What caused some of the bright, diffuse areas of sky in some of the Apollo images from the moon?

Question

There is a large, diffuse, bright area in the otherwise black sky in some of the Apollo mission images from the moon's surface. It is not the sun. What can it be?

In the images below, I am comparing the original image with one I modified by bumping up the contrast and brightness to accentuate the bright areas.

Apollo 14, Feb. 1971. Astronaut Edgar D. Mitchell. What is the big bright area on the right side?

^{Source: AS14-64-9089 (5-6 Feb. 1971) Astronaut Edgar D. Mitchell - High Resolution Picture.}
Left: Original AS24-64-9089. Right: Contrast +60, Brightness +100

Another similar picture, this time from Apollo 11, July 20, 1969, Buzz Aldrin descending the ladder of the Lunar Module (LM). What is the bright area in the upper left, in the sky?

^{Source: AS11-40-5868 (July 20, 1969) ALDRIN DESCENDING LADDER - High Resolution Picture.}
Left: Original AS11-40-5868. Right: Contrast +60, Brightness +100

Same photo (July 20, 1969) from a different source.

^{Source: AS11-40-5868 (July 20, 1969) ALDRIN DESCENDING LADDER - High Resolution Picture.}
Left: Original. Right: Contrast +60, Brightness +100

Got outside at night with a very strong light source such as a 3 million candlepower spotlight just outside the camera's field of view but able to shine on the front surface of the lens from off axis. Overexpose by about 5 stops and you'll get the same thing. There is lens flare in practically every photo. Normally it is muted enough to be made imperceptible by the other light falling on the sensor or film. But when the background is solid black there is nothing to mask the lens flare. — Michael C, Aug 09 '16 at 00:31
I added another picture, AS11-40-5868 (July 20, 1969), which I have from two different sources. One version, once the contrast and brightness is modified, shows a big round light on the black sky, the other not. — Robert Werner, Aug 09 '16 at 05:21
The second photo has clearly been cleaned up before being posted. What question do you still have here? — Philip Kendall, Aug 09 '16 at 08:45
It's also an obviously darker version. Keep pushing the brightness and some of that haze/flare will become more pronounced. — Michael C, Aug 09 '16 at 19:17

score 11 · Answer 1 · edited Apr 13 '17 at 12:44

11

It looks like lens flare. It is an internal reflection inside the lens. It is caused by off axis light allowed to fall on the front surface if the lens from outside the field of view.

For an example of such flare when the exposure is brightened please see: Can you photograph the milky way with a full moon out?

It might also be sunlight reflecting off dust that has been kicked up by the astronaut. In the moon's gravity field that is only 1/6 as strong as that of the Earth's the same amount of force would cause the dust to go 6x higher before falling back to the surface and it would also take 6x as long for such dust to settle as it would in a vacuum under Earth's gravity. There is also no atmosphere and thus no wind to disperse the dust.

It might be possible that dust could be electrostatically stuck to the front of the lens in some of the photos taken on the surface of the moon. In the case of the Apollo 11 photo of Buzz Aldrin descending the ladder of the LEM the absence of such a smudge in photos taken subsequently argues strongly against that theory. The Apollo 11 mission only included a single EVA, so all photos of Aldrin on the Moon's surface were necessarily taken after the photo of him coming down the ladder of the LEM.

This image was 34 frames later from the same film magazine on the same camera as the shot of Buzz descending the ladder:

Notice that there is no evidence of dust on the lens. If one examines all of the images from that magazine it quickly becomes apparent that the angle of the sun to the camera and whether the camera is in the shade of the LEM or not are the most determining factors regarding which images demonstrate the effect and which ones don't.

Likewise, if one examines all of the images in sequence from film magazine LL on the Apollo 14 mission it becomes abundantly clear that lens flare is the main culprit.

edited Apr 13 '17 at 12:44

Community

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answered Aug 08 '16 at 21:11

Michael C

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Or can be a smudge of dust on the front of the lens. But lens flare is the most logical. – Rafael Aug 08 '16 at 22:10
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What could cause such a smudge? The astronaut's hands are inside the gloves of his spacesuit. There would be no way to get skin oil onto the surface of the lens. Skin oil is what normally causes dust to stick to the front of a lens. Also, it takes a LOT of dust to cause a smudge such as that. Remember, they were using medium format Hasselblads on the Apollo Moon landings. – Michael C Aug 08 '16 at 22:17
It could be a bit of both. There's a rumour that the place is pretty dusty. I seem to recall footprints. It wouldn't take much dust to be visible against a vacuum black sky. The general angle appears to be toward the source as well. – Stan Aug 08 '16 at 23:08
It's also rumored to be bone dry, which makes it unlikely that any dust would actually stick to the lens. Or are you saying is might be both lens flare and sunlight reflected on dust suspended in the scene? – Michael C Aug 08 '16 at 23:10
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The dust not necessary stick because of humidity. Probably electrostatic? I do not mean oily smudge, I mean just dust on the lens. Take one filter and put baby powder on it. – Rafael Aug 09 '16 at 00:40
@Rafael Do it in a vacuum with baby powder that has zero moisture in it. I don't think much would stick. – Michael C Aug 09 '16 at 00:45
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@Rafael, & MichaelClark: Then stick it out exposed to the solar wind for 10's of millions to billions of years. "Moondust was a real nuisance for Apollo astronauts," adds Abbas. "It stuck to everything – spacesuits, equipment, instruments." The sharp-edged grains scratched faceplates, clogged joints, blackened surfaces and made dials all but unreadable. "The troublesome clinginess had a lot to do with moondust's electrostatic charge." – Makyen Aug 09 '16 at 06:29
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Yup. I remember have reading about the dust. I have the feeling it should be something like earth's volcanic ash. http://d32ogoqmya1dw8.cloudfront.net/images/NAGTWorkshops/health/case_studies/1354578168.jpg It would be difficult to blow away from the lens :o) – Rafael Aug 09 '16 at 10:59
Attention! A particle of dust, no matter how small it is, settles on the Moon surface as fast as a 1000 kg rock! – Robert Werner Aug 09 '16 at 16:32
@RobertWerner You are correct. But both would only accelerate at only 1/6 the rate they would accelerate on Earth. That is 5.31 ft/sec² rather than 32 ft/sec². When kicked up by an astronaut's boots while travelling upwards they would also only decelerate at 5.31 ft/sec² before falling back to the surface. That also means the same moment of force would make it go 6x higher before falling back to the surface than would be the case (in a vacuum) on earth. – Michael C Aug 09 '16 at 19:14
@Mayken OK, so the dust on the moon is electrostatically charged. That can also be tempered in the case of the Apollo 11 photo that Armstrong and the camera he was using had only been outside the LEM for a very few minutes when he took the shot of Aldrin descending the ladder. In the case of the Apollo 14 photo the camera may have been outside the LEM for much longer at the point the photo was taken. – Michael C Aug 09 '16 at 19:26
Additional evidence against the Apollo 11 photo resulting from dust on the lens would be the absence of such a smudge on many of the other photos Armstrong took on the surface after Aldrin descended the ladder. – Michael C Aug 09 '16 at 19:27
Look at the shadow of the LEM leg brace. Notice that this shot was from within the shadow of the LEM. No light is hitting the lens. The contrast is greater in this shot due to the lack of dust on the lens being illuminated against the sky. Things happen in a vacuum that ground-pounders CAN NOT anticipate. For example: The enamel paint used on the original film canisters had to be discarded because it outgassed a toxic component in a vacuum. – Stan Aug 10 '16 at 02:51
Yeah, but by Apollo 11 they had pretty much worked out all of the kinks with regard to taking photos in a vacuum. They'd been doing it since the first EVAs in the Gemini missions. As to the shadows, it's hard to tell in some of them if the camera was in the shade of the LEM or just on the edge of that shade and in direct sunlight. There was a pretty large gap between the legs and the main body. – Michael C Aug 10 '16 at 05:08
http://www.lpi.usra.edu/resources/apollo/frame/?AS11-40-5858 – Michael C Aug 10 '16 at 05:08
Not to mention that shade protects against conventional veiling and specular lens flare as well as against flare caused by dust on the front surface of the lens. – Michael C Aug 10 '16 at 16:02

score 2 · Answer 2 · edited Nov 14 '16 at 21:56

Thank's to Makyen quote I am posting this option.

It could be some fine dust in the front of the lens.

Fine dust can stick to a surface by electrostatic charges.

Moondust was a real nuisance for Apollo astronauts," adds Abbas. "It stuck to everything – spacesuits, equipment, instruments." The sharp-edged grains scratched faceplates, clogged joints, blackened surfaces and made dials all but unreadable. "The troublesome clinginess had a lot to do with moondust's electrostatic charge."

http://science.nasa.gov/science-news/science-at-nasa/2008/10apr_moondustinthewind/

Now that I think more of it, the pattern does not resemble lens flare, because it is more irregular.

mattdm · Answer 3 · 2016-08-11T19:39:11.877

There are thousands of pictures from the Apollo missions; it stands to reason that many of them exhibit the same sort of defects common to terrestrial photography. In this case, the problem is lens flare, which we can prove to a reasonable degree by comparing the sample images to similar ones where the artifact is more clear.

For example, in AS12-51-7587, from the Apollo 12 Command & Service Modules,

NASA explains:

The brightness in the lower left corner of the photograph is a lens flare caused by sunlight reflecting on the window and the lens of the handheld Hasselblad camera.

See the light purplish pentagon to the right of the moon? That's the shape of the aperture of the lens.

Or, from the lunar surface AS11-40-5873, from Apollo 11,

we again see very obvious lens flare including the pentagonal shape of the aperture. That shape isn't visible in your first example, but that's because it's right on top of the astronaut and thereby obscured. If we look at the next frame in the sequence*, it's more clear, as Mitchell has moved forward:

although it's not exactly perfect geometry, it's definitely apparent as lens flare — and if we look at the same shape with slightly different alignment just a few frames earlier, we see it even more clearly:

Here, the camera is turned so the flare nicely shows a ghost image of the pentagonal aperture, and one can pretty easily see that it's the same general structure as the flare in your first example.

So, overall, there's clear evidence that this is simply lens flare.

To avoid this, the astronauts could have waited until the lunar sky was more overcast, so the sunlight was less harsh. But I guess they were in a hurry. And a lens hood probably would have helped, but it was probably too much of a bother to run back for one.

* Thanks Michael Clark for the link to the gallery.

On the Moon you can not wait for the Sun to change its position on the sky because each day lasts two terrestrial weeks. Apollo 17 had resources for only ~72 hours. Regarding the overcast (https://en.wikipedia.org/wiki/Overcast) it seems that such a phenomenon does not exist on the Moon. — Robert Werner, Aug 11 '16 at 20:26
@Robert Right; it's the camera that has changed position, not the sun. Notice the difference in the background. As for overcast, see the link I provided. I agree that it'd be a long wait. — mattdm, Aug 11 '16 at 20:30

What caused some of the bright, diffuse areas of sky in some of the Apollo images from the moon?

3 Answers3