APOD: Eclipsed Moonlight (2011 Jun 21)

Comments and questions about the APOD on the main view screen.
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APOD: Eclipsed Moonlight (2011 Jun 21)

Post by APOD Robot » Tue Jun 21, 2011 4:07 am

Image Eclipsed Moonlight

Explanation: A celestial prelude to today's solstice, the June 15 total lunar eclipse was one of the longest in recent years. It was also one of the darkest, but not completely dark. Even during totality, a somber, red lunar disk could be seen in the starry night sky, reflecting reddened light falling on to its surface. Seen from a lunar perspective, the ruddy illumination is from all the sunsets and sunrises around the edges of a silhouetted Earth. In this sharp portrait of the eclipsed Moon from Granada, Spain, the Moon's edge reflects a bluish tinge as well as it emerges from Earth's umbral shadow. The bluer light is still filtered through Earth's atmosphere, but originates in rays of sunlight passing through layers high in the upper stratosphere. That light is colored by ozone that absorbs red light and transmits bluer hues.

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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by alter-ego » Tue Jun 21, 2011 4:37 am

In Feb 2009, the lunar explorer Kaguya took this HD lunar-perspective picture (see also here for better description). The color accuracy may be questionable, but the blue illumination source is significant, and Kaguya's location corresponds to the pertinent bluish region in the APOD. Interestingly, it appears this picture was not shown as an APOD. By itself, it may lack the wow factor but it does make a good sidekick for today's APOD.
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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by Beyond » Tue Jun 21, 2011 4:55 am

Gads! I must be blinder than two bats. I think it's been twice now, that a blue tinge was mentioned, but i haven't seen any blue at all. :? :?
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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by Indigo_Sunrise » Tue Jun 21, 2011 10:42 am

Beyond, maybe it's more of a 'comparison' thing, as in: compared to the rest of the lunar surface in the image, the area approximately 7, 8 and maybe even 9 o'clock-ish are blue-er in color than the rest of the disk....?
But don't worry, you're not alone in not seeing the blue referred to in the description - I think it looks more gray-ish than blue, maybe even with a tinge of lavender! But I've also read somewhere that color can be subjective :lol:


However, nice image!

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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by orin stepanek » Tue Jun 21, 2011 12:21 pm

Beyond wrote:Gads! I must be blinder than two bats. I think it's been twice now, that a blue tinge was mentioned, but i haven't seen any blue at all. :? :?
It does to me Beyond; but that;s my perspective. Anyway it does make a good wallpaper. 8-)
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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by Beyond » Tue Jun 21, 2011 1:06 pm

I did see a nice looking blue once. But it was a picture of the earth from space, the ISS i think, where there was a blue patch on the north horizon, like the green patch you can sometimes get from the setting sun.So i guess i just have a narrower view of color.Oh-well, dats just the way it is. :|
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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by Ann » Tue Jun 21, 2011 3:00 pm

The lower left part of the Moon in today's APOD looks blue to me. What a surprise. :wink:

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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by rstevenson » Tue Jun 21, 2011 4:05 pm

Ann wrote:The lower left part of the Moon in today's APOD looks blue to me. What a surprise. :wink:
My colour picker (which lets me see at the pixel level) can't find any blue, but theres lots of purple there. A Royal Moon!

Rob

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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by Chris Peterson » Tue Jun 21, 2011 4:36 pm

rstevenson wrote:
Ann wrote:The lower left part of the Moon in today's APOD looks blue to me. What a surprise. :wink:
My colour picker (which lets me see at the pixel level) can't find any blue, but theres lots of purple there. A Royal Moon!
Many people would consider purple to be a type of blue. That is, there are colors in the blue purple range that will be called "purple" by some and "blue" by others.

A proper color sampling tool will show the native colors, which in this case are red, green, and blue (but not purple). And if you look at the crescent area on the lower left, the intensity of the blue signal is significantly higher than the red or green- with a shift towards equal red and blue near the terminator, and a dominant red signal in the shadowed area. So regardless of how this might appear on any particular monitor (most of which are probably uncalibrated), the underlying data makes it clear that the sunlit region can reasonably be considered blue.
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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by rstevenson » Tue Jun 21, 2011 5:06 pm

Chris Peterson wrote:A proper color sampling tool will show the native colors, which in this case are red, green, and blue (but not purple).
As I said, I used such a tool -- a "proper" one. (And my monitor is calibrated; it has to be for the work I do.) The purple I was referring to could be from any of a large number of pixels, but they're all in the range of about RGB 50%/50%/60%. So yes, there's slightly more blue in those pixels than red or green, but the result is purple, not blue. I can't find a single pixel that reads anywhere near 0%/0%/100%.

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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by Chris Peterson » Tue Jun 21, 2011 5:21 pm

rstevenson wrote:As I said, I used such a tool -- a "proper" one. (And my monitor is calibrated; it has to be for the work I do.) The purple I was referring to could be from any of a large number of pixels, but they're all in the range of about RGB 50%/50%/60%. So yes, there's slightly more blue in those pixels than red or green, but the result is purple, not blue. I can't find a single pixel that reads anywhere near 0%/0%/100%.
Right. But 50/50/60 is reasonably called blue. It's a different blue than 0/0/100, but when we restrict our colors to eight or ten names, there is a wide range of "blue" in the available gamut.

Subjectively, on my calibrated monitor I definitely wouldn't call the blue area purple or violet. It is a purplish blue, for sure, but if I had to give it a ROYGBIV name, it would be blue, not violet.
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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by islader2 » Tue Jun 21, 2011 7:26 pm

What blue? By me! But I am not out of this posting due to my handicap: anisotrophia. But I am in good company--the condition is also called DALTONISM.

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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by Ann » Tue Jun 21, 2011 7:26 pm

rstevenson wrote:
The purple I was referring to could be from any of a large number of pixels, but they're all in the range of about RGB 50%/50%/60%.
50% red, 50% green, and 60% blue?

Forgive my levity (and, no doubt, my ignorance), but this reminds me of a student blooper I came across once upon a time. It went something like this:

Handel was half Italian, half German, and half English. He was very large.
Hmmm... he was indeed quite large.

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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by Chris Peterson » Tue Jun 21, 2011 7:42 pm

Ann wrote:50% red, 50% green, and 60% blue?
Thank you for pointing out something that could confuse people not use to working with colors. So to be clear, what these values mean is the relative intensity of each. So 50/50/60 means that red is at 50% of its maximum intensity, green is at 50% of its maximum intensity, and blue is at 60% of its maximum intensity.

0/0/0 is black
50/50/50 is 50% gray
100/100/100 is white
50/50/60 is a medium gray with a blue cast (a low saturation blue).
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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by rstevenson » Tue Jun 21, 2011 7:43 pm

50% red, 50% green, and 60% blue?
I can only report what my software said. :mrgreen:

But it only seems odd. What it means (I think) is that that particular pixel has 50% of the possible 100% red, 50% of the possible green, and 60% of the possible blue. No attempt is made to get them to add up to 100% all together.

It could also report it as an 8-bit value, where each number is on a scale from 0 to 240, or as hex values, and so on. But I thought the percentage one was easier to grasp. If I had downloaded the image and opened it in PhotoShop I could have reported the colour in CMYK, but there's a limit to how much time I want to spend on the difference between purple and blue -- a difference which mostly exists between our ears anyway. :twisted:

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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by Chris Peterson » Tue Jun 21, 2011 7:52 pm

rstevenson wrote:It could also report it as an 8-bit value, where each number is on a scale from 0 to 240, or as hex values, and so on.
In that case, the value will normally be from 0-255 (or 0-FF for hex), which is the full 8-bit range.
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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by rstevenson » Tue Jun 21, 2011 9:26 pm

255, you're right. You can tell how seldom I use that scale.

Now, what was this thread about? Oh yeah, blue cheese.

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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by alter-ego » Wed Jun 22, 2011 3:27 am

rstevenson wrote:255, you're right. You can tell how seldom I use that scale.

Now, what was this thread about? Oh yeah, blue cheese.

Rob
I'd say the take away from all this is that visual subtlety most often accompanies colors described with a tinge of "ish".

Hey... I thought we were talking about green cheese
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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by Beyond » Wed Jun 22, 2011 3:46 am

Isn't the moon made out of yellow cheese?? Anyway, so some where back up the posts, blue-gray was mentioned. So apparently my vision doesn't go too far into the lower percentages of blue before they look gray to me. So if i ever come upon 'once-in-a-blue-moon', i'll miss it and not even know it. :lol:
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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by Indigo_Sunrise » Wed Jun 22, 2011 10:35 am

Beyond wrote:So if i ever come upon 'once-in-a-blue-moon', i'll miss it and not even know it. :lol:

No you won't, Beyond: we'll be sure to post about it, or even send you a message-reminder!

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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by DavidLeodis » Wed Jun 22, 2011 12:01 pm

In the explanation it states "the Moon's edge reflects a bluish tinge as well as it emerges from Earth's umbral shadow". That seems to me to imply that the Moon was appearing to move to the left, but when seen from the Earth it appears to move across to the right. I accept that I am probably wrong in my implication but I am confused (nothing new there then :) ).

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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by Indigo_Sunrise » Wed Jun 22, 2011 3:48 pm

DavidLeodis wrote:In the explanation it states "the Moon's edge reflects a bluish tinge as well as it emerges from Earth's umbral shadow". That seems to me to imply that the Moon was appearing to move to the left, but when seen from the Earth it appears to move across to the right. I accept that I am probably wrong in my implication but I am confused (nothing new there then :) ).

Is it because the shadow is moving to the right, therefore the left side of the moon comes out of shadow first....?


Just a guess
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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by DavidLeodis » Wed Jun 22, 2011 5:02 pm

Indigo_Sunrise wrote:
DavidLeodis wrote:In the explanation it states "the Moon's edge reflects a bluish tinge as well as it emerges from Earth's umbral shadow". That seems to me to imply that the Moon was appearing to move to the left, but when seen from the Earth it appears to move across to the right. I accept that I am probably wrong in my implication but I am confused (nothing new there then :) ).

Is it because the shadow is moving to the right, therefore the left side of the moon comes out of shadow first....?


Just a guess
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Thanks Indigo_Sunrise. That is a good possibility. :)

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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by mexhunter » Thu Jun 23, 2011 12:40 pm

Hi Javier:

Although I did in another forum, I will not let the opportunity to congratulate you here too.
Beautiful picture!
Many greetings
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Re: APOD: Eclipsed Moonlight (2011 Jun 21)

Post by orin stepanek » Thu Jun 23, 2011 12:53 pm

Orin

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