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?

• 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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http://www.youtube.com/watch?v=sNUNB6CMnE8&feature=player_embedded

http://www.classzone.com/books/earth_science/terc/content/

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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• 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• 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:• 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

• 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?

• 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.