Our Moon and Earth System

1. Our Moon and Earth System

2. The Moon – Our Nearest Neighbor A natural satellite One of more than 96 moons in our Solar System The only moon of the planet Earth

3. Location, Location, Location! About 384,000 km (240,000 miles) from Earth 3,468 km (2,155 miles) in diameter (about ¼ the size of Earth)

4. Birth of Our Moon • “Born” 4-5 billion years ago • Formed from impact of Mars-sized “planetesimal” on Earth • Moon’s rocks are very similar to those on the Earth

5. Moon’s Interior • 3 major divisions of the Lunar interior • Crust - average thickness of about 70 kilometers • Mantle • Core - radius is between 300 and 425 kilometers

6. The Moon’s Surface • No atmosphere • No liquid water • Extreme temperatures • Daytime = 130C (265°F) • Nighttime = -190C (-310 F) • 1/6 Earth’s gravity

7. Lunar Features - Highlands Rilles • Highlands are the lighter part of the moon • Mountains up to 7500 m (25,000 ft) tall • Rilles (trenchlike valleys)

8. Lunar Features - Maria • Originally thought to be “seas” by early astronomers • Darkest parts of lunar landscape • Filled by lava after crash of huge meteorites on lunar surface 3-4 billion years ago • Mostly basalt rock

9. Lunar Features - Craters • Up to 2500 km (1,553 miles) across • Most formed by meteorite impact on the Moon

10. Movements of the Moon • Revolution – Moon orbits the Earth every 271/3 days • The moon rises in the east and sets in the west • The moon rises and sets 50 minutes later each day • Rotation – Moon turns on its axis every 27 days • Same side of Moon always faces Earth

11. Far Side of the Moon • First seen by Luna 3 Russian space probe in 1959 • Surface features different from near side • More craters • Very few maria • Thicker crust

12. It’s Just a Phase • Moonlight is reflected sunlight • Half the moon’s surface is always reflecting light • From Earth we see different amounts of the Moon’s lit surface • The amount seen is called a “phase”

13. FOUR MAIN SHAPES FULL CRESCENT GIBBOUS QUARTER

15. Tides • Moon affects Earth by the formation of tides • Moon’s gravity pulls on Earth along imaginary line connecting Earth and the Moon that creates bulges of ocean water on both the near and far sides of the Earth • Earth’s rotation contributes to tide formation • As Earth rotates, these bulges align with the Moon • Person at shoreline on Earth’s surface would see ocean level rise every 12 hours

16. Spring and Neap Tides • Sun’s gravitational effect (about ½ of the Moon’s) not as strong as the Moon’s because further away from the Earth • When Sun and Moon are aligned, see stronger tides because effects are combined • These higher tides are called spring tides and they are high when Moon is nearest Earth and Earth is nearest the Sun • Lower than normal tides, or neap tides, occur when the Moon is at a right angle to the Sun-Earth line

17. Nutation • In addition to causing tides, the moon’s orbit around Earth also causes the Earth to nod, or bob throughout its rotational period, called nutation

18. Solar Eclipse • Solar eclipseoccurs when the Moon passes directly between the Sun and the Earth and blocks our view of the Sun • When the Moon perfectly blocks out the Sun’s disk, we only see the dim, gaseous outer layers of the Sun; this is called a total solar eclipse • Partial solar eclipse seen when the Moon blocks a portion of the Sun’s disk

19. Solar Eclipse • The difference between a partial and total solar eclipse can be explained by the fact that the Moon casts a shadow on Earth • Shadow consists of two regions: inner portion called the umbra that doesn’t receive direct sunlight, and an outer portion called the penumbra that receives some sunlight

20. Solar Eclipse • People who witness eclipse from the umbra (inner portion) see a total solar eclipse • People who witness eclipse from the pnumbra (outer portion) see a partial solar ecipse • Umbral shadow very small (~270 km), so total solar eclipse visible from small portion of Earth

21. Effects of Orbits • Only when the Moon intersects the Earth;s ecliptic in line with the Sun and Earth does a solar eclipse occur • Closest point in Moon’s orbit around Earth is called the perigee • Farthest point in Moon’s orbit around the Earth is the apogee

22. Effects of Orbits • When Moon is near apogee, appears smaller from Earth and can’t block out Sun entirely • When Moon is near perigee, appears larger on Earth and can block out Sun entirely

23. Lunar Eclipse • Lunar eclipse occurs when Moon passes through Earth’s shadow • Can only happen during a full moon when the Moon is in the opposite direction from the Sun • Earth has two parts to its shadow like the moon: umbral and penumbral • When entire Moon is in the Earth’s umbral shadow, you can see a total lunar eclipse

24. Lunar Eclipse • Total lunar eclipse lasts approximately 2 hours; can see a Moon during this phase because sunlight that has passed near Earth has been refracted by Earth’s atmosphere • Gives light a reddish appearance

25. Periodicity of Eclipses • Solar and lunar eclipses don’t occur every full moon because the Moon in orbit usually passes above or below the Sun as seen from Earth • Solar and lunar eclipses occur in almost equal numbers, with slightly more lunar eclipses • Maximum number of combined eclipses that can occur per year is seven; this won’t happen again until 2038

26. Moon base of the future? • What would you need to live there?