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The Moon
Earth’s Moon
National Optical Astronomy Observatories composite image
The Moon!
• What is the Earth’s natural satellite?
• What does it look like?
• What is its surface like?
• Why does it have phases?
• What are the phases?
What is the Moon?• A natural satellite• One of more than 171 known
moons in our Solar System! There are probably more around the larger planets that have yet to be discovered.
• The only moon of the planet Earth
• The Moon is our moon (see the difference?)
Lunar Origin
• Capture – Once a separate body that was gravitationally captured by Earth. But, requires an interaction of three bodies and is thus very improbable.
• Fission – Moon split off from a very rapidly rotating young Earth. But, such a rapid rotation probably would have broken Earth into many small bodies
• Co-formation – Earth and Moon formed together with their final properties. But, they should resemble each other more closely in the chemical and structural properties
• Impact on Earth of a Mars-sized Planet – Resulted in a fraction of the Earth’s crust and mantle thrown into a region around the Earth. Material then coalesced to form Moon. Best explains lunar properties.
The Moon’s Surface (you should know this)
• No atmosphere• No liquid water• Extreme
temperatures– Daytime = 130C
(265°F)– Nighttime = -190C
(-310 F)
• 1/6 Earth’s gravity
Lunar Features - Highlands
• Mountains up to 7500 m (25,000 ft) tall
• Rilles (trenchlike valleys)
Lunar Features - Craters• Up to 2500 km (1,553 miles) across• Most formed by meteorite impact on the Moon• Some formed by volcanic action inside the Moon
Theory on Crater Formation
• Water drop example
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
Likely interior of the Moon
The meteor broke through
Moon
Earth-facing Side “Far” Side
(From Clementine I - 1994)
Maria
Craters
Can you see the rays?
Does this photo show us a limb or terminator line?
Region of Tychoand Clavius Craters
Photo by H.A. McAlister29 March 1969
Moon (Copernicus Crater Close-Up)
(From Lunar Orbiter 5 - 1991)
93 miles
Moon (Perpetually Shadowed South Pole)
(From Clementine I - 1994)
300 km
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”
Movements of the Moon (you should know all of this)
• 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.
What might this suggest?
One common misconception is One common misconception is that the Moon is only visible at that the Moon is only visible at night. However, the time of night. However, the time of day in which the Moon is in day in which the Moon is in our sky varies depending on our sky varies depending on its phase. This picture clearly its phase. This picture clearly displays the Moon, visible displays the Moon, visible during the day.during the day.
FULL
QUARTER
CRESCENT
GIBBOUS
FOUR MAIN SHAPES
Although the Moon is always lit from the Sun, we see
different amounts of the lit portion from
Earth depending on
where the Moon is
located in its month-long
orbit.
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
Earth
Moon
MoonPlane of earth’s orbit
Plane of lunar orbit
Show BrainPopPhases of the Moon
Show BrainPop Eclipses
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
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!
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
Moon (The Apollo Program)
Six Landings1969 -72
Neil Armstrong’sFootprint
Apollo 11 - 1969
Buzz AldrinApollo 11 - 1969
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
