55
$\begingroup$

I remember reading several years ago about a mystery or puzzle about a photograph from an Apollo moon landing mission that had to do with why someone's suit was as bright as it was in the photo. There were quantitative questions beyond the normal conspiracy theory-class mysteries.

The reason I remember reading about it is that a new, improved rendering engine that could model complex surfaces and material properties (and substantial computing time) was used to find the answer. While many rendering engines exist that can produce realistically believable images for normal scenes, the result here was essentially photometric rather than just aesthetic.

So far I can't find this result anywhere. I think I read about it 3 to 5 years ago.

Spoiler alert!

The final conclusion was that...

(mouseover the block quote below)

not a fake, we did go to the moon!

$\endgroup$
  • 5
    $\begingroup$ Strictly speaking, the conclusion was that this wasn't necessarily a fake. The new rendering engine does not prove that humanity went to the moon. $\endgroup$ – Lightness Races in Orbit Feb 14 '17 at 14:17
  • $\begingroup$ @LightnessRacesinOrbit Ya, that's correct. It's just that I have been waiting so long to use stackexchange's cool spoiler alert functionality in a technical SE. $\endgroup$ – uhoh Feb 15 '17 at 0:45
90
$\begingroup$

NVIDIA rendered Aldrin descending to the surface and discovered that, just as the conspiracies claimed, it couldn't be reproduced with direct light from the sun as the sole light source. Of course, as in photos on Earth, indirect light (reflected, scattered...) is an important source of scene illumination and must be taken into account.

After adding the indirect, scattered light from the lunar soil and parts of the spacecraft, Aldrin could be seen in the simulation, but still he was darker than in the photograph.

The following are GIF screen captures from the NVIDIA video linked in the article.

enter image description here

However, once NVIDIA included the the highly reflective spacesuit worn by the photographer himself (Armstrong), the simulation matched the photograph.

enter image description here

The key here is the low albedo (reflectivity) of the lunar soil of about 0.12 (12% reflective) compared to the albedo of the white space suit material of about 0.9 (90% reflective). Armstrong's white suit was acting as a reflective "fill light" for Aldrin, who was descending in the shade of the spacecraft.

This is very noticeable from the live video feed - the very bright reflection from Armstrong's suit can bee seen at the left side of the ladder, just below Aldrin's waist.

enter image description here

NVIDIA also added a star field to the simulation with the correct brightness, and demonstrated that stars would be invisible at the short exposures needed for the brightly lit scenes on the moon. When exposures were long enough to show any stars, anything else in the scene would be highly overexposed and completely washed out.

Below is an example of photographers using reflected natural lighting from a highly reflective coated fabric, taken from here:

enter image description here

$\endgroup$
  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – called2voyage Feb 15 '17 at 14:40

protected by ForgeMonkey Feb 14 '17 at 9:25

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).

Would you like to answer one of these unanswered questions instead?

Not the answer you're looking for? Browse other questions tagged or ask your own question.