Hello all,

several months ago I came across those Apollo images showing the Earth setting behind the shadowed limb of the moon and spotted this faint glow above the limb. Can anyone verify if this is perhaps the thin lunar atmosphere that can be seen lit up by the earth shine in the otherwise pretty complete blackness of space? If this is unlikely, what else causes it?
I'm referring to the images of Magazine OO, Apollo 17, AS17-151-23174 to 23176, particularly image 23175. If you enhance the contrast on this, you can clearly spot a (red/orange) glow above the moon's limb. You can find the other images here: http://www.lpi.usra.edu/resources/apollo/c...m/magazine/?151

Thank you for any feedback!

This is very unlikely anything other than an image artifact. My guess is something related to film scanning. The fact it's horizontal is very suspicious. It's also connected to bright portions on the film. Below are reduced resolution views of 23173 and 23175, I'll let you draw conclusions.

Click to view attachment

Lunar atmosphere is very thin. I do not believe it could be seen at all in ordinary film or CCD photos. But interference filters loking for the natrium double line or the forbidden lines of the double ionized oxygen should work, if the direct moon light is blocked.

Thanks for clearing this up. I think you are right on. It is also most obvious for the reason there are no hills visible on the "suspected" limb above and below the Earth.

@Harkeppler: Yes, that makes sense. I believe the photo material used in the Hasselblad cameras were very much like Kodakchrome 64, which isn't exactly the ideal stuff for faint lighting.

If there is something there, I would venture it would be more like gegenschein or something along those lines. I can imagine the Earth-Moon system has some dust and gas entrained in it, there may well be a very faint torus of "stuff" that has been sputtered off of the Moon by direct interaction withthe solar wind, and other "stuff" sputtered off of Earth's upper atmosphere by interactions with its own magnetic field. At least some of this stuff would stay in the near area for millions if not billions of years, I would think.

At various angles, the remnant dust and gas in the plane of the ecliptic demonstrates back-scattering effects resulting in fog-like luminsecences. One of those is the famous gegenschein. The dust and gas in the ecliptic and in cislunar space might be visible under the right lighting conditions.

But yes, I severely doubt we're seeing a lunar atmosphere here. After all, keep in mind that each Apollo landing, with the exhaust from the LM descent engine, added more gas to that lunar atmosphere than had been there to begin with, i.e., an increase greater than 100%. Now, spread out the gas from about 18,000 lbs of propellants all around the Moon, and you get an idea of just how thin that stuff has to be...

-the other Doug