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Bad Moon Rising, and invisible eclipse, July 4, 2020

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#1 Tom Glenn

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Posted 05 July 2020 - 04:18 AM

I took a few photographs of the Moon using a DSLR (Nikon D5600) to document tonight's Full Moon and anticlimactic penumbral eclipse.  The first one below shows the Moon emerging behind a mountain after dark.  This was taken using a Nikon 70-200mm lens, handheld, at 200mm and f/8, ISO 800, 1/250s.  The image in the following post compares the Moon at 04:31UT (maximum eclipse) with a photo taken two hours later, at 06:36UT, after the eclipse was over.  More information on that follows in the next post. 

 

Bad_Moon_Rising_July4_2020_TG.jpg


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#2 Tom Glenn

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Posted 05 July 2020 - 04:19 AM

To minimize the influence of processing, I used the same exposure settings for both photographs, 200mm, f/5.6, ISO 100, 1/500s, and took the jpegs straight from the camera.  This produces a significant difference in coloration and brightness between the two images, because of the changing elevation above the horizon.  To attempt to normalize this, I converted both images to grayscale, and then adjusted the exposures to match.  However, it is actually impossible to perfectly match the exposures because of these atmospheric variables.  Nevertheless, this does demonstrate that the difference between the two images is minimal.  You could perhaps believe that the north polar region is somewhat dimmer during the maximum eclipse (and indeed it does measure as such), however, these differences are very small and would have to be measured under more controlled conditions to verify, with the Moon higher in the sky, and using a more rigorous imaging approach (which I often do, but not in this case because I could barely even see the Moon from my house).  To summarize, it would be hopeless to detect any changes visually during the eclipse.  

 

eclipse_edit_TG.jpg


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#3 MarkGregory

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Posted 05 July 2020 - 04:53 AM

I took a few photographs of the Moon using a DSLR (Nikon D5600) to document tonight's Full Moon and anticlimactic penumbral eclipse.  The first one below shows the Moon emerging behind a mountain after dark.  This was taken using a Nikon 70-200mm lens, handheld, at 200mm and f/8, ISO 800, 1/250s.  The image in the following post compares the Moon at 04:31UT (maximum eclipse) with a photo taken two hours later, at 06:36UT, after the eclipse was over.  More information on that follows in the next post. 

 

attachicon.gifBad_Moon_Rising_July4_2020_TG.jpg

Interesting, several years ago I shot some photos of a penumbras eclipse and the color of the moon photos were just like yours. Cool. I’ll post a shot a little later for comparison. Mark

 

7335001466_f726192417_c.jpg


Edited by MarkGregory, 05 July 2020 - 02:50 PM.


#4 Tom Glenn

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Posted 05 July 2020 - 05:07 AM

Interesting, several years ago I shot some photos of a penumbras eclipse and the color of the moon photos were just like yours. Cool. I’ll post a shot a little later for comparison. Mark

Mark, thanks.  It's important to note, however, that the coloration of the first photo is simply due to the low elevation of the Moon above the horizon (less than 10 degrees in this case), and has nothing whatsoever to do with the eclipse.  A photo like this would have the same coloration at any Full Moon.  In the second photo, comparing the two Moons, I intentionally removed the color and equalized the exposures because the raw images would be misleading.  From my location, the maximum eclipse occurred with the Moon very low in the sky, giving it a red shifted color, but again, this had nothing to do with the eclipse.  



#5 MarkGregory

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Posted 05 July 2020 - 08:33 AM

10/4. I just found it interesting that we shot the eclipses and ended up with similar colors. 



#6 Tom Glenn

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Posted 06 July 2020 - 03:14 AM

Just to highlight some of the difficulties in comparing photographs taken at different times, here are the raw (unaltered jpegs, actually) exposures from my images above.  The difference in coloration and brightness has nothing to do with the eclipse, although there is still a potential dimming in the northern regions of the Moon that can be barely detected in the normalized exposures presented earlier.  

 

eclipse_raw_TG.jpg



#7 Tom Glenn

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Posted 07 July 2020 - 04:46 AM

OK, I've gone back and analyzed my data more carefully.  It's a pity that this eclipse didn't present itself in more favorable circumstances to allow more careful analysis, but this is the best I can present with my data.  I took ten photographs during the maximum eclipse, as well as two hours later, after the eclipse was over.  I have now stacked each set of ten images to improve the SNR of each image.  However, before stacking the images, I imported the raw NEF files (Nikon) into the program RawTherapee, and then exported tiffs that corresponded to linear color profiles, with no tone curves added.  It's important to realize that when working with jpegs, or even with raw files opened in a raw editor like Adobe Camera Raw, there are nonlinear tone curves applied to the image whether you realize it or not, before you even see it.  This can complicate exposure adjustments.  I stacked the raw linear files and then converted the resulting stacks to grayscale images in Photoshop and then normalized the exposures.  The image captured during maximum eclipse, which was low on the horizon, required an exposure increase of 0.35EV to equal the exposure of the image captured two hours later using the same camera settings.  I then made an animation of the resulting images.  This showed a clear darkening of the north polar region during the eclipse.  Shown below are two animations.  The first corresponds to the linear images, transformed into sRGB color space, but without any additional modifications of the tone curve.  These images appear much more bland than standard images from a camera (either jpeg or processed raw images).  The second animation is with an additional contrast boost added.  Both animations show clear darkening in the eclipsed region, with essentially no changes in other regions of the Moon.  The only odd finding is that the region directly north of Mare Crisium, which should be impacted by the eclipse, does not demonstrate any darkening.  Also of interest is that you can clearly see the effects of diurnal libration, as the Earth rotates and my vantage position on the Moon changes slightly, causing an apparent rotation of the Moon.  Other slight differences in the two images, such as sharpness, are caused by the changing conditions and altitude over the two hour period.  

 

Eclipse_July4_2020_TG.gif

 

Eclipse_July4_2020_TG_high_contrast.gif


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