Our Moon and Earth System

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

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)

Birth of Our Moon  “Born” 4-5 billion years ago “Born” 4-5 billion years ago “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

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

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

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

 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 Lunar Features - Maria

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

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

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

 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” phase It’s Just a Phase Phase

FULL QUARTER CRESCENT GIBBOUS FOUR MAIN SHAPES

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

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

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 nutation

 Solar eclipse occurs when the Moon passes directly between the Sun and the Earth and blocks our view of the Sun Solar eclipse Solar eclipse  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 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

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

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

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

Lunar Eclipse  Lunar eclipse occurs when Moon passes through Earth’s shadow Lunar eclipse Lunar eclipse  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

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 lunar eclipselunar eclipse  Gives light a reddish appearance

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

Moon base of the future?  What would you need to live there?