On the Moon, the terminator?

Question

The edge of darkness, and the edge of light?

Let's say you were living at a base on the nearside of the Moon. The line between daylight and darkness would pass your location on a regular basis. About every two weeks, I imagine. I may be wrong but I think that line is called the terminator.

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From your perspective would you be able to see the line of daylight or darkness approaching in the distance?

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How fast would it overtake your position given that the horizon is much closer on the Moon?

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What would you see if you looked up at the Earth. Would the Earth be seen to be eclipse the Sun when darkness begins in your location?

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Would your location be receiving some reflected light from Earth or would your location be in total darkness?

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Whatever happens, I'm sure it would be an awe inspiring sight.

Answer 1

The question about the eclipse is only apropos to a lunar eclipse, not the sunset and sunrise on the moon, which is the subject of the rest of your questions.

Re: Eclipse question: The umbra and penumbra of the eclipse move much more rapidly across the surface than the sunrise/sunset. Let's say an eclipse lasts an hour, meaning roughly that the umbra passes over the surface of the moon in an hour...That would mean that the average speed of the umbra across the moon is the diameter of the moon divided by one hour, or 3500km/h (that's one fast shadow!).

In reference to the sunrise and sunset on the moon:

These events are very slow on the moon, because in the heliocentric frame, the moon is rotating very slowly. You know this because you can look at a full (or anywhere near full) moon when it first rises, and for the following several hours, while it traverses the sky, it looks almost the same.

The speed of the terminator across the moon would be the circumference of the latitudinal circle girding the moon where you were divided by the synodic period (29.5 days). So, if your base were at the equator, the terminator would move (diameter * pi / period) only 370 km/day or 15 km/h. So, you could run (if you brought a good supply of oxygen and you have working legs) to keep up with the shadow. So, it would move at a speed you could see. Yay!

If you were on a base that could see the earth, then yes, you would get some light reflected from the surface and atmosphere and/or refracted from the atmosphere. You can see this "earthshine" from earth looking at a new moon after sunset.

Answer 2

It takes a Moonth, about 28 days, for the lunar day.  So even though the horizon is closer, it moves much slower.  So instead of something like 700 MPH, it's like 25 MPH.  As on the Earth, it's easier to see the shadow move from some elevation.  So put your Moon base on a mountain.

The Moon turns, just like the Earth.  It's not the shadow of the Earth that give you lunar night, it's the shadow of the Moon.  Every now and then, during a lunar eclipse, you'll see the new Earth pass in front of the Sun.  But that's during the day.

During the Lunar night, the Earth goes from 1st quarter, to full, to 3rd quarter.  The Earth is much bigger than the Moon.  And, it reflects more - as the Moon's average reflectivity resembles asphalt. So the Earth is going to really light up your night, and with no pesky clouds in the way. I can read by the light of the Moon.

The latest round of astronaut sign ups had a deadline of July 1st.  Sorry.  But you don't have a relevant science or engineering PhD anyway, right?

Answer 3

Since there is no air on the moon to scatter light, ther terminator (that is the right word) is VERY sharp.    There is no "dusk" or "dawn" on the moon.  Daylight and night time come like !BOOM! and they're there.

Whether or not you could actually SEE the terminator move is another question.  You're right, it takes about two weeks, so the movement would be VERY slow.  

"Solar Eclipses" on the moon would be the same as lunar eclipses seen from earth.  A lunar eclipse is when the moon passes through the earths shadow, so this same event as seen from the moon would become a solar eclipse.  And it would occur at the same time and frequency -- not very often.

Now, the moon orbits the earth in the SAME TIME as it take the moon to rotate -- 28 days.  So the same side of the moon always faces the earth.  Therefore, the earth doesn't "rise" and "set" (as seen from the moon) like the moon does (as seen from the earth) -- one side of the moon always sees the earth, the other side never sees it.

Yes, if you were on the moon "at night" (two weeks) you would get some reflected "earthlight".  This would probably have a slightly blue-ish color.

There ARE pictures taken by the Moon Missions showing the earth as seen from the moon.  Check out www.nasa.gov