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)

Movements of the Moon

• 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

The Tidally Locked Orbit of the moon

The moon is rotating with the

same period around its axis as it is orbiting Earth

(tidally locked).

We always see the same side of the moon facing Earth.

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”

• NO “DARK SIDE!!”

Terminology

a. Limb – Circular edge of the moon. May be dark or illuminated

b. Terminator – boundary between the illuminated disk and the dark part of the moon

c. Waxing – growing

d. Waning – shrinking

FULL

QUARTER

CRESCENT

GIBBOUS

FOUR MAIN SHAPES

The Phases of the Moon (I)

As the moon orbits around Earth, we see different portions of

the moon’s surface lit by the sun, causing the phases of the

moon.

The Phases of the moon (II)New moon First Quarter Full moon

Evening Sky

The Phases of the moon (III)Full moon Third Quarter New moon

Morning Sky

The Orbit of the moon (I)• The moon orbits Earth in a sidereal period of 27.32 days.

27.32 days

Earthmoon

Fixed direction in space

The Orbit of the moon (II)

• The moon’s synodic period (to reach the

same position relative to the sun) is 29.53 days (~ 1 month).

Fixed direction in space

Earth

moon

Earth orbits around sun => Direction toward sun changes!

29.53 days

Lunar Eclipses

• Moon moves into Earth’s shadow – this shadow darkens the Moon– Umbra– Penumbra

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

Lunar EclipsesEarth’s shadow

consists of a zone of full shadow, the

umbra, and a zone of partial shadow, the penumbra.

If the moon passes through Earth’s full

shadow (umbra), we see a lunar eclipse.

If the entire surface of the moon enters the umbra, the lunar

eclipse is total.

A Total Lunar Eclipse (I)

A Total Lunar Eclipse (II)

A total lunar eclipse can last up to 1 hour and

40 min.

During a total eclipse, the moon

has a faint, red glow, reflecting

sunlight scattered in

Earth’s atmosphere.

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!

Solar Eclipses (I)

The angular diameter of the moon (~ 0.5o) is almost exactly the same as that of the sun.

This is a pure chance coincidence. The moon’s linear diameter is much smaller than that of the sun.

Solar Eclipses

Due to the equal angular diameters, the moon can cover the sun completely when it passes in front of the sun,

causing a total solar eclipse.

Total Solar Eclipse

Prominences

Chromosphere and Corona

Diamond Ring Effect

Earth’s and moon’s orbits are slightly elliptical:

sun

Earth

moon

(Eccentricities greatly exaggerated!)

Perihelion = position closest to the sun

Aphelion = position furthest

away from the sun

Perigee = position closest to Earth

Apogee = position furthest away from

Earth

Annular Solar EclipsesThe angular sizes of the

moon and the sun vary,

depending on their distance from Earth.

When Earth is near perihelion, and the moon is

near apogee, we see an annular solar eclipse.

Perigee Apogee Perihelion Aphelion

Almost total, annular eclipse of May 30, 1984

Approximately 1 total solar eclipse per year

Conditions for Eclipses (I)

The moon’s orbit is inclined against the ecliptic by ~ 5º.

A solar eclipse can only occur if the moon passes a node near new moon.

A lunar eclipse can only occur if the moon passes a node near full moon.

Partial Eclipse

Earth

Moon

MoonPlane of earth’s orbit

Plane of lunar orbit

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

Name this phase!

Full MoonWhat time does this phase rise and set?

Name these features.

Name these

features.

Craters

Maria

Does this image show us the near side or far side of the moon?

Far SideHow can you tell?

Is this line the limb or terminator?

Is this line the limb or terminator?

Limb

Terminator

Name this phase!

First Quarter

Name this phase!

Waxing Crescent

Does this image show the near side or the far side of the moon?

Near Side

Name this phase!

Waning Gibbous

Name this phase!

Third Quarter

From what direction does the moon rise?

The East

Name this phase!

Waxing Gibbous

Name this phase!

Waning Crescent

What might be happening in this image?

Lunar Eclipse

Is this line the limb or the terminator?

Limb

Name this phase!

Look closely!

Waxing Gibbous

True or False:

The Far Side and the Dark Side of the moon

are the same thing.

False!

Name this phase!

Full Moon

Name this phase!

New Moon

Does the moon rise or set in the west?

It sets in the west.

Name this phase!

Waning Gibbous

Name this phase!

Waning Crescent

Name this phase!

Waning Gibbous

The Lunatic: Leesa Hubbard

Photo resources• http://www.nasm.si.edu/apollo/AS15/a15images.h

tm• http://nssdc.gsfc.nasa.gov/photo_gallery/photogall

ery-moon.html#apollo• http://clementine.cnes.fr/index.en.html• http://cass.jsc.nasa.gov/pub/research/clemen/clem

en.html• http://spaceflightnow.com/news/n0108/15mooncre

ate/• http://seds.lpl.arizona.edu/nineplanets/nineplanets/

pxmoon.html

More photo resources

• http://www.nrl.navy.mil/clementine/clemovies/clemovies_index.html

• http://www.solarviews.com/eng/moon.htm• http://news.bbc.co.uk/1/hi/sci/tech/620649.stm• http://skyandtelescope.com/observing/objects/ecli

pses/article_99_1.asp• http://lunar.arc.nasa.gov/results/ice/eureka.htm• http://www.space.com/scienceastronomy/solarsyst

em/moon_nss_020604.html

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