Our Moon

A look at our nearest neighbor in Space!

The Moon

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What is the Moon?

• 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 the Moon• First Stage • Moon originally was once

part of the Earth.• Scientists believe a very

large body hit the Earth early in its development, throwing a huge amount of debris into orbit.

• Debris eventually was influence by Earth’s gravity and formed the moon we have today.

Second Stage • After forming a sphere, the surface of the moon was covered by molten rock. • Eventually, this mix of rock separated.

Third Stage •The outer surface of the moon cooled, forming a crust. •Craters started to form from the constant bombardment by meteoroids.• Meteoroids decreased• Moon cooled completely• Moon changed little in 3 billion years

Cut to the Core• 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

The Moon’s Surface•Lunar rocks and dust cover most of the surface

• This layer called the regolith

•1 – 6 meters deep

• The lack of an atmosphere let many more meteorites strike the moon’s surface, creating this layer of crushed rock.

•Anorthosites are light-colored, coarse-grained rocks found in the lunar highlands.

•Breccia contains fragments of other rocks that have melted together, and are found everywhere on the moon.

Lunar Features - Highlands

• Mountains up to 7500 m (25,000 ft) tall

• Rilles (trenchlike valleys)

Lunar Features - Craters• Bowl shaped depressions• Up to 2500 km (1,553 miles) across• Most formed by meteorite impact on the Moon• Some formed by volcanic action inside the Moon

Lunar Features - Craters

• When meteorites struck surface they “displaced material”

• Like a “splash”

• Marks left called rays

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

Maria

Craters

Movements of the Moon• Orbit is an ellipse, not circular

• Apogee (farthest from Earth)

• Perigee (closest to Earth)

• Revolution – Moon orbits the Earth every 27 1/3 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

Often Referred to the….

Dark Side of the Moon

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

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”

Waxing and Waning

• New moon

• Waxing Crescent moon

• First Quarter moon

• Waxing Gibbous moon

• Full moon

• Waning Gibbous moon

• Third Quarter moon

• Waning Crescent moon

• New moon

earth

moon orbit`searth

last (third)quarter

gibbous moon

full moon

gibbous moon

first quarter

crescent

new moon

crescent

waning Moon

waxing Moon

SUN

FULL

QUARTER

CRESCENT

GIBBOUS

FOUR MAIN SHAPES

Moon Phases

New Moon – the moon is between the sun and the earth, and we see

the unlighted side. No lighter area of the moon is visible from Earth.

As the sun continues to move, part of the moon becomes visible. When the size of the visible portion is increasing, and we first see a sliver of the moon, it is called the waxing-crescent phase

When the moon has moved through one quarter of its

revolution, the moon looks like a semicircle, called a first-

quarter phase.

The lighted portion of the moon continues to increase, making it larger than a semicircle which is

called the waxing-gibbous phase.

Halfway through its orbit, the Earth is in between the Sun and the Moon, creating a full moon phase. The entire half of the moon is reflecting light off the sun at this phase

The moon continues, now decreasing in the amount of lighten surface. When the moon is not full anymore, but decreasing back to a semicircle, it is called a waning-gibbous phase.The moon continues, now decreasing in the amount of lighten surface. When the moon is not full anymore, but decreasing back to a semicircle, it is called a waning-gibbous phase.The moon continues, now decreasing in the amount of lighten surface. When the moon is not full anymore, but decreasing back to a semicircle, it is called a waning-gibbous phase.The moon continues, now decreasing in the amount of lighten surface. When the moon is not full anymore, but decreasing back to a semicircle, it is called a waning-gibbous phase.

Eventually, the moon reaches a semi-circle again, called the last-quarter phase. The moon continues, now decreasing in the amount of lighten surface. When the moon is not full anymore, but decreasing back to a semicircle, it is called a waning-gibbous phase.

Eventually, the moon reaches a semi-circle again, called the last-quarter phase.

The moon continues, now decreasing in the amount of lighten surface.

When the moon is not full anymore, but decreasing back to a semicircle, it is called a waning-gibbous phase.

Eventually, the moon reaches a semi-circle again, called the last-quarter phase.

The light continues to decrease, when finally only a sliver of the

moon is visible, which is called the waning-crescent phase.

The moon is now back where it started, and the process repeats. The whole process takes 29.5 days (an extra 2 days is needed from the 27.3 days for the moon to get back to its original position) This means that you usually have one of each phase per month. Sometimes, two full moons happen in one month. The second full moon of a month is usually called a blue moon.

Earth

Moon

MoonPlane of earth’s orbit

Plane of lunar orbit

Lunar Eclipses

• Moon moves into Earth’s shadow – this shadow darkens the Moon– Umbra: center, cone

shaped part all the sunlight is blocked

– Penumbra: outer part of the shadow sunlight is only partially blocked.

• About 2-3 per year• Last up to 4 hours

Solar Eclipses• Moon moves between

Earth and Sun• Moon casts a shadow

on part of the Earth• Total eclipses rare –

only once every 360 years from one location!

The Tides

• Tides caused by pull of Moon’s gravity on Earth

• High tide –– Side facing Moon and side away from Moon

– Every 12 hours, 25 ½ minutes

• Low tide –– On sides of Earth

The Calendar

For a long time, people measured the passage of time by keeping track of the phases of the moon.

Eventually, calendars were developed to keep more accurate track of time. The three basic

units of a calendar – day, month, and year – are determined by the movements of the Earth and

moon. A day was defined as the time it takes the Earth to rotate once. A month was defined as the time required for the moon to go through once cycle. A year was defined as the time it

took the Earth to go around the Sun.

Sounds simple, however it was soon discovered that these were not whole

numbers. The Earth takes 365.24 days to go around the sun. A year with 365 days was too short, 366 too long. The moon

makes a complete cycle of phases in 29.5 days. 29 days are therefore too short for a

month, 30 too long. Modern calendars were invented to fix these problems.

Exploring the Moon

• 1950s to 1960s - probes

• Neil Armstrong First man on the Moon – July 20, 1969

• Six Apollo missions (1969-1972)– 382 kg (842 lbs) rocks

• 12 Americans have walked on the moon

When will we return?

Moon base of the future?

• What would you need to live there?