APOD: ALMA Milky Way (2014 Jul 24)

Comments and questions about the APOD on the main view screen.
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APOD: ALMA Milky Way (2014 Jul 24)

Post by APOD Robot » Thu Jul 24, 2014 4:08 am

Image ALMA Milky Way

Explanation: This alluring all-skyscape was taken 5,100 meters above sea level, from the Chajnantor Plateau in the Chilean Andes. Viewed through the site's rarefied atmosphere at about 50% sea level pressure, the gorgeous Milky Way stretches through the scene. Its cosmic rifts of dust, stars, and nebulae are joined by Venus, a brilliant morning star immersed in a strong band of predawn Zodiacal light. Still not completely dark even at this high altitude, the night sky's greenish cast is due to airglow emission from oxygen atoms. Around the horizon the dish antenna units of the Atacama Large Millimeter/submillimeter Array, ALMA, explore the universe at wavelengths over 1,000 times longer than visible light.

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Re: APOD: ALMA Milky Way (2014 Jul 24)

Post by geckzilla » Thu Jul 24, 2014 4:37 am

My forward-facing primate eyes are confused by the all-skyscape. Most of the dishes are pointing at the same spot but some aren't. I can't seem to pick out exactly which ones are and which ones are not.
Just call me "geck" because "zilla" is like a last name.

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Re: APOD: ALMA Milky Way (2014 Jul 24)

Post by Chris Peterson » Thu Jul 24, 2014 4:49 am

There is the implication that this image owes much to the altitude of the site. But the sky would look identical to a camera at sea level, assuming dark, dry skies. And almost identical visually, as well. The altitude has very little effect on the limiting magnitude.

What is important for submillimeter astronomy is the absence of water, and that is very low indeed, because of both the regional topography and the altitude.
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Re: APOD: ALMA Milky Way (2014 Jul 24)

Post by Markus Schwarz » Thu Jul 24, 2014 8:22 am

Chris Peterson wrote:There is the implication that this image owes much to the altitude of the site. But the sky would look identical to a camera at sea level, assuming dark, dry skies. And almost identical visually, as well. The altitude has very little effect on the limiting magnitude.

What is important for submillimeter astronomy is the absence of water, and that is very low indeed, because of both the regional topography and the altitude.
Thanks Chris, I have been wondering myself. Maybe they mean latitude? If you want dark skies, I guess being in the southern hemisphere at large latitude helps at this time of year.

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Re: APOD: ALMA Milky Way (2014 Jul 24)

Post by MalcolmPark » Thu Jul 24, 2014 4:25 pm

There is also the implication that this image was shot last night but based on the location of Venus my guess is it was shot in April.

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Re: APOD: ALMA Milky Way (2014 Jul 24)

Post by Chris Peterson » Thu Jul 24, 2014 5:08 pm

Markus Schwarz wrote:Thanks Chris, I have been wondering myself. Maybe they mean latitude? If you want dark skies, I guess being in the southern hemisphere at large latitude helps at this time of year.
I think they meant altitude. High altitude locations are associated with dark clarity, it's just that the reason has much more to do with remoteness than altitude.

There are sites as dark as this all over the world, and not all are terribly remote or hard to reach.
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Re: APOD: ALMA Milky Way (2014 Jul 24)

Post by ta152h0 » Thu Jul 24, 2014 7:18 pm

and I thought high altitudes were also associated with lack of distortion from the thicker atmosphere ?
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Re: APOD: ALMA Milky Way (2014 Jul 24)

Post by MalcolmPark » Thu Jul 24, 2014 7:21 pm

maybe thats a benefit at longer focal lengths, but theres not much difference with an 8mm fisheye which is what this looks like