light of its own |
| solar mass | the quantity equal to the mass of the Sun |
| solar system | a star and all the planets and other bodies that orbit it; the region in space where these bodies move |
| star | a large, gaseous, self-luminous body held together by gravity and powered by thermonuclear reactions |
| Sun | the closest star to Earth and the center of our solar system |
| universe | the total sum of all matter and energy that exists |
