Starship Asterisk*

by **geckzilla** » Sun Nov 08, 2015 8:38 am

It is blue, but it's a bit overexposed in that area, so that rim became white. Very simple answer. Look at this darkened version and you can see just on the fringes is some blue before it turns 100% white (saturated sensor). Anyway, there are probably conditions in which Rayleigh scattering sends more blue photons to the observer than other times. After all, we don't see blue skies at sunsets or rises.

by **alter-ego** » Sun Nov 08, 2015 5:48 am

Ann wrote:
alter-ego wrote:
Ann wrote:I'm still a bit confused at the utterly non-blue appearance of the Earth in today's APOD. Take a look at the picture at left, showing the Earth as seen from space. There is a prominent yellow-gray hurricane in the foreground, but the limb of the Earth is blue. There is absolutely no hint of blue in today's APOD.

Is the limb of the Earth typically blue when seen from space? During what circumstances is it not blue?

Finally, is it possible that the emission of more and more pollutants into the Earth's atmosphere could make it less blue when seen from space?

Ann
Sun has likely set - no blues. Earth must be fainter than the daytime views (and subsequently look washed-out) to achieve that image. However, it is possible that a 21% illuminated moon is illuminating the earth at this time.

Edit: At 21:27UT on Aug 9th the ISS was approaching sunrise in a few minutes. If I interpreted the view direction to the Milky Way correctly, the sun would rise within, or close to, the camera FoV.
Thanks, and good point, alter-ego, but the moonlit Earth sky is actually blue, as can be seen in this picture by Dario Giannobile. David Malin, the British-Australian astrophotographer, specifically pointed out in his book A View of the Universe that the moonlit sky is blue. So it seems to me that if the Earth is illuminated by the Moon, even if it is only a 21% Moon, that should not preclude the limb of the Earth from looking blue.

Could it be that the Sun has set, there is negligible moonlight, and the cloud cover of the Earth is "lit from within", by light pollution? Would that make the limb of the Earth look non-blue?

You pointed out that sunrise is fast approaching in this image. Could the reddish tones of the atmosphere at right be the red sky of dawn?

I'm not convinced that the lighting and conditions are good enough to pull out the blue you want to see. There very may be blue photons but maybe they are not effectively capture here. (I've not analyzed the image to know what degree blue is or is not present) The APOD view is a unique one and your examples aren't good ones to replicate the APOD case - even clouds complicate this. But the brighter & reddish glow could indicate sunrise is not far away.

Edit: I'd like to see an appropriately exposed, nighttime ISS image showing moon-lit clouds (& sky) with the moon behind the camera.

by **Ann** » Sun Nov 08, 2015 5:22 am

alter-ego wrote:
Ann wrote:I'm still a bit confused at the utterly non-blue appearance of the Earth in today's APOD. Take a look at the picture at left, showing the Earth as seen from space. There is a prominent yellow-gray hurricane in the foreground, but the limb of the Earth is blue. There is absolutely no hint of blue in today's APOD.

Is the limb of the Earth typically blue when seen from space? During what circumstances is it not blue?

Finally, is it possible that the emission of more and more pollutants into the Earth's atmosphere could make it less blue when seen from space?

Ann
Sun has likely set - no blues. Earth must be fainter than the daytime views (and subsequently look washed-out) to achieve that image. However, it is possible that a 21% illuminated moon is illuminating the earth at this time.

Edit: At 21:27UT on Aug 9th the ISS was approaching sunrise in a few minutes. If I interpreted the view direction to the Milky Way correctly, the sun would rise within, or close to, the camera FoV.

Thanks, and good point, alter-ego, but the moonlit Earth sky is actually blue, as can be seen in this picture by Dario Giannobile. David Malin, the British-Australian astrophotographer, specifically pointed out in his book A View of the Universe that the moonlit sky is blue. So it seems to me that if the Earth is illuminated by the Moon, even if it is only a 21% Moon, that should not preclude the limb of the Earth from looking blue.

Could it be that the Sun has set, there is negligible moonlight, and the cloud cover of the Earth is "lit from within", by light pollution? Would that make the limb of the Earth look non-blue?

You pointed out that sunrise is fast approaching in this image. Could the reddish tones of the atmosphere at right be the red sky of dawn?

Ann

by **alter-ego** » Sun Nov 08, 2015 4:29 am

Ann wrote:I'm still a bit confused at the utterly non-blue appearance of the Earth in today's APOD. Take a look at the picture at left, showing the Earth as seen from space. There is a prominent yellow-gray hurricane in the foreground, but the limb of the Earth is blue. There is absolutely no hint of blue in today's APOD.

Is the limb of the Earth typically blue when seen from space? During what circumstances is it not blue?

Finally, is it possible that the emission of more and more pollutants into the Earth's atmosphere could make it less blue when seen from space?

Ann

Sun has likely set - no blues. Earth must be fainter than the daytime views (and subsequently look washed-out) to achieve that image. However, it is possible that a 21% illuminated moon is illuminating the earth at this time.

Edit: At 21:27UT on Aug 9th the ISS was approaching sunrise in a few minutes. If I interpreted the view direction to the Milky Way correctly, the sun would rise within, or close to, the camera FoV.
... and yes the moon was visible from the ISS at this time at rough 35° altitude and almost 180° directly behind the camera.

by **Ann** » Sun Nov 08, 2015 4:06 am

: Click to view full size image

I'm still a bit confused at the utterly non-blue appearance of the Earth in today's APOD. Take a look at the picture at left, showing the Earth as seen from space. There is a prominent yellow-gray hurricane in the foreground, but the limb of the Earth is blue. There is absolutely no hint of blue in today's APOD.

Is the limb of the Earth typically blue when seen from space? During what circumstances is it not blue?

Finally, is it possible that the emission of more and more pollutants into the Earth's atmosphere could make it less blue when seen from space?

Ann

by **Ann** » Sun Nov 08, 2015 3:48 am

heehaw wrote:
BTW, it was first described by Ångström, which you should find interesting.
Without him, Å would not be on my keyboard I'm sure! No idea what the pronunciation difference is between A and Å. Uh?

Ångström was a Swedish scientist, and the letter "Å" was originally invented by Swedes, or so I think anyway. The little ring above the "A" is supposed to say that this is the letter A when it's pronounced they way most of you Europeans pronounce the letter O. But in English "A" and "O" are not pronounced like they are pronounced in most West European languages, so let me explain.

In English, the vowel sound in "arm" resembles the Swedish letter "A". The vowel sound in "ought" resembles the Swedish "Å". But those are the "long" pronunciations of "A" and "Å". A short Swedish "A" is pronounced much like the vowel sound in "cut". A short "Å" is pronounced much like the vowel sound in "not".

The vowel in "Ångström" is short. The "ö" (which is quite different from "o") is also short, and it sounds a bit - a bit like the vowel sound of "Earth". But it is shorter.

Want to know how to say Ångström in Swedish? You can listen to it here. Press the arrow in front of the words "Uttal av KristinaEkstrand".

Ann

by **heehaw** » Sun Nov 08, 2015 12:03 am

BTW, it was first described by Ångström, which you should find interesting.

Without him, Å would not be on my keyboard I'm sure! No idea what the pronunciation difference is between A and Å. Uh?

by **Markus Schwarz** » Sat Nov 07, 2015 5:51 pm

isoparix wrote:From inside the ISS I assume? Any cameras mounted outside?

There are a few and you can watch the live stream here.

by **Chris Peterson** » Sat Nov 07, 2015 4:44 pm

Ann wrote:
Chris Peterson wrote:Well, clouds are pretty neutral colored, which means they look gray if they're not exposed to saturation. And the airglow is probably over 100 km high, while the visible atmosphere only extends to 20 or 30 km (if that).
Thanks, Chris. What causes the airglow?

Mostly, it is luminescence- atoms which have absorbed energy from sunlight (and typically combine with other atoms to form molecules), and then release that energy slowly over time in the form of light. It is usually green, but there are rarer reactions that produce other colors, including red.

BTW, it was first described by Ångström, which you should find interesting.

by **Ann** » Sat Nov 07, 2015 4:09 pm

Chris Peterson wrote:
Ann wrote:The Earth looks gray and yellow in this image, and then a red band is floating along the limb of the Earth, clearly separated from the visible disk and even from the visible atmosphere of the Earth.
Well, clouds are pretty neutral colored, which means they look gray if they're not exposed to saturation. And the airglow is probably over 100 km high, while the visible atmosphere only extends to 20 or 30 km (if that).

Thanks, Chris. What causes the airglow?

Ann

by **Chris Peterson** » Sat Nov 07, 2015 3:49 pm

Ann wrote:The Earth looks gray and yellow in this image, and then a red band is floating along the limb of the Earth, clearly separated from the visible disk and even from the visible atmosphere of the Earth.

Well, clouds are pretty neutral colored, which means they look gray if they're not exposed to saturation. And the airglow is probably over 100 km high, while the visible atmosphere only extends to 20 or 30 km (if that).

by **Chris Peterson** » Sat Nov 07, 2015 3:43 pm

Stewart Coulter wrote:Wow - that sort of clarity and detail in just 5s from space. Remarkable!

I would like to know what a space walker sees of the stars and milky way with their eyes in the day.

The view of the sky is only a little better from space than from a dark site on Earth. Most people probably wouldn't notice the difference. For a spacewalker, the attenuation through the glass of his helmet would probably be greater than through Earth's atmosphere, meaning you'd have a better view from the ground. And you could get an equivalent image of the Milky Way from the ground using the same camera settings.

by **kensuess** » Sat Nov 07, 2015 2:32 pm

aildoux wrote:Great to see stars through Earth's atmosphere. Also love the combination of our galaxy with our planet.

I would not expect that stars would be visible through that much atmosphere.

by **tomatoherd** » Sat Nov 07, 2015 2:11 pm

since the earth and station are both in shadow, I presume the sun is on the far side of the earth, perhaps not far above the inverted horizon. So what I like about this image is that it puts both our planet and star squarely (should say flatly) in the plane of the galactic disc objectively, and not just inferred by being 'the observer'. We see 'us' in the disc. Best part of it, to me....

by **isoparix** » Sat Nov 07, 2015 11:17 am

From inside the ISS I assume? Any cameras mounted outside?

by **Stewart Coulter** » Sat Nov 07, 2015 9:45 am

Hang on - what sort of exposure was that? The station rotates 360* every 90 min: 15s per * Now there's only a slight smudge in the stellar images which indicate a fraction of a second....

...just followed the "snapshot from space" link and I see it was 5s at f/1.4 and ISO 8000 so 20 minutes of arc smudge. 24.3mm focal length so 73* x 53* field of view. Now since smudge is vertical it should be about 1/160 th of the height which on my screen is 120mm and - yes - the smudge IS about 1mm!

So from thinking this is a composite I see it is not. Wow - that sort of clarity and detail in just 5s from space. Remarkable!

I would like to know what a space walker sees of the stars and milky way with their eyes in the day.

by **aildoux** » Sat Nov 07, 2015 6:21 am

Great to see stars through Earth's atmosphere. Also love the combination of our galaxy with our planet.

by **Ann** » Sat Nov 07, 2015 6:08 am

The Earth looks gray and yellow in this image, and then a red band is floating along the limb of the Earth, clearly separated from the visible disk and even from the visible atmosphere of the Earth.

To me the Earth looks strange here.

Ann

by **APOD Robot** » Sat Nov 07, 2015 5:10 am

Earth and Milky Way from Space

Explanation: Since November 2000, people have been living continuously on the International Space Station. To celebrate humanity's 15th anniversary off planet Earth, consider this snapshot from space of our galaxy and our home world posing together beyond the orbital outpost. The Milky Way stretches below the curve of Earth's limb in the scene that also records a faint red, extended airglow. The galaxy's central bulge appears with starfields cut by dark rifts of obscuring interstellar dust. The picture was taken by Astronaut Scott Kelly on August 9, 2015, the 135th day of his one-year mission in space.

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