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Full Lunar Eclipse Feb 20/21 / Earth picture
scalbers
post Jan 2 2016, 03:28 PM
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Below we can see both the total and partial phases of the eclipse seen from the moon. During the partial phase the sun's disk is set to about 255 counts. During the total phase, the brightness is increased depending on how deeply in the umbra the observer is located, up to a factor of 70 for center of the umbra perspective.

Attached Image


It's interesting to see a somewhat different presentation in this actual Kaguya movie, as explained in this press release. This is an (even more) unusual situation with the brightness turned up more than in my animation, viewed by Kaguya while significantly outside the edge of the umbra. We know this by the overwhelming image brightness once the uneclipsed part of the sun rises above the moon's limb. The bright part of the sun is initially hidden by Earth/Sun rise on the moon's limb. We are seeing a more complete blue/white ring in the video at this stage than in my animation. This appears to be from scattered light in Earth's atmosphere, and isn't yet included in my posted images, as in more "normal" situations in the umbra it would be relatively faint to see next to the brighter refracted sunlight. It could be added in for completeness, on the low end of the brightness scale or in 16-bit imagery. Scattered light is a small enough component of the total so it doesn't too much affect the appearance of the moon seen from Earth. However when viewing the Earth from the moon, selected areas such as the "ring" away from the "diamond" (particularly if refracted sunlight isn't present) could have a noticeable amount, as in the Kaguya case. This is an eclipse of the sun by both Moon and Earth! I'm experimenting with a simple Rayleigh scattering addition and it looks reasonably dim. Adding Mie scattering from high altitude aerosols may boost the brightness some.

The simulation perhaps better matches some of the Surveyor eclipse imagery (bottom of link).


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DDAVIS
post Dec 15 2016, 05:25 AM
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As noted above, Lunar eclipses are a favorite subject of mine. Here is an animated study of the visual aspects of Lunar eclipses set to music I recently created. My impression of the appearance of the Earth from the Moon in such circumstances is highlighted, a sight that I hope that will one day be properly captured with a suitable high dynamic range camera.

https://vimeo.com/188736414
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scalbers
post Dec 16 2016, 01:07 AM
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Very nice and engaging presentation of the various viewpoints by DDAVIS.

With this inspiration I'm taking another look at the atmospheric scattering in the two models I've been developing. It's interesting to consider how the orange refracted sunlight merges in with the scattered (blue skylight) in the view from the moon. In most cases, the refracted sunlight is much brighter than the skylight, except they can be equivalent right in the lowest 2km or so above the Earth's limb. Another point of reference is that when we are in the center of the umbra the ring of sunlight extends up to 4km above the limb. Clouds will completely break the red ring in various places. When we are a bit off from the umbral center, then this ring has a variable thickness going above and below the 4km value.

Now with my more general "allsky" model I'm generating some views of an eclipse from the moon. The full view animation catches most of the total phase with some recent improvements. This includes some actual model clouds (for an arbitrary time) with the Earth's rotation bringing various clouds into view resulting in the shifting breaks in the red ring.

Attached Image


Here is a full view 4K animation.

The scattered light of the blue sky is barely visible given the "exposure" settings that are designed to show the sun without washing out its colors, though the animated GIFs introduce artifacts masking the sky. In the still 8K frames the faint blue counts are a good test of monitor contrast and calibration. Brightness is displayed in a linear fashion, though the "exposure" changes with each frame. Might be nice to have a display utility allowing one to easily adjust the displayed brightness from 16-bit images. That would be one way to show the HDR without changing the inherent brightness relationships.


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scalbers
post Dec 26 2016, 02:52 PM
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Below is a cropped view of an 8K animation zooming in along the Earth's limb at a scale of 1.6km per pixel, rotated 90 degrees clockwise. The first frame has the apparent sun about 45km off the limb (true sun 28km) though we're still technically in the umbra here. The edge of the umbra happens when the sun is about 85km up by the most widely used definition. We can see the sun is bright at the top where there is little extinction in the upper stratosphere. Below that is a blue layer due to ozone absorption in the lower stratosphere. The lowest part of the sun is red due to Rayleigh scattering in the lower troposphere just above the Earth's surface. The slight reddening effect of solar limb darkening isn't yet included in this model.
Attached Image


Here (click image below) is an animated crop of a 16K version that zooms in closer at 800m per pixel. The time lapse frames step every minute. The viewport shifts around the circumference of the Earth during the 3 hour period. The breaks in the ring shift noticeably even on the 1 minute time scale. This is caused by individual clouds that can be seen rising and falling in response to the Earths' rotation as if we're looking at the edge of a merry-go-round. Would be mesmerizing to see these shifting red arcs in reality.


This is a long (real-time) version. If you were actually on the moon looking through a telescope a solar filter would be advisable with a neutral density of about 2, except around 4.5 in the beginning. The upper limb of the apparent (refracted) sun slowly sinks as the actual solar limb goes farther down below the Earth's limb. Between the first 2 frames of the animation, when the actual sun and Earth limb coincide, the apparent sun reaches around 35km off the limb. An alternate definition of the umbral edge (effective or notional eclipsing layer) would be when the angular velocity of the apparent sun is half the true angular velocity. By a rough calculation this happens when the true sun is about 34km up and the apparent is 47km. The velocities get within about 10% of each other when the respective limbs are 70km and 71km up. Here is a table of the actual and apparent values.

Actual Apparent
------ --------
74km 75km
65km 67km
55km 59km
42km 51km
26km 43km
0km 35km

And just for fun here's a simulation of a lunar eclipse seen from the Earth, along with a more detailed description of all the simulations.

------------ (UPDATED DEC 28) -------------


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