| A | B |
|---|
| Earth's tilt | 23.5 degrees |
| Earth's rotation | Counterclockwise when viewed from the north pole |
| Earth's revolution | 365.25 days |
| Equinox | The two times of the year when days and nights are of equal length |
| Solstice | Either of two times of the year when the sun reaches its highest or lowest point in the sky at noon; marked by either the longest or shortest days of the year. |
| Lunar eclipse | When the Earth is directly between the sun and the moon and the sun's rays are prevented from reaching the moon. |
| Solar eclipse | Occurs when the moon passes between the sun and the Earth and casts a shadow on the Earth. |
| Gravity | The force of attraction between objects due to their masses. |
| Lunar phases | The sequential changes in the appearance of the moon due to its position in the sky and the amount of the sun's light that is reflected. |
| New Moon | Moon phase during with the side that faces Earth cannot be seen because it is not illuminated. |
| Waxing Crescent | This phase occurs after a new moon, less than half of the right side of the moon is illuminated. |
| 1st Quarter | The right half of the moon is illuminated. |
| Waxing Gibbous | More than 1/2 of the right side of the moon is illuminated. |
| Full Moon | Moon phase where the entire side facing the Earth is illuminated. |
| Waning Gibbous | More than 1/2 of the left side is illuminated. |
| 3rd Quarter | The left half of the moon is illuminated. |
| Waning Crescent | Less than 1/2 of the left side of the moon is illuminated. |
| Winter Season | When the tilt of the Earth causes the northern hemisphere to be pointed away from the sun |
| Summer Season | When the tilt of the Earth causes the northern hemisphere to be pointed towards the sun |
| High tide | The bulge of water on the portions of Earth that is caused by the gravity of the moon or inertia. |
| Low tide | No bulge of water on the portions of Earth due to a lack of gravitational influence from the moon. |
| Spring tide | When the gravity of the sun and the moon work together to produce the greatest tidal range. |
| Neap tide | When the gravity of the sun and the moon oppose one another and produce the least tidal range. |
| Umbra | The region of totality during an eclipse |
| Penumbra | The region where a partial eclipse can be seen. |
