Starship Asterisk*

Green Flash at Moonrise

Explanation: Follow a sunset on a clear day against a distant horizon and you might glimpse a green flash just as the Sun disappears, the sunlight briefly refracted over a long sight-line through atmospheric layers. You can spot a green flash at sunrise too. Pinpointing the exact place and time to see the rising Sun peeking above the horizon is a little more difficult though, and it can be harder still to catch a green flash from the fainter rising Moon. But well-planned snapshots did record a green flash at the Full Moon's upper edge on June 2nd, from the Roque de los Muchachos Observatory on the Canary Island of La Palma. Looking a little south of due east, this long telephoto view finds the rising Moon above mountains and a sea of clouds. In sunlit profile are the mountaintop Teide Observatory telescope domes on the island of Tenerife some 143 kilometers away.

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The Man in the Moon is wearing his green nightcap.

Ann

Somehow when I looked at this earlier I thought oh, another green flash. Only much later did I realize it was a rare moon green flash. I may as well be blind, sometimes.

Remarkable. One did not even know that such existed.

Merci!

I didn't know the moon also exhibited a green flash. Are they partly due to airglow?

geckzilla wrote:Somehow when I looked at this earlier I thought oh, another green flash. Only much later did I realize it was a rare moon green flash. I may as well be blind, sometimes.

Me too!

starsurfer wrote:I didn't know the moon also exhibited a green flash. Are they partly due to airglow?

I would expect that it's due to the same refractive dispersion than causes the solar green flash. Airglow wouldn't affect such a localized area, and wouldn't be discernible during sunset anyway.

starsurfer wrote:I didn't know the moon also exhibited a green flash. Are they partly due to airglow?

Virtually every optical phenomenon we encounter with the Sun occurs with the Moon as well, for exactly the same reasons, just a half million times dimmer. So I doubt airglow has anything to do with it.

Great embroidery picture, Ann.
And really amazing capture in the APOD image, Daniel Lopez!
For a moment, I thought I was looking at an image of light that had passed through Earth's atmosphere twice. But then I realized that this would not generally be true. But, when we (on Earth) see a dim moon in full eclipse, then we are looking at light that has passed through Earth's atmosphere, twice, right?

MarkBour wrote:But, when we (on Earth) see a dim moon in full eclipse, then we are looking at light that has passed through Earth's atmosphere, twice, right?

I guess it depends on how you define "twice". The light that is illuminating the eclipsed Moon has largely passed from the outer atmosphere, down some ways, and then back out again. The actual path length through the atmosphere, however, can be many times longer than the height of the atmosphere.

Maybe a better example of light passing twice through Earth's atmosphere is moonshine, where you actually have sunlight shining down through about one atmospheric height, bouncing off the ocean, and then passing back through the atmosphere to illuminate the Moon.

Maybe a better example of light passing twice through Earth's atmosphere is moonshine, where you actually have sunlight shining down through about one atmospheric height, bouncing off the ocean, and then passing back through the atmosphere to illuminate the Moon.

I think I see your point. But I'm not following your second example. Do you mean Earthshine, as observed on the Moon or a spacecraft? That sounds like the path you describe. Or are you giving a phenomenon observable from the ground on the Earth? In that case, I don't get it.

MarkBour wrote:

Maybe a better example of light passing twice through Earth's atmosphere is moonshine, where you actually have sunlight shining down through about one atmospheric height, bouncing off the ocean, and then passing back through the atmosphere to illuminate the Moon.

I think I see your point. But I'm not following your second example. Do you mean Earthshine, as observed on the Moon or a spacecraft? That sounds like the path you describe. Or are you giving a phenomenon observable from the ground on the Earth? In that case, I don't get it.

True, as I described it, that would be earthshine seen from space. From the ground we're seeing light that has made three passes through the atmosphere.

Well, whether coming from the Moon or from the Sun, it's all sunlight after all

Cheers,
Rogelio

What a wonderful and intriguing picture... and WE have an APOD friend who lives on Tenerife...
MargaritaMc... so 'ELLO, M!!!

The constants of Science. Same process, same phenomena...different objects...something is Consistent...

Is it the way the atmosphere splits up the light to hit just those frequencies?

:---[===] *

It is a fascinating image and particularly so because the "long telephoto view" was taken from 143 kilometers away, which is nearly 90 miles! That's amazing (well it is to me, though nobody else has so far thought it worth commenting on). Click on the "143 kilometers away" link for a map.

DavidLeodis wrote:It is a fascinating image and particularly so because the "long telephoto view" was taken from 143 kilometers away, which is nearly 90 miles! That's amazing (well it is to me, though nobody else has so far thought it worth commenting on). Click on the "143 kilometers away" link for a map.

But... the Moon is 2700 times farther away than that. Talk about a "long telephoto view"!