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Schickard, Phocylides, and Nasmyth

dob moon observing report
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#1 FRANC LILL

FRANC LILL

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Posted 14 October 2019 - 05:39 AM

Hi all,

 

 

Note the shadow projected by a summit on the N edge of Phocylides that stretches across the plain over a distance of 70 km! This summit must be particularly high. A quick calculation determines an altitude of 4000m! but only 4 summits on the visible side that have a height exceeding 4 km are listed .....? In fact that summit is located on the edge of the crater Nasmyth at the place where it was countered by the edge of the crater Phocylides.

Thank you for comments...

 

Clear sky,
Francis

 

 

Cell phone picture from sept. 11th, 2019 at 21:34 UT afocal mount with 9mm Nagler eyepiece behind a 16" dobsonian.

 

 

190911-23h34-Schikard-PhocylidesA.jpg


Edited by FRANC LILL, 14 October 2019 - 05:40 AM.

  • frank5817, John_Moore, happylimpet and 2 others like this

#2 Larrythebrewer

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Posted 14 October 2019 - 11:04 AM

“In fact that summit is located on the edge of the crater Nasmyth at the place where it was countered by the edge of the crater Phocylides.”

 

I could be wrong, but I think it’s the shared crater wall shadow creating an effect making the summit appear higher than it actually is.

 

Here are photo's I took & assembled showing them from a different angle

Photo details
Taken 4-16-2019 @ 11:20 pm
C8
25mm UO ortho with a 2x barlow
iPhone on a eyepiece adapter

 

[attachment=moon stitchedresized.jpg]

Attached Thumbnails

  • moon stitchedresized.jpg

Edited by Larrythebrewer, 14 October 2019 - 05:26 PM.

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#3 Tom Glenn

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Posted 14 October 2019 - 06:20 PM

Nice catch.  The summit is part of the shared wall between Phocylides and Nasmyth, and the shadow in your image is projecting somewhat along that shared wall, rather than entirely on the floor of Phocylides.  This actually leads to an underestimation of height if you use a trigonometry based measurement of its length (such as in LTVT, which gives an estimation of about 3000m), because the end of the shadow is being intercepted by elevated terrain.  The estimate you cite of 4000m (however obtained) is very close to the real value taken from LRO measurements, however.  Shown below is the region, viewed with the LRO Quickmap, looking south, with the peak in question marked by the white asterisk.  The elevation chart is drawn from the summit to the floor of Phocylides, and shows a differential of about 3800m.  This height value is pretty typical for many crater rim features, when measured versus the crater floor. 

 

LRO_screenshot.jpg

LRO_elevation.jpg



#4 FRANC LILL

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Posted 15 October 2019 - 10:23 AM

Thanks a lot for all your likes, John, Bill, happylimpet, j.gardavsky and Frank !

 

Larry, your remark about a visual effect is very interesring, thank you for sharing.

 

Tom, thank's for giving all your thoughts on the subject. Very nice. And specially for the LROC demonstration, I did'nt know the capabilities of that tool, I really enjoy it! (it's a shame because I will never use any more the trigonometric calculation on the moon!)  lol.gif 

 

Clear skies,

Francis


Edited by FRANC LILL, 15 October 2019 - 10:52 AM.



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