Moon Panorama: shadows, dust, stars? (APOD 10 Dec 2006)

RyGardner · Post by **RyGardner** » Sun Dec 10, 2006 7:28 am

I'm not a skeptic, really, but I do have some curiosity about the shadows in the panarama. I'm assuming the 'compliation' of photographs might have a time lapse, but if you observe the shadow trajectory from left to right, you'll see that there is a significant difference. At left, the shadows are at about 40 degrees off the surface, and almost directly right to left. Then as you pan over, the shadow pivots, is about 40 degrees from left to right where Harrison Schmidt is standing, and is nearly vertical at right. The pattern would be impossible, so far as I could tell, by the natural light from the sun. So, I'm just curious if anyone can shine some light on this for me?

Thanks,
Ry Buffington

Qev · Post by **Qev** » Sun Dec 10, 2006 7:57 am

This is a panoramic image, so across the image, the directions of the shadows are going to seem to change. At the leftmost edge of the image, the Sun is to your right, and shadows will point left. As you scroll to the right along the image, the camera is turning to point directly towards the Sun; the shadows about one-third across the image show this, since they point directly towards the camera. At about two-thirds, the Sun is now to the left of the camera, making the shadows point to the right. And at the far right of the image, the Sun is directly behind the camera, meaning the ground appears brightly illuminated and shadows will point directly away.

Stand in a flat field covered in posts or trees, with the Sun to your right, then slowly do a 360 degree turn clockwise, and you'll observe the shadows of the posts and/or trees doing exactly the same thing.

DomeLiving · Post by **DomeLiving** » Sun Dec 10, 2006 8:32 am

Why is it that most if not all photos from the moon have no stars in the sky?
Also with the famous earth rise you would think that the background should be filled with stars. Is it because it is always daytime on the sunny side of the moon when photos are taken, or some other reason?

craterchains · Post by **craterchains** » Sun Dec 10, 2006 1:55 pm

Most modern photos show the stars, but the older types of photographic methods didnt have the light gathering capacity to get the stars and the brighter imaging of the moon at the same time. If it was set to take pictures of the stars it would show all the moon as white out.

Norval

craterchains · Post by **craterchains** » Sun Dec 10, 2006 1:57 pm

good response QEV

Norval

astro_uk · Post by **astro_uk** » Sun Dec 10, 2006 1:59 pm

Phil Plait has been over this topic in his excellent Bad Astronomy site before the specific link for the answer is http://www.badastronomy.com/bad/tv/foxapollo.html#stars.

In brief the reason you cant see stars is because of the contrast between the very bright objects being imaged (ie the surface of the moon or astronauts) and the very faint stars. The cameras if used on Earth at night wouldnt show any stars either. Try using you camera outside at night with the flash on (to simulate the effect of the bright sun behind you) and take a picture of say a tree in the foreground against the sky, you wont see any stars in the picture.

craterchains · Post by **craterchains** » Sun Dec 10, 2006 2:03 pm

, , , I thought I just said that.

But, I would NOT recomend that site for any real help. FOCLMFAO

Norval

DomeLiving · Post by **DomeLiving** » Sun Dec 10, 2006 3:51 pm

Thank You both for that answer. I should have figured that out for myself but sometimes my brain needs a kick in the pants. I also looked quickly at that "other site" and agree with craterchains. Although 67% of all people asked don’t believe that that site is real either.

astro_uk · Post by **astro_uk** » Sun Dec 10, 2006 4:28 pm

You wouldnt trust badastronomy.com? Just curious why not, its about as rational as you can get.

orin stepanek · Post by **orin stepanek** » Sun Dec 10, 2006 5:19 pm

I like the shadow over to the right; where the antenna and the photographers head got in the picture.
http://antwrp.gsfc.nasa.gov/apod/ap061210.html
Orin

malou · Post by **malou** » Sun Dec 10, 2006 6:16 pm

The shadows STILL don't track to my eye. If ya look over by the antenna part of the shot--the rock shadows are different than the antenna shadows. The antenna's shadow points up and to the left. The rocks right in front of that are pointing down and to the right. How can this possibly be the same light source? The shadows conflict even in the same section of the image.

Even if this is a time lapse...how long did that poor astronaut have to hold still while the image was "captured"?

Qev · Post by **Qev** » Sun Dec 10, 2006 6:54 pm

malou wrote:The shadows STILL don't track to my eye. If ya look over by the antenna part of the shot--the rock shadows are different than the antenna shadows. The antenna's shadow points up and to the left. The rocks right in front of that are pointing down and to the right. How can this possibly be the same light source? The shadows conflict even in the same section of the image.

The shadows there are actually behaving correctly. The rounded shadow of the camera (or astronaut's head) would more-or-less define the point exactly opposite to the Sun, so all shadows to the left and right of that will appear to converge towards a point on the horizon aligned with the head/camera shadow. Ie. shadows on the left will lean right, shadows on the right will lean left.

Even if this is a time lapse...how long did that poor astronaut have to hold still while the image was "captured"?

From the description, I assume it was a series of photographs taken by the astronaut as he turned in place, which were then stitched together to form a single panoramic image. Considering the length of the lunar day, I doubt the shadows changed noticibly between shots.

orin stepanek · Post by **orin stepanek** » Sun Dec 10, 2006 7:11 pm

Besides; if you had more than one light source; you would have overlapping shadows.
Orin

malou · Post by **malou** » Sun Dec 10, 2006 8:18 pm

So, if I stand with my back to the sun, I will have shadows going to the left on right side of my shot and going to the right on the left side of the shot???

no, I still don't buy it.

rigelan · Post by **rigelan** » Mon Dec 11, 2006 12:21 am

Imagine the sun directly behind you, warming your neck. Look at the far right side of the picture. (section 4)

Keep your body the same direction, but look to the left. The shadows are still facing forward. (Section 3)

Turn halfway around, the shadows will face towards you (the middle dark part of the picture, Section 2)

Turn back forward and look to the right, the shadows still face forward (Section 1)

|----1----|----2----|----3----|----4----|

It helps me, and it makes sense to me.

Wadsworth · Post by **Wadsworth** » Mon Dec 11, 2006 12:26 am

Yes the shadows are behaving correctly as Qev said. Try it Malou.

Find a single light source (my ceiling fan) and put two objects on either side of you (i had two water bottles sitting here) and back up keeping the light behind you, the shadows behave just as Qev stated.

RyGardner · Post by **RyGardner** » Mon Dec 11, 2006 1:05 am

Wow, thanks everyone...

I tried the thing with the water bottles, and it works for me too... I get it now. I considered the fact that he was standing still, and turning, and that the shadows would change, but guess I didn't really wrap my head around the way that they would change...

It's pretty wild out there...

Ry

Qev · Post by **Qev** » Mon Dec 11, 2006 8:42 pm

malou wrote:So, if I stand with my back to the sun, I will have shadows going to the left on right side of my shot and going to the right on the left side of the shot???

no, I still don't buy it.

It's actually the exact same effect you get by standing on a railway track (watch out for trains!), and looking along the track. The rails are parallel to each other (one would hope), just like the shadows on the Moon, but as the rails receed into the distance, they appear to converge towards a point on the horizon. It's a trick of perspective.

Another great example of this effect are the anticrepuscular rays we see in the sky here on Earth sometimes, around sunset.

http://www.atoptics.co.uk/atoptics/anti1.htm

All of those 'beams and shadows' are parallel, but they appear to be converging in the distance due to perspective.

Bob41 · Post by **Bob41** » Mon Dec 11, 2006 10:43 pm

I have been looking at the Apollo 17 moon panoramic on Sunday December 10 and it suddenly struck me - why is there no dust ON the many rocks in the picture. There is dust at the base of the rocks but with no air even a meteor impact would not generate a rock clearing event. The meteor would cause a plume of dust that should evenly settle over everything - even the exposed rocks. Now I know that sunlight pushes and the moon shakes but how do you account for the absence of dust on the rocks?

There are many who say the whole Apollo thing was faked but I choose not to believe this - I cry out for man's conquest of space - I am a true and blue Trekkie - but why no dust on the rocks?

I'm At A Loss,

astro_uk · Post by **astro_uk** » Mon Dec 11, 2006 11:00 pm

It looks to me like there is some dust to be seen, in the rocks there are regions that look exactly the same as the surface dust, as if dust has collected in cracks in the rocks.

I think the answer is that the rocks that you can see do not have flat tops, they are pretty much all inclined so even without the effect of quakes which occur periodically I would expect that the dust would simply slide down off the rocks. Especially as the dust is very fine, once one thin layer has filled in the rough parts of the rock, I would guess any additional layers would tend to slide down the sides. Any quakes or impacts would tend to increase the slippage.

I also wonder if the effect of the sun could be important. The difference in temperature between night and day is considerable and could lead to a change in the size of particles, perhaps slight changes in particle size could also make layers of dust unstable to slippage.

Not being a planetary scientist they are my best guesses, I'm sure someone will be along soon to put us straight.

JohnD · Post by **JohnD** » Tue Dec 12, 2006 1:04 am

Bob,
I feel your pain!
But maybe we're just too geocentric, deposition would be quite unlike Earthly windblown detritus.

And look at two places in that pic:
1/ the lumpy rock, aboput four o'clock from the astronaut. There's dust in the depressions and 'lapping' up the sdie nearest the camera that's in sunlight.
2/ the fissured, conical rock, just beyond the cameraman's helmet. There's dust in the cracks.

There's enough atmosphere for winds on Mars, so that you might expect drifts of dust downwind of rocks, but there aren't and some very rough surfaced rocks look very clean there. See: http://marsrovers.jpl.nasa.gov/gallery/ ... 0505a.html

John

JohnD · Post by **JohnD** » Tue Dec 12, 2006 1:15 am

If you are a good enough photographer, you can use flash and see stars in the result! See the work of Wally Pacholka.

Some of his work looks as if it is staged, such as this one, where the mesas appear to cast a flash shadow on the starry background! Obviously a stage set!
http://www.ocastronomers.org/astroimage ... tem\Comets
In fact, the sky moved and so did his camera as it took the long star exposure. The mesa would have shown as a wide, blurred, dark outline. As he finished the exposure with a flash to show the rocks, those only appear in one part of the black, starless outline.

John
PS That link doesn't work unless you add the "\Comets" to the end of it on your browser. Don't know why it wouldn't copy properly. J.

DomeLiving · Post by **DomeLiving** » Tue Dec 12, 2006 6:42 am

astro_uk wrote:You wouldnt trust badastronomy.com? Just curious why not, its about as rational as you can get.

I was just making fun of the statistics found on that page.

DomeLiving · Post by **DomeLiving** » Tue Dec 12, 2006 6:44 am

JohnD wrote:If you are a good enough photographer, you can use flash and see stars in the result! See the work of Wally Pacholka.

Some of his work looks as if it is staged, such as this one, where the mesas appear to cast a flash shadow on the starry background! Obviously a stage set!
http://www.ocastronomers.org/astroimage ... tem\Comets
In fact, the sky moved and so did his camera as it took the long star exposure. The mesa would have shown as a wide, blurred, dark outline. As he finished the exposure with a flash to show the rocks, those only appear in one part of the black, starless outline.

John
PS That link doesn't work unless you add the "\Comets" to the end of it on your browser. Don't know why it wouldn't copy properly. J.

The reason the link didn't work is because the "" needs to be a "/" before Comets.

BTW that is what I expected to see in some of the photos taken on the moon by any of the expeditions going there. I guess though that creative, artistic imagrey is beyond the NASA mind set.

JohnD · Post by **JohnD** » Tue Dec 12, 2006 9:07 am

Thanks, Bruce.
Strangely, while it doesn't work as a link, it does work with the backslash "\" when entered into my browser (IE).

And that is the way the address appeared when I searched for Pacholka's name, went to the Orange County site and found that pic in the album. I just copied the address from there into my post.
Another Wonder Of The InterNet! In the sense, "I wonder why it does that!"

John

Starship Asterisk*

Moon Panorama: shadows, dust, stars? (APOD 10 Dec 2006)

Moon Panorama: shadows, dust, stars? (APOD 10 Dec 2006)

Moon Panorama- where are all the stars?

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