APOD: Full Moon in Mountain Shadow (2016 Oct 21)

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APOD: Full Moon in Mountain Shadow (2016 Oct 21)

Post by APOD Robot » Fri Oct 21, 2016 4:07 am

Image Full Moon in Mountain Shadow

Explanation: On October 15, standing near the summit of Hawaii's Mauna Kea and looking away from a gorgeous sunset produced this magnificent snapshot of a Full Moon rising within the volcanic mountain's shadow. An alignment across the Solar System is captured in the stunning scene and seeming contradiction of bright Moon in dark shadow. The triangular appearance of a shadow cast by a mountain's irregular profile is normal. It's created by the perspective of the distant mountaintop view through the dense atmosphere. Rising as the Sun sets, the antisolar point or the point opposite the Sun is close to the perspective's vanishing point near the mountain shadow's peak. But extending in the antisolar direction, Earth's conical shadow is only a few lunar diameter's wide at the distance of the Moon. So October's Full Hunters Moon is still reflecting sunlight, seen through the mountain's atmospheric shadow but found too far from the antisolar point and the Earth's extended shadow to be eclipsed.

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Ann
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Re: APOD: Full Moon in Mountain Shadow (2016 Oct 21)

Post by Ann » Fri Oct 21, 2016 4:08 am

Am I right that APOD has previously featured an image that was extremely similar to this one?

In any case, it is a stunning image.

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Re: APOD: Full Moon in Mountain Shadow (2016 Oct 21)

Post by heehaw » Fri Oct 21, 2016 8:46 am

It might be nice to add a roll-over showing the circle of the Earth's shadow at the distance of the Moon. It is a nice picture indeed!

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Re: APOD: Full Moon in Mountain Shadow (2016 Oct 21)

Post by geckzilla » Fri Oct 21, 2016 11:46 am

Ann wrote:Am I right that APOD has previously featured an image that was extremely similar to this one?
Yes, here's another one:
http://apod.nasa.gov/apod/ap150503.html

Today's captures a wider angle. To stand there and see it with one's own eyes must be wonderful.
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Re: APOD: Full Moon in Mountain Shadow (2016 Oct 21)

Post by MarkBour » Fri Oct 21, 2016 7:08 pm

That is a lovely photo and totally messes with my intuition.
Earth's atmosphere is acting like a partially-silvered mirror.
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Re: APOD: Full Moon in Mountain Shadow (2016 Oct 21)

Post by neufer » Sat Oct 22, 2016 1:12 am


MarkBour wrote:
That is a lovely photo and totally messes with my intuition. Earth's atmosphere is acting like a partially-silvered mirror.
As an obliquely viewed 3-D shadow unusual to our everyday experience the photo messes with most of our intuitions.

However, it is definitely NOT acting like a partially-silvered mirror and the observed pyramidal shape has more to due with a Star Wars opening crawl than to an accurate image of the mountain.
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Re: APOD: Full Moon in Mountain Shadow (2016 Oct 21)

Post by MarkBour » Mon Oct 24, 2016 5:10 pm

neufer wrote:However, it is definitely NOT acting like a partially-silvered mirror and the observed pyramidal shape has more to due with a Star Wars opening crawl than to an accurate image of the mountain.
I think we're focusing on different aspects of this image. You're talking mostly about the shadow. I'm talking about two different sources of light in the image.
labelled.jpg
The light that is producing the upper band (labelled "1") is being reflected back (you might prefer scattered back?) whereas within the mountain's shadow, where there is not so much reflected light, one can see the Moon (labelled "2"), whose light is coming to us from beyond our atmosphere, straight through the atmosphere to us.

(By the way, I assume the light hitting the Moon from the Sun did not first go through Earth's atmosphere on the way to the Moon, except for some exceedingly tiny fraction of it.)
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Re: APOD: Full Moon in Mountain Shadow (2016 Oct 21)

Post by Chris Peterson » Mon Oct 24, 2016 5:45 pm

MarkBour wrote:
neufer wrote:However, it is definitely NOT acting like a partially-silvered mirror and the observed pyramidal shape has more to due with a Star Wars opening crawl than to an accurate image of the mountain.
I think we're focusing on different aspects of this image. You're talking mostly about the shadow. I'm talking about two different sources of light in the image.
labelled.jpg
The light that is producing the upper band (labelled "1") is being reflected back (you might prefer scattered back?) whereas within the mountain's shadow, where there is not so much reflected light, one can see the Moon (labelled "2"), whose light is coming to us from beyond our atmosphere, straight through the atmosphere to us.
It's still not acting like a partially silvered mirror- for a reason that you've actually identified. Mirrors exhibit specular reflection. Reflection and scatter are not the same things. Yes, the atmosphere both backscatters and transmits light. But there's nothing specular about what's going on, so any usage of "mirror" makes little sense.
Chris

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Re: APOD: Full Moon in Mountain Shadow (2016 Oct 21)

Post by neufer » Mon Oct 24, 2016 5:49 pm

MarkBour wrote:
neufer wrote:
MarkBour wrote:
Earth's atmosphere is acting like a partially-silvered mirror.
It is definitely NOT acting like a partially-silvered mirror and the observed pyramidal shape has more to due with a Star Wars opening crawl.
I think we're focusing on different aspects of this image. You're talking mostly about the shadow. I'm talking about two different sources of light in the image. The light that is producing the upper band is being reflected back (you might prefer scattered back?) whereas within the mountain's shadow, where there is not so much reflected light, one can see the Moon, whose light is coming to us from beyond our atmosphere, straight through the atmosphere to us.
So you are saying that we can both easily directly see Moon light and indirectly see Sun light.

The fact that we see an actual image of the Moon but not an image of the Sun speaks against a partially-silvered mirror suggestion(; yes, I prefer scattered back) .
MarkBour wrote:
(By the way, I assume the light hitting the Moon from the Sun did not first go through Earth's atmosphere on the way to the Moon, except for some exceedingly tiny fraction of it.)
http://www.skyandtelescope.com/astronomy-news/observing-news/eclipses-in-2016-012220165/ wrote:
Solar and Lunar Eclipses in 2016
By: Kelly Beatty | Sky and Telescope January 22, 2016

<<This year there's a total solar eclipse on March 9th (visible from Indonesia) and an annular on September 1st (central Africa). But the terrific "tetrad" of total lunar eclipses is over — we'll see just two barely-there penumbral eclipses, on March 23rd and September 16th.>>
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Re: APOD: Full Moon in Mountain Shadow (2016 Oct 21)

Post by MarkBour » Mon Oct 24, 2016 7:40 pm

Chris Peterson wrote:Reflection and scatter are not the same things. Yes, the atmosphere both backscatters and transmits light. But there's nothing specular about what's going on, so any usage of "mirror" makes little sense.
neufer wrote:The fact that we see an actual image of the Moon but not an image of the Sun speaks against a partially-silvered mirror suggestion(; yes, I prefer scattered back) .
Got it ... thanks.
Mark Goldfain