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Shape distortions of craters due to light effects,

neil phillips

By neil phillips
in Imaging - Lunar

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neil phillips

neil phillips

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Those that know me, have probably seen this around, but i stumbled upon it earlier, and thought it looked interesting, taken fairly closly in time scale, but long enough apart, to show real odd shape effects as the light turns the crater shape first from a pretty circular shape, then to a oval as it comes out of shadow. wonder if theres a name for this effect ?

Neil

2296130074_01bd4b4168_o.png

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ChrisEdu

ChrisEdu

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I expect it's due to the eye not seeing detail in the shadow and so the brain probably 'contracts' the shape, whereas with the lit image the eye is seeing all the detail and thus the brain, when comparing to the shadow image, interpets it as being longer.

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Talitha

Talitha

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No mystery.. it's caused by lunar libration. :hello2:

The Moon 'wobbles' a bit, which allows us to peek over the edge and see what's normally hidden. Features not directly on the limb are seen at a different angles. Sometimes they're more closed, sometimes they're more open.

As an afterthought, I'm adding a composite image made a number of years ago.. notice the placement of the maria in both images. It's easy to see why craters imaged at different times might look very different.

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ChrisEdu

ChrisEdu

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Interesting Neil...

I have had a quick play in CS3 to more closely match the scaling and rotation of the two "images".

10303_normal.png

(click to enlarge)

Billy...

It would be interesting to try superimposing those images to see how well they match up.

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Talitha

Talitha

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As the saying goes Billy, nothing ventured nothing gained...

and learning new things is always a great adventure. :p

Btw, if any of you have downloaded the VMA, go to the 'Ephemeris' tab and manipulate the days backward or forward and you'll see the rolling of the Moon.

Once in a while you may hear of 'favorable libration' for certain features like Mare Orientale. That means the Moon's wobble will favor our view of the WSW limb area, allowing us to glimpse features which are normally over the edge. Libration makes great photo opportunities. :hello2:

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ChrisEdu

ChrisEdu

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No mystery.. it's caused by lunar libration. :hello2:

The Moon 'wobbles' a bit, which allows us to peek over the edge and see what's normally hidden. Features not directly on the limb are seen at a different angles. Sometimes they're more closed, sometimes they're more open.

As an afterthought, I'm adding a composite image made a number of years ago.. notice the placement of the maria in both images. It's easy to see why craters imaged at different times might look very different.

Found this which demonstrates libration nicely. Taken from: http://www.wwu.edu/depts/skywise/lunar_libration.html

post-15252-133877349861_thumb.gif

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ChrisEdu

ChrisEdu

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Aha! Can you post a superimposed version? It would be interesting to know if the effect could be caused purely by the shadow or whether there was a genuine change in the angle of view due to libration. If the size was the same, i.e. the only change was due to illumination then surely libration would not explain the perceived change in shape.

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neil phillips

neil phillips

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Thanks for the interest everyone, and the explanation from Talitha, ( Thats my daughters name too ) Never really thought about it too much untill the other night, when i pulled it off flickr. thanks for processing Billy its all very interesting, can see the shadow superimposed over the highlighted shot,

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