Chapter 28 Minor Bodies of the Solar System

The Moon

Lunar Facts• Earth’s only natural satellite

• The Moon orbits the Earth at a distance of about 384,000 km (240,000 miles)

• The Moon is about 3,468 km in diameter- about ¼ the size of Earth.

• The Moon orbits the Earth at a 5o angle with respect to the Earth’s orbit around the Sun.

Earth’s orbital plane

Moon’s orbital

plane

Space Exploration

• 1957- the Soviet Union launches, Sputnik, the first artificial satellite

• 1958- the U.S. launched its first, Explorer 1

• Thousands now orbit the Earth

Lunar Missions

• July 20, 1969 Neil Armstrong became the first man on the Moon

• Between 1969 and 1972, the U.S. accomplished six Apollo missions

• 12 Americans have walked on the moon

Apollo 11 MissionFirst Lunar Landing Footage

The Lunar Surface

• No atmosphere• Extreme

temperatures– Daytime =

130C (265°F)– Nighttime = -

190C (-310 F)• 1/6 Earth’s

gravity

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

• Ridges- long, narrow elevations of rock that crisscross the moon’s surface.

Highlands

The Lunar SurfaceHighlands

The Lunar SurfaceMaria

• Dark areas made chiefly of basalt

• Galileo named them for there “sea”-like appearance

• Formed 3-4 billion years ago by magma resulting from massive impacts or radioactive decay

Mare

Lunar FeaturesRilles

Long, deep ancient lava channels leftover from the formation of maria

Lunar FeaturesCraters

•Most formed by meteorite impact on the Moon

•Young craters characterized by bright streaks, called rays

Lunar FeaturesRegolith

Fine layer of dust and rock that covers the moon’s surface

Lunar FeaturesRocks

• Similar to igneous rocks found in Earth’s crust

• Breccia- contain fragments of other rocks fused together

Comparison of the Near and Far Sides

So where did the moon come from?

The Spin or Fission Theory

The Capture Theory

Failed Planet Theory

The Giant Impact Theory

Giant Impact Theory

• Formed 4-5 billion years ago

• Caused by impact of Mars-sized “planetesimal” on Earth

• Debris melted together to form the Moon

Movements of the Moon

• Revolution: the Moon orbits the Earth every 27.3 days

• Rotation – Moon turns on its axis every 27.3 days

• We always see the same side of the Moon because its period of rotation equals its revolution!

• This is called synchronous rotation.

Earth

Moon

MoonPlane of earth’s orbit

Plane of lunar orbit

Orbital Planes of the Earth and Moon

The Earth-Moon System

• Apogee- point at which the Moon is farthest from Earth

• Perigee- point at which the Moon is closest to Earth

Illumination of the Moon• Moonlight is reflected sunlight• Half the moon’s surface is ALWAYS

reflecting light

Illumination of the Moon

• Waxing- occurs when the size of the lighted part of the Moon is increasing

• Waning- occurs when the size of the lighted part of the Moon is decreasing

Phases of the Moon• From Earth we see different amounts of the

Moon’s lit surface• The amount we can see is called a “phase”

starchild.gsfc.nasa.gov/docs/StarChild/questions/phases.html

Phases by Day

Phases

PHASEAPPROXIMATE

DURATION

NEW 1 DAY

WAXING CRESCENT

SEVERAL DAYS

1ST QUARTER 1 DAY

WAXING GIBBOUS

SEVERAL DAYS

FULL 1 DAY

WANING GIBBOUS

SEVERAL DAYS

LAST QUARTER 1 Day

WANING CRESCENT

SEVERAL DAYS

Moon Phases Video

Eclipses• Eclipses are caused when one celestial

body passes through the shadow of another

• The Sun and Moon occasionally line up with the Earth so that an eclipse occurs

• A solar eclipse occurs when the Moon passes between the Earth and the Sun and the shadow of the Moon falls on the Earth

• A lunar eclipse occurs when the Earth passes between the Sun and the Moon and the shadow of the Earth falls on the Moon

Solar Eclipses• When the Moon’s shadow covers part of the

Earth• Only happens at New Moon• Observers in the “umbra” see a total eclipse

(corona is visible)• Those in the “penumbra” see a partial eclipse• Save the date! The next U.S. total solar eclipse

will occur 21 August 2017!

Total Solar Eclipse

• When the Earth’s shadow covers the Moon• A total lunar eclipse occurs when the entire

Moon passes into the Earth’s umbra• A partial lunar eclipse occurs when only part

of the Moon passes into the Earth’s umbra• A penumbral eclipse occurs when the entire

Moon passes into the Earth’s penumbra

Lunar Eclipses

Lunar Eclipses

• Even during a total lunar eclipse, sunlight is bent around Earth through the atmosphere

• The Moon is visible and appears to have a reddish tint

• Save the date! The next U.S. total lunar eclipse will occur 21 December 2010!

The Tides• The Moon’s gravity

tugs on the Earth. – It pulls the most on

the part of Earth closest and least on the farthest causing tidal bulges

• High tide –– Side facing Moon and

side away from Moon

• Low tide –– On sides of Earth

Tidal Patterns

Time for reflection!

Think back to your lunar modeling activity…

Have your preconceptions changed? How?

THE END