Orientation of planetary surfaces...

Comments and questions about the APOD on the main view screen.
resuna
Asternaut
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Joined: Thu Jul 29, 2004 1:20 pm

Orientation of planetary surfaces...

Post by resuna » Thu Jul 29, 2004 1:23 pm

Is there something about astronomers and geologists (planetologists?) that makes them expect to see light coming up from beneath when they view a picture? Almost every picture I see of Mars or any other planertary body from orbit seems to be oriented so the illumination is from below, so the craters look like bumps and ridges like ravines. Possibly y'all are so used to it that it doesn't matter... it just pops into perspective for you... or maybe I'm the odd one out who can't make it happen.

I had to save and rotate today's APOD to get an image that made sense.

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RJN
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Post by RJN » Thu Jul 29, 2004 1:50 pm

Hi resuna,
I hadn't noticed this tendancy before, but now that you mention it, many images do appear to be lit from the bottom! On today's APOD, however, if you click on "Melas Chasma" you are taken to a comination image where the B&W part appears to be lit from the top left.
- Robert Nemiroff

resuna
Asternaut
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Joined: Thu Jul 29, 2004 1:20 pm

Synthetic images are different.

Post by resuna » Fri Jul 30, 2004 11:15 am

That's one of those synthetic images where the surface imagery is layered on a topographic map and rendered in a perspective view. They've got a lighting model that's forced on them by the CGI software they're using, and those tend to be relentlessly conventional. I'm talking about the real images from orbiters and probes, the ones selected and arranged by astronomers... it's as if they're expected to be viewed in a dark room with the only light coming from the glowing screen the viewer is crouched over in a fervor of scientific passion, face hilighted from below in a kind of '30s "world of the future" tableau.

dkdowell
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Post by dkdowell » Thu Aug 26, 2004 10:49 pm

I'm sorry I didn't read this topic before starting "Backward Brain?".

I see the reverse image consistently regardless of the direction of illumination. It happens most often when the light is low angle which is preferred because it highlights the relief.

I've never met anyone with the same experience. Is there a name for this phenomenon?