| A | B |
|---|
| Sphere | Round, 3-d object, the surface of which is the same distance from the center in all directions |
| Gravity | The attractive force between two objects that depends on the masses of the objects and the distance between them |
| Magnetic Field | Protects the Earth from harmful radiation from the Sun |
| Van Allen Belts | Belts of charged particles trapped from solar wind |
| Time Zone | An area 15 degrees wide in which the time is the same |
| Rotation | The spinning of Earth on its axis, takes 24 hours |
| Earth's Axis | An imaginary line from Earth's rotational north pole to its rotational south pole |
| Revolution | The motion of Earth in its orbit around the Sun; takes 365 days |
| Reasons for seasonal changes | Earth's rotation, Earth's revolution, the tilt of Earth's axis |
| Equinox | When the Sun is directly over the Earth's equator and the number of daylight hours equals the number of nighttime hours all over the world |
| Solstice | When the Sun reaches its greatest distance north or south of the equator |
| Winter Solstice | December 21 in northern hemisphere |
| Summer Solstice | June 21 in northern hemisphere |
| Spring Equinox | March 21 in northern hemisphere |
| Fall Equinox | September 21 in northern hemisphere |
| Tide | The rise and fall in sea level, caused by a giant wave produced by the gravitational pulls of the Sun and the Moon |
| Spring Tide | Tide where the Moon and the Sun pull together (lined up) |
| Neap Tide | Tide where the Moon and Sun are at right angles |
| Moon Phases | The changing appearances of the Moon as seen from Earth |
| New Moon | Occurs when the Moon is between the Earth and the Sun - moon cannot be seen |
| Waxing Phases | After a new moon, when the lighted portion that we see appears larger each night |
| First Quarter Moon | After a new moon, when we see one-half of the Moon's lighted side |
| Full Moon | Occurs when we see all of the Moon's lighted side because the Moon is on the side of Earth opposite from the Sun |
| Waning Phases | After a full moon, when the lighted portion that we see begins to appear smaller |
| Third Quarter Moon | After a full moon, only half of the side of the Moon facing Earth is lighted |
| Eclipse | Occus when the Earth or the Moon temporarily blocks sunlight from reaching the other object |
| Solar Eclipse | Occurs when the Moon moves directly between the Sun and the Earth and casts a shadow on part of Earth |
| Lunar Eclipse | Occurs when Earth's shadow falls on the Moon |
| Crater | Depression formed on the Moon from meteorites, asteroids, and comets |
| Maria | Dark-colored, relatively flat regions on the Moon's surface |
| Regolith | Debris from impacts on the Moon |
| Moon's Interior from inside out | Core, Lower Mantle, Upper Mantle, Crust |
| Giant Impact Theory | The Moon formed 4.6 billion years ago when a Mars-sized object collided with Earth and gas and other debris condensed into a large mass |
