What were the Apollo astronauts able to see when they observed the “dark” side of the moon? I have placed “dark” in quotes because the DSOTM is never 100% dark:
-When the moon is between the sun and the earth, the “dark” side is illuminated by light reflected from earth. In this state, the dark side of the moon is often visible from earth, and so I assume it was also visible to the Apollo astronauts.
-When the earth is between the sun and the moon, the “dark” side is still illuminated by starlight. That’s considerably less light than the previous situation, but was it enough for the Apollo astronauts to see the surface if they dimmed the lights inside the command module?
It’s referred to as the far side of the moon, the side that isn’t facing the earth. When we experience a new moon, the near side is in darkness and the far side is lit as much as the full moon.
You could look up at which phases the moon was moving through during the duration of each mission, but yes, the Apollo astronauts were able to see, and capture images, of the far side lit by the sun.
Incorrect. When the moon is between the sun and the earth, the far side is now lit fully by the sun, and it’s the eternally locked and familiar near side that is lit by earthshine.
This is the new moon phase, and at this time, the moon will rise with the sun and set with it at roughly the same time.
This is the full moon. The far side is now indeed cast in darkness, and starlight may have been enough to shed some light. I believe the orbiter shot flares to illuminate small regions sometimes, but I could be wrong.
Anyhow, the full moon always rises at sunset, and sets at sunrise. The half moon would render the near side and far side both half-lit, and all the phases in between, the far side would be illuminated by the inverse amount of how much the near side is in darkness.
“Dark side of the moon” was a metaphor; it was called “dark” because it could not be seen from Earth, not because it was never lighted. Scientists (hell, high school science students) knew this long before there were space probes: the dark side was lit by the sun at least to some degree except for when there was a full moon.
The Russians had sent unmanned moon probes to photograph the dark side before the Apollo program got off the ground, and that side had been extensively mapped by the time US astronauts saw it.
There were additional constraints on the illumination of the Moon and the timing of the missions. A landing was only attempted when the sun angle at the landing site was between 5 and 14 degrees from the West. The sites span about +/- 30 degrees of longitude from the centre line as seen from the Earth. So as a rough approximation the moon was half full, and there was a “dark” part of the Moon, a quadrant neither lit by the Sun or the Earth. For Apollo 12 this would have been only about 60 degrees wide, but for Apollo 17 about 120 degrees. So, there was a substantial amount of Moon illuminated only by starlight on each mission.
The Moon’s albedo is pretty low - 0.12, despite it’s apparent brightness when full. Starlight has a luminance of about .0003 cd/m[sup]2[/sup]. The human eye can see down to about 10[sup]-6[/sup]cd/m[sup]2[/sup], so indeed yes, a dark adapted eye should be able to see features on the dark side of the moon, and the Apollo missions did overfly a significant amount of moon so illuminated.
No, I understand perfectly; I think my use of the word “dark” here is being misunderstood. Let me retract that, since no portion of the moon’s surface ever experiences zero illumination, and “dark” (depending on you ask) may refer to either the less-illuminated side or to the far side.
So, starting over:
In the situation where the moon is between the sun and the earth, the near side is less illuminated. It still receives some sunlight reflected by the earth (see planetshine); since this is sometimes visible from the earth’s surface, I assume the Apollo astronauts could also see this with their unaided eyes when they were in lunar orbit.
In the situation where the earth is between the sun and the moon, the far side is less illuminated. Unlike the previous situation, it does not receive any sunlight reflected by the earth; the only illumination available is non-solar starlight. My question is whether the Apollo astronauts in lunar orbit could see the surface of the moon under these lighting conditions with their unaided eyes.
Yep, I was aware of that, but my question is not whether anyone has seen the far side of the moon under any circumstances.
Outstanding; thanks for your thorough response. We’re almost there: we now know that it should have been possible for the Apollo astronauts to see portions of the moon illuminated by nothing more than starlight. Did any of the astronauts comment on that aspect of their experience?
But I have heard, if you play the Apollo 11/Houston communications starting at liftoff alongside the Wizard of Oz it’ll be kind of annoying over the duration of the movie.
The six astronauts in the Command Modules orbited the Moon while the other two astronauts were on the surface. So all of them would have seen the far side.
This diagram indicates that the CM orbited the Moon before and after the actual Apollo11 landing. I assume the other missions used similar procedures.
There’s no question that some and probably all Apollo astronauts saw large portions of the Moon never previously directly seen by humans.
I think the OP is asking is if in orbit (or on the surface - I’m not sure) can you see the details on the far side of the Moon during the full moon phase.
On Earth, when there is no moon and the only “natural” light is from stars, I can see the landscape quite well, using only the unaided eye. There’s no reason why the far side of the moon, when not illuminated by the sun or Earth reflection, isn’t subject to the same starlight illumination. It might even be brighter, since there is no atmosphere to attenuate it.
It’s interesting how Machine Elf actually used the terminology correctly in her OP, but everyone assumed that she was using it incorrectly, and thus assumed that she was also making another mistake.