Incredible all-sky picture

Incredible all-sky picture

Incredible all-sky picture

Bad Astronomy
The entire universe in blog form
Oct. 25 2010 7:00 AM

Incredible all-sky picture

The amazingly talented astrophotographer Stéphane Guisard has done it again! Check out this amazing 360° view of the entire sky:

guisard_fullsky

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

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[Click the picture to 2 π steradianate and get access to a zoomable, panable image.]

There's so much going on here it's hard to know where to start. Basically, Stéphane wanted to get the darkest sky possible for this shot. So he went to the Atacama desert in Chile, not far from the Paranal observatory. At that latitude, and at that time of year, the Milky Way -- usually seen as a band of light across the sky -- circles the horizon! That glow you see around the picture is not from cities or anything else like that, it's from the galaxy itself.

Since the Milky Way is so low in the sky, its soft light is minimized. He also took this picture at new Moon, so there was no light from that, either. Zodiacal light is sunlight reflected back to Earth from dust in the plane of the solar system, and he chose the time of the picture to minimize that as well.

The glow you can see in the picture is called gegenschein, and is sunlight reflected back to Earth from particles in the solar system, but this light is more concentrated in the area of the sky directly opposite the Sun's position. That's why it appears so bright in that oval, and fades away to the sides.

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What Stéphane has essentially achieved here is a picture with the darkest sky possible.

Pretty cool.

And the picture itself is filled with amazing sights! Here's an unwrapped version showing the entire horizon (this is on the page linked above in much higher res as well):

guisard_fullsky_unwrapped

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On the far left you can see the Large and Small Magellanic Clouds, satellite galaxies of our Milky Way. To the far right is the constellation of Orion, surrounded by the red glow of Barnard's Loop, a shell of hydrogen gas blown out by the hot, massive, luminous stars in Orion. You can also see the Andromeda Galaxy, and countless other objects too. He has an annotated version on that page which will help you find your way around.

Oh, and that brilliant star in the middle? That's no star, that's Jupiter. Please don't report it as a UFO.

This is an incredibly beautiful and clever image. I never would've though of something like this myself, but seeing the Milky Way wrapped around the horizon like that is an astonishing thing, even to an experienced skyhound like me. It just goes to show you that no matter how much time you spend enjoying the heavens, there's always more to see and new ways to see it.



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