2. Tides are an alternate rise and fall in sea level. One effect of the Moon’s gravity is tides. Tides occur because the Moon’s gravity decreases with distance from the Moon. Tides 1 1 Earth’s Place in Space Places on Earth closer to the Moon are pulled harder than places that are farther from the moon.

3. Tides Throughout a day, the water level at the ocean’s edge changes. This rise and fall in sea level is called a tide. Waves 3 3 A tide is a giant wave that can be thousands of kilometers long but only 1 m to 2 m high in the open ocean. The difference between sea level at high tide and low tide is the tidal range.

4. Small differences in the Moon’s gravity cause the water in Earth’s oceans to form two bulges. Tides 1 1 Earth’s Place in Space One bulge is on the side of Earth toward the Moon, and one is on the opposite side.

5. These bulges of water are the high tides. Tides 1 1 Earth’s Place in Space The areas of Earth that are neither toward nor away from the Moon are the low tides.

6. Causes of Tides Tides are created by the gravitational attraction of Earth and the Moon and of Earth and the Sun. Waves 3 3 Gravity pulls harder on particles closer to the Moon than on particles farther from the Moon, causing two bulges of water to form.

7. Causes of Tides Waves 3 3 When the Moon, Earth, and Sun line up together, the high tides are higher and the low tides are lower than normal, creating spring tides.

8. Causes of Tides Waves 3 3 When the Sun, Earth, and Moon form a right angle, high tides are lower and low tides are higher than normal, creating neap tides.

9. Neap Tide Neap tides occur every month when the moon is in the first quarter phase and the last quarter phase.

10. Spring Tides Spring Tides occur every month during the new moon phase and the full moon phase.

11. Eclipses—What causes an eclipse? Eclipses occur when Earth or the Moon temporarily blocks the sunlight from reaching the other. The Moon—Earth’s Satellite 2 2 Sometimes, during a new moon, the Moon’s shadow falls on Earth and causes a solar eclipse. During a full moon, Earth’s shadow can be cast on the Moon, resulting in a lunar eclipse.

12. Eclipses—What causes an eclipse? The Moon—Earth’s Satellite 2 2 An eclipse can occur only when the Sun, the Moon, and Earth are lined up perfectly. Because the Moon’s orbit is not in the same plane as Earth’s orbit around the Sun, lunar eclipses occur only a few times a year.

13. Eclipses of the Sun The Moon—Earth’s Satellite 2 2 A solar eclipse occurs when the Moon moves directly between the Sun and Earth and casts its shadow over part of Earth.

14. Eclipses of the Sun The Moon—Earth’s Satellite 2 2 The darkest portion of the Moon’s shadow is called the umbra. A person standing within the umbra experiences a total solar eclipse. During a total solar eclipse, the only visible portion of the Sun is a pearly white glow around the edge of the eclipsing Moon.

15. Eclipses of the Sun The Moon—Earth’s Satellite 2 2 Surrounding the umbra is a lighter shadow on Earth’s surface called the penumbra. Person’s standing in the penumbra experience a partial solar eclipse. WARNING: Regardless of which eclipse you view, never look directly at the Sun. The light can permanently damage your eyes.

16. Eclipses of the Moon The Moon—Earth’s Satellite 2 2 When Earth’s shadow falls on the Moon, a lunar eclipse occurs. A lunar eclipse begins when the Moon moves into Earth’s penumbra. As the Moon continues to move, it enters Earth’s umbra and you see a curved shadow on the Moon’s surface.

17. Eclipses of the Moon The Moon—Earth’s Satellite 2 2 Upon moving completely into Earth’s umbra, the Moon goes dark, signaling that a total lunar eclipse has occurred. Sometimes sunlight bent through Earth’s atmosphere causes the eclipsed Moon to appear red.

18. Eclipses of the Moon The Moon—Earth’s Satellite 2 2 A partial lunar eclipse occurs when only a portion of the Moon moves into Earth’s umbra. The remainder of the Moon is in Earth’s penumbra and, therefore, receives some direct sunlight. A penumbral lunar eclipse occurs when the Moon is totally within Earth’s penumbra.

19. Eclipses of the Moon The Moon—Earth’s Satellite 2 2 It is difficult to tell when a penumbral lunar eclipse occurs because some sunlight continues to fall on the side of the Moon facing Earth. A total lunar eclipse can be seen by anyone on the nighttime side of Earth where the Moon is not hidden by clouds.

20. Eclipses of the Moon The Moon—Earth’s Satellite 2 2 In contrast, only a lucky few get to witness a total solar eclipse. Only those people in the small region where the Moon’s umbra strikes Earth can witness one.