Post on 16-Jan-2016
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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