Goal: To understand the
moon as we view it.
Objectives:
1) To learn about the Phases of the moon.
2) To understand the size of the moon, and its
relation to earth
3) To see the surface of the moon.
4) To know the make up of the moon.
5) To learn about the formation of the moon.
6) To understand what it will take to colonize the
moon.
7) To discover some Fun Moon notes and myths.
Phases of
the moon
Every 29.5 days the moon goes
through a cycle that you see on
the right.
There are 8 phases.
Phase 0/8 – new moon (bottom right)
Phase 1 – waxing crescent (top row)
waxing = light is growing
Phase 2 – first quarter (far left of 2nd row)
Phase 3 – waxing gibbous – 3rd row
Phase 4 – full moon – first of row 4
Phase 5 – waning gibbous (rest of row 4)
waning = light is shrinking
Phase 6 – 3rd quarter (2nd + 3rd of row 5)
Phase 7 – waning crescent (first 3 of
bottom row)
How many days of sunlight per
lunar month does the far side of the
moon (sometimes called the “dark
side”) get?
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A) 0 days
B) ~ 1 day
C) ~ 7.4 days
D) ~ 14.7 days
E) ~ 3.7 days
How many days of sunlight per
lunar month does the far side of the
moon (sometimes called the “dark
side”) get?
• D) ~ 14.7 days – same as the near side
• The far side gets just as much sunlight as the
near side.
• We just never see the far side because it is
“tidally” locked to the earth (i.e. the rotational
period is equal to the orbital period).
• Therefore we only see one of the sides of the
moon.
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• We shall now examine why the phases are
created.
• They are a combination of the moons orbit
around the earth with the fact that only the
side facing the sun is lit.
Elongation of the moon
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The elongation of the moon is the angle made by the sun to the earth to the moon.
Each phase is based on the elongation, and lasts for 45 degrees.
So, the new moon (Phase # 0 or 8) starts at 0 degrees, and ends at 45 degrees.
The Waxing Crescent (phase #1) would start at 45 degrees and end at 90
degrees.
Phases vs rise and set times of the
moon
• Therefore, each phases will rise and set at
a different time of day.
• If you remember back to the beginning of
the semester when we looked at the
motions of stars we learned that the earth
rotates 15 degrees per hour.
• Therefore for every 15 degrees that the sun
leads ahead of the moon, it will take 1 hour
for the earth to rotate from when the sun
rises to when the moon will rise after it.
If the moon has an elongation of
150 degrees (waxing gibbous), and
the sun rises at 6 AM, about what
time will the moon rise?
HINT: earth rotates 15 degrees per
hour
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A) 6 AM
B) 11 AM
C) 4 PM
D) 6 PM
E) 11 PM
If the moon has an elongation of
150 degrees (waxing gibbous), and
the sun rises at 6 AM, about what
time will the moon rise?
• C) 4 PM
• Which is 150/15 = 10 hours after the sun
rises. 6 AM + 10 hours = 4 PM
• What time will the moon set (hint, how
many hours per day is the sun up?)?
If the moon has an elongation of
150 degrees (waxing gibbous), and
the sun rises at 6 AM, about what
time will the moon rise?
• C) 4 PM
• Which is 150/15 = 10 hours after the sun rises.
• What time will the moon set?
• 4 AM – 12 hours later.
• (also good to note that every night the moon
rises and sets about 50 minutes later)
Size of moon, relation to earth:
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Question 1:
Suppose the earth was a basketball 1 foot in diameter.
What would the size of the moon be?
A) 1 foot
B) 2 feet
C) 0.5 feet
D) 0.25 feet
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Question 2:
How far from the earth would the moon be in this new scale?
A) < 1 foot
B) 1-9 feet
C) 10-90 feet
D) > 100 feet
Size of moon, relation to earth:
• Question 1:
• Suppose the earth was a basketball 1 foot
in diameter.
• The earth is 8000 miles in diameter. The
moon is 2000 miles in diameter.
• Therefore the moon would be 3 inches in
diameter. This is roughly the size of a fist
or a baseball.
Size of moon, relation to earth:
• What would the size of the moon be?
• Question 2:
• How far from the earth would the moon be
in this new scale?
• The moon is 250,000 miles from the earth
on average, which is just over 30 earth
diameters.
• Therefore, the moon would be a baseball
30 feet away from the basketball sized
earth.
Surface of the moon
• What features are on the surface of the
moon?
• Dark areas = lunar mare (seas)
• Light areas are the Lunar Highlands.
• The moon is dotted by numerous caters.
Make up of the moon:
Outer part (grey)
= crust
Red = mantel
Orange = possible
transition zone
Yellow = core
Lunar quirks:
• 1) small core
• 2) most of the moon is made of similar material
as the earth
• 3) the moon is lacking in iron
• 4) the moon’s orbit is not along either the earth’s
equator like most orbits are, and it is not along
the ecliptic. It is offset from the ecliptic by about
5 degrees.
• 5) The moon is getting 3 cm further from the
earth every year
How was the moon formed?
How was the moon formed?
• The moon most likely formed after a Mars sized object
collided with the earth during the formation of the solar
system.
• The collision produced a debris field.
• This debris field would be largely material thrown up
from the mantel of the earth.
• The moon would have started to form on the edge of the
debris field.
• Material in the field would be pushed out tidally (which
we will discuss tomorrow) and accreted by the newly
forming moon.
• This process would take < 1000 years to complete.
What does that mean for the
surface of the moon?
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The highlands
are the oldest
part of the
surface and are
4.5 billion years
old.
They are very
heavily cratered
Craters within
craters even.
Photo of the far
side of the moon
by Apollo 11.
Largest crater
here is 30 km
wide.
Mare vs highlands
• Notice the mare have a
few craters, but not nearly
as many as the highlands.
• Meanwhile the highlands
are covered with them.
• The mare are only 4.0
billion years old.
• The early solar system
was known as the era of
heavy bombardment –
where debris was
everywhere, so impacts
occurred in great numbers.
• By the time the mare
formed, the bombardment
had ended.
Surface of the moon:
• Why are there
so many
craters down
to such small
sizes, and why
do they
remain today?
No water or atmosphere!
• No water means no erosion. So, craters
stay until covered up by landslides or
future craters.
• No atmosphere (or at best a few particles
of one) means single atoms can hit the
moon. Therefore there are craters even
down to the microscopic level.
• These are challenges we will be faced with
if we ever colonize the moon.
Colonizing the moon: another challenge
Moonquakes!
• Occur very often.
• Probably the results of landslides.
• Might also be a slow effect of the moon
returning to shape after a possible asteroid
impact a few thousand years ago.
• We would have to build buildings which
can withstand them.
Biggest challenges:
• Getting back there!
• It is EXPENSIVE to land humans on the
moon.
• More expensive to send enough supply for
a colony.
• Have to eat and drink!
• Oops, we don’t have a rocket to do it
anymore! Plans all gone, scientists no
longer in the land of the living 
Moon myths and asides!
• Myth one: The moon looks much bigger
on the horizon.
• This one is false. It is an optical illusion.
The moon only seems that way. If you
hold a thumb out to it, it will be the same
size. However, on the horizon, we see it is
far away, so our brain thinks it must be
huge. In the sky, there is no references
for our brain to fool us.
Moon myths and asides!
• Blue moon:
• 2 full moons in the same month.
• Also, each month’s full moon has its own
name. September’s is the harvest moon
for example.
Moon up?
• A common myth is that the moon is always up at
night, and only at night.
• As we have found today, the rise and set times
of the moon change by 50 minutes per day. So,
sometimes the moon is actually up in the DAY
and not night (although the crescent moons
aren’t really observable while the sun is up
because the sun glares them out, but quarter
phases can been seen ).
Big Moon
• There is a myth that the moon appears
really big when it is close to the horizon.
• This is an optical illusion, however.
• Do this as a test, hold your thumb out as
far out as you can.
• Near the horizon it will be about a third to
a quarter of the size of your thumb.
• When it is high in the sky it will be the
same size.
Earth viewed from the moon!
• The earth would have phases also.
• However, since the moon rotates at the same rate it
orbits, the earth would stay centered on 1 spot in the
sky.
• Even at night,
you would see the
earth (in fact, you
would have a full
earth during the
night, and new
earth during the day
Conclusion
• Moon has phases which are determined
by the moon’s position in its orbit around
the earth.
• The moon has some interesting surface
conditions.
• The moon formed due to a Mars sized
object colliding with the earth.
• There will be many challenges when
colonizing the moon.