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I realise that night time on the Moon is two weeks, however I am curious if during the night there, whether or not the Earth reflects light in similar manner to the Moon.

On the one hand, I know it must (as seen in photographs from astronauts), but what I'm really wanting to know is:

Does the Earth have phases like the Moon and do they work in a similar manner for an observer on the Moon?

I assume the Earth isn't as reflective as the Moon since the Moon is much lighter in colour, however the Earth is also fairly larger, does this make any difference in the amount of light reflected?

Finally, if the Earth does appear in phases, does that mean that the two week long nights on the Moon are sometimes pitch black (new Earth) and sometimes less than pitch black (full Earth)?

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From the perspective of the Moon, the Earth exhibits phases just as does the Moon when viewed from the perspective of the Earth. There are however some differences. One difference is that the phase of the Earth at a fixed local lunar time will be pretty much the same from one day to the next. This is a result of the fact that the Moon is tidally locked. Another difference is that earthlight is considerably brighter than moonlight. This is a consequence of the Earth's significantly larger albedo and significantly larger diameter compared to the Moon. A third difference is that except for locations close to ±90° lunar longitude, the Earth doesn't rise and set.


I assume the Earth isn't as reflective as the Moon since the Moon is much lighter in colour, however the Earth is also fairly larger, does this make any difference in the amount of light reflected?

You have this backwards. The Moon is rather dark. It's reflectivity is about that of old asphalt. The Earth is significantly more reflective than is the Moon.

Finally, if the Earth does appear in phases, does that mean that the two week long nights on the Moon are sometimes pitch black (new Earth) and sometimes less than pitch black (full Earth)?

No. This is the first difference between Moon phases and Earth phases. Earth phase on the Moon is a function of lunar longitude and time of lunar day. You won't see a full Earth one night and a new Earth some other night.

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  • $\begingroup$ Nice answer. I get the feeling a full earth, viewed from the moon would be quite spectacular. $\endgroup$ – userLTK Jul 24 '15 at 20:42
  • $\begingroup$ One convenience available from the moon but not from Earth, is that you can tell time by seeing where the terminator lies on the Earth. It would take a little practice, and it wouldn't be available twice a month, but if you're a long time resident on the moon, you could tell time at a glance. $\endgroup$ – Howard Miller May 1 '16 at 22:05
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The moon only seems light in color against the backdrop of the void. It's actually fairly dark. Moon's albedo (scientific term for how reflective something is) is .12 and Earth's .3. So earth is two and a half times more reflective. Moreover the moon subtends about half a degree as seen from earth while the earth subtends nearly two degrees as seen from the moon. A full earth is about 34 times as bright as a full moon.

From the point of view of someone on the moon, the earth seems to stay in one part of the sky. This is because the moon is tidelocked to the earth. That is it always presents the same face to us. But since the moon's orbit isn't perfectly circular and it's equator is tilted with regard to it's orbital plane, the earth moves a little.

Let's say we're standing in the lunar crater Mösting A. This is the region of the moon closest to the earth. From this vantage point the earth is always straight up. At high noon the sun seems to be near the earth and we see either a thin crescent earth or a new earth. At midnight the sun's moved 180º and we're seeing a bright, full earth. So in this location earth is brightest at midnight and darkest at noon. This area always enjoys either earthlight and/or sunlight except doing an eclipse

If we're standing in a region near what we see as the edge of the moon, the earth is low in the sky near the horizon. Again, the earth is a thin crescent or a new earth when the sun is close to the earth in the sky. So there can be a new earth near the horizon while the sun is still behind the horizon (i.e. just before sunrise or just after sunset). In this case you'd have neither earthlight nor sunlight.

Most of the near side enjoys earthlight all or nearly all of the night.

On the far side of the moon, you never see the earth. The nights are always dark.

So the Pink Floyd lyrics make some sense after all.

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Yes, there are Earth phases, viewing from the Moon. Full earths, half earths, quarter earths, waning and waxing earths. The easiest way to visualize this is, imagine the earth is still, one half of the Earth facing the sun, the other half away from the sun, so you have half the Earth is light, half is dark, now, imagine you're on the moon orbiting the Earth every 28 days. When you're over the sunny half of the Earth (night on your part of the Moon) the Earth is full. When you're over the dark side of the Earth (day on your part of the Moon), the Earth is new. As the moon takes 28 days to orbit the earth, like the moon in our sky, every 28 days would complete one cycle.

What's different is the Earth wouldn't move in the night sky. It would actually go back and forth a bit, but it would stay in the same general area, every day, every year, every century, because the Moon is tidally locked to the Earth, but apart from not moving, it would be similar to the Lunar cycles.

Another difference is that you could observe the Earth's rotation. Here's a pretty good video on what it would look like. 28 days squeezed into about 1 minute.

https://www.youtube.com/watch?v=-HgHEO0DUig

I would imagine the Earth looks quite bright from the point of view of the Moon, and I'd guess the pictures don't really do it justice, but that's just a guess. I've never seen it for myself. I'm also not sure it would be pitch black and not visible as a "New Earth" either. I remember reading that you can see stars from the moon even during the day, that's because there's no atmosphere to diffract the light so you could probably see the Earth even at new earth too. We can see the new moon from Earth sometimes, so I would think a "new earth" would be visible but dark.

Here's a discussion on being able to see the new moon. I would think, seeing a new earth from the moon would be even easier.

Short discussion: http://scienceline.ucsb.edu/getkey.php?key=26

Long discussion: https://physics.stackexchange.com/questions/1907/why-can-we-see-the-new-moon-at-night

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