Science question about an optical illusion type of oddity

[NuclearNed]

This summer I climbed Mt. Rainier. The 2nd day of the climb started at 1 am, so it was pretty dark. Somewhere around 3-4am we could see the sun beginning to rise (i'm assuming we could see it that early because we were at high elevation, ~11,000 feet). We could also see the moon.

The moon looked really strange. It was a normal crescent moon, with only a sliver of the moon illuminated. You could also see the unlit portion of the moon. The strange thing is that the entire moon looked elongated, with a very pronounced oval shape.

Considering how early the climb was, I've always thought that maybe my sleepy brain was playing tricks on my. But I was just now looking at some pictures that one of my co-climbers took, and it seems to match my memory.

What would cause this?

The pic
To see the full effect, you might have to download the full sized version of this pic. Also, the effect seemed much more pronounced when we were seeing it live.

 

[So]

My guess: It's an illusion. It looks like you can see the whole moon, but you really can't see the edges, just a dark blotch. Your mind fills in the rest, making it seem egg shaped but the moon is just lit strangely, making the illumination seem egg-shaped.

 

[NuclearNed]

Originally posted by: So
My guess: It's an illusion. It looks like you can see the whole moon, but you really can't see the edges, just a dark blotch. Your mind fills in the rest, making it seem egg shaped but the moon is just lit strangely, making the illumination seem egg-shaped.

I'm pretty sure it was an illusion But what caused it?

 

[So]

Originally posted by: NuclearNed

Originally posted by: So
My guess: It's an illusion. It looks like you can see the whole moon, but you really can't see the edges, just a dark blotch. Your mind fills in the rest, making it seem egg shaped but the moon is just lit strangely, making the illumination seem egg-shaped.

I'm pretty sure it was an illusion But what caused it?

Well, the sun is of to the left of the picture,and the moon to the right, so I'd say the sun is illuminating the "eastern" face of the moon, which is at an oblique angle to you, making the egg shaped illumination.

 

[lokiju]

Not sure but thats a nice pic!

 

[NuclearNed]

Originally posted by: lokiju
Not sure but thats a nice pic!

Yes it is. I'm not sure how the guy got that pic since it was taken during (in my opinion) the steepest, most difficult, and dangerous part of the climb. In that area I was way too busy trying to not fall off the mountain to worry about taking pictures.

 

[biggestmuff]

Originally posted by: So
My guess: It's an illusion. It looks like you can see the whole moon, but you really can't see the edges, just a dark blotch. Your mind fills in the rest, making it seem egg shaped but the moon is just lit strangely, making the illumination seem egg-shaped.

Thanks, Copernicus.

 

[NuclearNed]

Nobody else has any ideas?

 

[CKent]

Atmospheric distortion? When viewing objects via the horizon you're looking through a lot more atmosphere than when looking straight up.

Btw I'm taking you at your word on the effect; even in the fullsize version the moon is maybe 50 total pixels and I can't see a thing even zoomed in

 

[Kelemvor]

Might be because you were 2 miles up and had less atmosphere to look through so even though that part of the moon wasn't lit directly, you culd still see it in the shadows.

 

[91TTZ]

That's not the Moon- It's a space station!

 

[2Xtreme21]

When I was at the beach 2 weeks ago, a full moon was rising over the horizon and had this same effect. It looked like a giant orange egg until it got maybe 10 degrees above the horizon. My guess is that the atmosphere distorts the moon's image in the same way it distorts the sun's at dusk and dawn.