APOD: Orion Arising (2014 Jun 28)

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APOD: Orion Arising (2014 Jun 28)

Post by APOD Robot » Sat Jun 28, 2014 4:10 am

Image Orion Arising

Explanation: Orion's belt runs just along the horizon, seen through Earth's atmosphere and rising in this starry snapshot from low Earth orbit on board the International Space Station. The belt stars, Alnitak, Alnilam, and Mintaka run right to left and Orion's sword, home to the great Orion Nebula, hangs above his belt, an orientation unfamiliar to denizens of the planet's northern hemisphere. That puts bright star Rigel, at the foot of Orion, still higher above Orion's belt. Of course the brightest celestial beacon in the frame is Sirius, alpha star of the constellation Canis Major. The station's Destiny Laboratory module is in the foreground at the top right.

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Re: APOD: Orion Arising (2014 Jun 28)

Post by saturno2 » Sat Jun 28, 2014 5:37 am

Very very interesting

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Ann
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Re: APOD: Orion Arising (2014 Jun 28)

Post by Ann » Sat Jun 28, 2014 5:38 am

How interesting!

The Earth's atmosphere looks strangely reddish, with a thin layer of greenish-blue on top.

It seems to me that the belt stars, which are seen through the atmosphere, should look reddened. No such effect can be seen. though. How fascinating it would be to have some fast and super-sensitive photometric equipment on board, which could measure the B-V of the belt stars when they are seen through the atmosphere, and then repeat the measurement when the atmosphere is no longer in front of the stars. What would the difference be, if any? Oh, there really should be some difference, I think.

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Re: APOD: Orion Arising (2014 Jun 28)

Post by b92541 » Sat Jun 28, 2014 1:29 pm

I always wished that there were more real views of the stars from space. Thought there should be a web accessible camera pointing out to space instead of toward earth.

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Re: APOD: Orion Arising (2014 Jun 28)

Post by NGC3314 » Sat Jun 28, 2014 8:26 pm

Ann wrote:How interesting!
The Earth's atmosphere looks strangely reddish, with a thin layer of greenish-blue on top.
In this nocturnal grazing view, we're seeing the airglow layers of O and Na excited by (IIRC) collisions with molecules (OH glows pretty fiercely at longer wavelengths; these are all sworn enemies of ground-based astronomers). The sodium airglow comes from a layer something like 100 km up, and oxygen (at 5577/6300/63636 Angstroms) higher yet, so we can see those from altitudes where there is not enough reddening to be noticeable.

Looking at some videos and stills of moonrise and moonset from ISS, it's striking how close the line of sight has to come to the surface to see reddening, much less obvious than refraction. It must mostly happen not just in the troposphere but the lowest few km of the troposphere.

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Re: APOD: Orion Arising (2014 Jun 28)

Post by Boomer12k » Sat Jun 28, 2014 10:18 pm

AWESOME!!!!!

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Re: APOD: Orion Arising (2014 Jun 28)

Post by Boomer12k » Sat Jun 28, 2014 10:23 pm

It is interesting that there is less..."SHEEN" in the atmosphere at the location of the Belt stars...and it is "bluer" there too....


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Re: APOD: Orion Arising (2014 Jun 28)

Post by DavidLeodis » Sun Jun 29, 2014 11:23 am

Great photo. :)

Nice also that it was taken by Reid Wiseman (a member of Expedition 40 for those who have not checked the links) rather than being copied from elsewhere and then submitted by someone else.

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Re: APOD: Orion Arising (2014 Jun 28)

Post by Leadcommander » Sun Jun 29, 2014 10:18 pm

Lovely photo, strange though that the orion stars are infront of the planet as with a lot of other stars
Photo must be a combination of photos to get this lovely photo

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Re: APOD: Orion Arising (2014 Jun 28)

Post by Chris Peterson » Sun Jun 29, 2014 11:49 pm

Ann wrote:It seems to me that the belt stars, which are seen through the atmosphere, should look reddened. No such effect can be seen. though.
Just for kicks I did a few calculations. Given that the horizon is 2351 km from the ISS, and looking at the angular scale provided by the known stars, this image shows the belt stars shining through atmosphere that is a minimum of 29 km above sea level. Atmospheric density at that height is only 1.6% of what it is at sea level, and most of the atmospheric optical path is through much lower densities than that. Integrate that path and you have less than one standard air mass. In other words, the reddening we see here from Rayleigh scattering is actually less than you get looking at stars straight overhead from sea level.
Chris

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Re: APOD: Orion Arising (2014 Jun 28)

Post by Nitpicker » Mon Jun 30, 2014 2:42 am

Chris Peterson wrote:Just for kicks I did a few calculations. Given that the horizon is 2351 km from the ISS, and looking at the angular scale provided by the known stars, this image shows the belt stars shining through atmosphere that is a minimum of 29 km above sea level. Atmospheric density at that height is only 1.6% of what it is at sea level, and most of the atmospheric optical path is through much lower densities than that. Integrate that path and you have less than one standard air mass. In other words, the reddening we see here from Rayleigh scattering is actually less than you get looking at stars straight overhead from sea level.
Now that is interesting. Thanks Chris.

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Re: APOD: Orion Arising (2014 Jun 28)

Post by neufer » Mon Jun 30, 2014 9:48 am

Chris Peterson wrote:
Just for kicks I did a few calculations. Given that the horizon is 2351 km from the ISS, and looking at the angular scale provided by the known stars, this image shows the belt stars shining through atmosphere that is a minimum of 29 km above sea level. Atmospheric density at that height is only 1.6% of what it is at sea level, and most of the atmospheric optical path is through much lower densities than that. Integrate that path and you have less than one standard air mass. In other words, the reddening we see here from Rayleigh scattering is actually less than you get looking at stars straight overhead from sea level.
http://www.albany.edu/faculty/rgk/atm101/airglow.htm wrote:
The brightest region of airglow is ... at an altitude of about 100 km (i.e., the Kármán line).
It's a little hard to judge exactly where the Earth's horizon starts but I would guess that the belt stars are at least half way up to the airglow Kármán line (~ 2º angular thickness from ISS vs. ~ 3º width of Orion's Belt) ... making for a minimum altitude of 50 km above sea level.

Atmospheric density at that height is only 0.1% of what it is at sea level. So the reddening we see here from Rayleigh scattering is actually less than 7% of what one gets looking at stars straight overhead from sea level.
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