Our Moon and Earth System

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 y

ears 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 = 130C

(265°F)• Nighttime = -190C

(-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”

It’s Just a 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

Solar eclipse occurs 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

Solar Eclipse

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

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

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?