13 replies to this topic

[RobDob]

I became fascinated with this subject after noticing some yellow/green artifact bands from some of my iPhone images of the eclipse (see my image in post #2). This led me to research this topic and I found that there really isn't a lot of info or images out there about the Lunar Total Eclipse 'Rainbow Moon' effect. Now, with a proliferation of modern cameras and telescopes aimed at the moon, we can get more photographic and visual data. I did find a few links and a very informative NASA video:

 

https://www.pbs.org/...e-lunar-eclipse

 

https://science.nasa...ep_lunareclipse

 

https://www.foxweath...l-lunar-eclipse Here's a quote from Seminole State College Astronomy Director Derek Demeter:
"Demeter says if you can look at the moon during the eclipse through a telescope, you might see more than red. "You can actually see on the very edges of the moon, a blue light, then an orange light, a yellow light. You see all the colors of a rainbow," he explains. "So really a total eclipse moon should be called a rainbow unicorn moon because, actually, you see all the colors of the rainbow, cast on the moon because a portion of the white light that is split into the colors of the rainbow can be seen on the moon.""

 

https://svs.gsfc.nasa.gov/14143 - Pay attention to the section at 1 minute

 

What causes a Rainbow Moon? It occurs when the moon just enters or starts to exit totality during a total lunar eclipse. The earth's atmosphere scatters light and casts a rainbow shadow onto the moon during these few minutes that the moon transitions through totality.

 

Disclaimer: I compiled these images from the web, and with permission, from some fellow CN members. The color saturation I used in GIMP may be considered pretty aggressive and may represent some false color enhanced from the original images' processing. I tried to use only enough saturation to show undeniably that there is a rainbow pattern eeked out from the original images' color profile.

 

To future rainbow moon observing!
Rob

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Edited by RobDob, 24 May 2022 - 02:05 AM.

[RobDob]

Here's some from fellow CN members:

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Edited by RobDob, 23 May 2022 - 03:06 PM.

[ETXer]

I've been looking forward to this post! I wish I had seen some of this information before this eclipse, I would have paid much more attention to the color progression. Even though the images have been "enhanced," the results are consistent with each other. I know I'll be looking for this effect with next November's event.

Edited by ETXer, 23 May 2022 - 08:00 PM.

[Organic Astrochemist]

https://svs.gsfc.nasa.gov/14143 - Pay attention to the section at 1 minute

What causes a Rainbow Moon? It occurs when the moon just enters or starts to exit totality during a total lunar eclipse. The earth's atmosphere acts like a prism and casts a rainbow shadow onto the moon during these few minutes that the moon transitions through totality.


To future rainbow moon observing!
Rob

I think this is a little complicated so one has to try to be precise. The video doesn’t actually say refraction, like what happens with a prism. Instead, it talks about scattering. With scattering, blue light is scattered way more than longer wavelengths. Red is scattered the least and presumably that’s why during totality some of the red light makes it to the moon and none of the blue light does.

I don’t really like that graphic because it makes it look like red light is getting scattered the most to bend around the earth and hit the moon.

There may also be refraction (like in a prism) but this video doesn’t mention that. Again blue light should have the higher refractive index (be bent more) and red light less.

I don’t really know the relative importance of scattering vs refraction.

But I don’t think there are many images with the limb of the moon in only green, only yellow, or only orange. Mostly just white, blue and red/orange. So I’m not sure the moon is passing through a big beam of refracted light of different colors like from a rainbow or a prism.

I also think that as the directly illuminated limb of the moon gets very small it actually gets brighter and this fools a lot of photographers who overexpose this limb, which can cause color artifacts.

Edited by Organic Astrochemist, 23 May 2022 - 11:57 PM.

[RobDob]

I think this is a little complicated so one has to try to be precise. The video doesn’t actually say refraction, like what happens with a prism. Instead, it talks about scattering. With scattering, blue light is scattered way more than longer wavelengths. Red is scattered the least and presumably that’s why during totality some of the red light makes it to the moon and none of the blue light does.

I don’t really like that graphic because it makes it look like red light is getting scattered the most to bend around the earth and hit the moon.

There may also be refraction (like in a prism) but this video doesn’t mention that. Again blue light should have the higher refractive index (be bent more) and red light less.

I don’t really know the relative importance of scattering vs refraction.

But I don’t think there are many images with the limb of the moon in only green, only yellow, or only orange. Mostly just white, blue and red/orange. So I’m not sure the moon is passing through a big beam of refracted light of different colors like from a rainbow or a prism.

I also think that as the directly illuminated limb of the moon gets very small it actually gets brighter and this fools a lot of photographers who overexpose this limb, which can cause color artifacts.

Thanks for your insight. I corrected the description. Yes, I would love to find a detailed and accurate scientific description of what's going on, but this all that Google offered me, so whether it be right or wrong, I based my laymen's description on what I could find. I think, although way out of scale, the video does convey the conceptual idea of what is happening.

 

Edit: I agree regarding the overexposed limb, as I experienced color artifacts as you mention. I hope to get more images in the future to find any color trends verses limb exposure.

Edited by RobDob, 24 May 2022 - 02:04 AM.

[Reconnaissance]

I noticed the rainbow effect and hadn’t ever seen it before in my telescope/eyepiece combination (ETX 90 25mm Plossl). I was concerned something had happened to damage or shift the optics in my scope. I was out this morning looking at Saturn and didn’t see the effect, so I chalked it up as some sort of anomaly….then I read about the others’s experiences and have new understanding!

[Borodog]

I don’t really like that graphic because it makes it look like red light is getting scattered the most to bend around the earth and hit the moon.

 

That is exactly what is happening. Seen from the Moon, the Earth is roughly 3.7 times the apparent diameter of the Sun. In deep eclipse there is no way there is a refracted image of the Sun visible at the limb of the Earth. It can only be scattered light.

[RobDob]

Found some more interesting images off the interwebs. This one from Space.com showing the start, middle, and end of totality from 2019 lunar eclipse. I thought it would also be interesting to reverse the order and try to visualize the Earth's shadow superimposed over all 3 stages of totality.

 

Rob

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Edited by RobDob, 26 May 2022 - 01:32 AM.

[KBHornblower]

If I am not mistaken, it is incorrect to say that the reddish light in the umbra does not include refracted light directly from the Sun.  Incoming rays in clear air are refracted about 0.5 degree before grazing the surface.  My reasoning is that this light is refracted another 0.5 degree on the way back out, for a total of a full degree.  This is plenty to cover the whole umbra.  It is partially blocked by varying amounts of dust and clouds, so the brightness varies from one eclipse to the next.

 

I think the bluish tint at the edge of the umbra has something to do with absorption and scattering characteristics of the upper atmosphere.

[RobDob]

I think the bluish tint at the edge of the umbra has something to do with absorption and scattering characteristics of the upper atmosphere.

There is a brief description about the ozone layer causing the bluish tint, or referred to as a turquoise color in this link referring to a lunar eclipse back in 2014:

https://www.pbs.org/...e-lunar-eclipse

Edited by RobDob, 26 May 2022 - 10:37 PM.

[BillHarris]

This last photo is something that I've considered for years-- using the moving Moon to "map" the Earth's shadow.
Now that we have video capabilities we could track on the Earth's shadow and video the Moon moving West to East, or track on the Moon with a Lunar rate and video the motion of the shadow. The resulting 100 minute video could be edited to speed it up or stop-motion it to give a nice presentation.

--Bill

[Organic Astrochemist]

If I am not mistaken, it is incorrect to say that the reddish light in the umbra does not include refracted light directly from the Sun. Incoming rays in clear air are refracted about 0.5 degree before grazing the surface. My reasoning is that this light is refracted another 0.5 degree on the way back out, for a total of a full degree. This is plenty to cover the whole umbra. It is partially blocked by varying amounts of dust and clouds, so the brightness varies from one eclipse to the next.

I agree that this is more of a both/and kind of phenomenon rather than either refraction or scattering.

“The dominant radiative-transfer mech- anisms are selective molecular absorption, Rayleigh scattering as well as refraction.”

https://arxiv.org/pdf/2002.08690.pdf

[Borodog]

If I am not mistaken, it is incorrect to say that the reddish light in the umbra does not include refracted light directly from the Sun.  Incoming rays in clear air are refracted about 0.5 degree before grazing the surface.  My reasoning is that this light is refracted another 0.5 degree on the way back out, for a total of a full degree.  This is plenty to cover the whole umbra.  It is partially blocked by varying amounts of dust and clouds, so the brightness varies from one eclipse to the next.

 

I think the bluish tint at the edge of the umbra has something to do with absorption and scattering characteristics of the upper atmosphere.

I believe you are correct! The angular size of the Earth from the Moon is ~1.85 degrees. The angular size of the sun is ~0.5 degrees. If the sun were directly behind the center of the Earth, it would be ~0.7 degrees from the edge. Refraction at grazing incidence is indeed about 0.5 degrees, as you point out, and you are correct that you will get this effect coming and going. Hence the illumination of the Moon during a total eclipse could indeed be from a refracted image of the sun around the perimeter of the Earth. That's astonishing, really.

 

Thank you for correcting my mistake. I'm really happy to have learned this tonight.

Edited by Borodog, 27 May 2022 - 10:37 PM.

[bill w]

pushed the saturation on one of mine, just after total eclipse:

 

thanks for the post

i'd been looking for green on this, but in the wrong place.  expected it above the blue. 

there's a hint of green below, but the levels are actually equal to the blue. 

will check out some of the earlier images

 

a nasa site mentions another phenomenon: preferential absorption of red light by ozone in the upper atmosphere.

(alluded to by organic astrochemist)

so there are 3 potential color phenomena:

frequency dependent atmospheric refraction--with which all high mag planetary imagers are familiar

preferential scattering of shorter wavelength light

preferential absorption of red light in the upper atomsphere

Edited by bill w, 28 May 2022 - 09:16 PM.