# Why does the moon 'peel' away from the horizon in this photograph?

The Himawari-8 geostationary weather satellite recently had a lunar intrusion into it's primary sensor (the Advance Himawari Imager, or AHI):

Zooming in on the moon:
I see a strange cupping (or 'peeling') of the moon away from the horizon:

My question is: what is the explanation for this 'peeling' aberration?

1. At the time of day of the photograph, we see the Earth with ~5 degrees of longitude in night. The Earth presents approximately 17 degrees across from GEO, so the moon is $$17^{\circ}/2=8.5^{\circ}$$ degrees away from nadir, and so I expect the moon to have $$5^{\circ}+8.5^{\circ}= 13.5^{\circ}$$ of longitude in night. With barely half the moon peaking out above the Earth's horizon, the terminator is well behind the Earth.
2. The cupping aberration appears equal on both edges. The Sun is in the top right corner of the picture, and so I would expect a terminator related effect to be more pronounced on the bottom of the moon than the top.
• Why would this include the terminator? This strongly looks like atmospheric refraction. You see similar effects during the Sun-Venus transit, just before Venus enters the solar disc, due to the atmosphere of Venus. May 15 '19 at 23:30
• It looks like this phenomenon: blogs.discovermagazine.com/badastronomy/2012/05/07/… , blogs.discovermagazine.com/badastronomy/2011/09/12/… , blogs.discovermagazine.com/badastronomy/2011/01/21/… but more extreme (due to the greater distance of Himawari-8 vs ISS? - I haven't done the math). Note that the part of Mare Imbrium closest to the limb looks cut off and replaced with a bright area. That could be a squished image of the the part of the moon below the horizon. May 16 '19 at 3:52
• slightly related only Refraction by Saturn's atmosphere - how dense is it here? Can you please add a link to the original Himawari image so that it can be verified that it is real? There have been questions about images in the past that turned out to be not real. Thanks!
– uhoh
May 16 '19 at 7:06
• Actually I can verify it. I went to himawari8.nict.go.jp and set the time to 2019-05-15 08:00:00 (it's local time and I am in UTC +8) and there it is, cool! :-) i.stack.imgur.com/PAJPO.jpg
– uhoh
May 16 '19 at 7:16

Looks like an inferior mirage to me.

This:

https://aty.sdsu.edu/explain/simulations/inf-mir/Kaplan_photos.html

Has a work through for the disk of the sun but I think the same general principles apply here as well.

The specific effect will be somewhat different since in the image from space rays are moving from space down into and through the atmosphere, and then back up again, whereas in the image below the rays terminate at the Earth's surface.

Simulation and photograph from Andrew T. Young's page Photographs of an Inferior-Mirage Sunset:

The inferior mirage is very clearly shown in a series of sunset images taken by George Kaplan, of the U. S. Naval Observatory. Here, I describe what's seen in these images, which are actually on the Naval Observatory's website. They are such a “textbook example” of the inferior-mirage sunset that I begged for some details, and permission to show the images here.

• Excellent find! Since links rot and break over time, so I've pulled in a few images and credited both Andrew Young's work and the photos by George Kaplan, of the U. S. Naval Observatory.
– uhoh
May 16 '19 at 21:26