APOD: Reflected Aurora Over Alaska (2013 Feb 12)

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APOD Robot
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APOD: Reflected Aurora Over Alaska (2013 Feb 12)

Post by APOD Robot » Tue Feb 12, 2013 5:06 am

Image Reflected Aurora Over Alaska

Explanation: Some auroras can only be seen with a camera. They are called subvisual and are too faint to be seen with the unaided eye. In the above image, the green aurora were easily visible to the eye, but the red aurora only became apparent after a 20-second camera exposure. The reason is that the human eye only accumulates light for a fraction of a second at a time, while a camera shutter can be left open much longer. When photographing an already picturesque scene near Anchorage, Alaska, USA, last autumn, a camera caught both the visual green and subvisual red aurora reflected in a lily pad-covered lake. High above, thousands of stars were visible including the Pleiades star cluster, while the planet Jupiter posed near the horizon, just above clouds, toward the image right. Auroras are caused by energetic particles from the Sun impacting the Earth's magnetosphere, causing electrons and protons to rain down near the Earth's poles and impact the air. Both red and green aurora are typically created by excited oxygen atoms, with red emission, when visible, dominating higher up. Auroras are known to have many shapes and colors.

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Moonlady
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Re: APOD: Reflected Aurora Over Alaska (2013 Feb 12)

Post by Moonlady » Tue Feb 12, 2013 6:30 am

A 'rainbow' aurora, beautiful ! :thumb_up:

horncastle

Re: APOD: Reflected Aurora Over Alaska (2013 Feb 12)

Post by horncastle » Tue Feb 12, 2013 12:03 pm

As an avid photographer, I have got to say this is perhaps the most stunning beautiful photo ever. It is true art. :)

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Chris Peterson
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Re: APOD: Reflected Aurora Over Alaska (2013 Feb 12)

Post by Chris Peterson » Tue Feb 12, 2013 3:11 pm

I've seen and imaged many auroras like this, and they are rarely called "subvisual". By far, the most common term for auroras like this is "photographic". The former term is better, but it just doesn't get used much.

In terms of perception, there are a few other interesting things at play here. Our eyes are much more sensitive to green light than to red, which is another reason that we are more likely to see the green components and miss the red. Also, our scotopic (black & white) vision is much more sensitive than our photopic (color) vision, so we actually see many of these photographic auroras, but we only see them as a gray glow, and seldom are able to distinguish them from the horizon glow present in most of our light polluted world. It is only when we make an image that the colors appear and let us separate the aurora from other sources. Even in this image, taken in what we might think of as the middle of nowhere, artificial light is seen to the east, about the same brightness as parts of the aurora.
Chris

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fausto.lubatti
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Re: APOD: Reflected Aurora Over Alaska (2013 Feb 12)

Post by fausto.lubatti » Tue Feb 12, 2013 3:23 pm

Magnificent colors and wonderful picture!

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Re: APOD: Reflected Aurora Over Alaska (2013 Feb 12)

Post by Boomer12k » Tue Feb 12, 2013 4:09 pm

Oooooooo, my oxygen is being excited!!!!

What a great picture!

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Re: APOD: Reflected Aurora Over Alaska (2013 Feb 12)

Post by MargaritaMc » Tue Feb 12, 2013 4:22 pm

So beautiful, so peaceful - but just imagine the ENERGY in that Aurora. More than all the power stations on Earth?
Margarita :shock:
"In those rare moments of total quiet with a dark sky, I again feel the awe that struck me as a child. The feeling is utterly overwhelming as my mind races out across the stars. I feel peaceful and serene."
&mdash; Dr Debra M. Elmegreen, Fellow of the AAAS

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Re: APOD: Reflected Aurora Over Alaska (2013 Feb 12)

Post by LocalColor » Tue Feb 12, 2013 4:41 pm

Very lovely photo. Thank you Todd Salat, your website is awesome.

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Ron-Astro Pharmacist
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Re: APOD: Reflected Aurora Over Alaska (2013 Feb 12)

Post by Ron-Astro Pharmacist » Tue Feb 12, 2013 4:51 pm

Interesting that the two spruces to the right of the picture seem to be lighted and the other brush around it not so much. Reflecting moon light or a photographic effect from processing the image :?: Dark skies and auroras - there are some benefits for being "off the beaten path" :ssmile: Nice, Nice picture!!!
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Re: APOD: Reflected Aurora Over Alaska (2013 Feb 12)

Post by Anthony Barreiro » Tue Feb 12, 2013 5:34 pm

This is a lovely picture! I'm planning a trip to see the northern lights for the first time this April, very exciting.

Thanks Chris for "scotopic" and "photopic", my new vocabulary words for today!

I appreciate the mouse-over star map. I have a hard time getting oriented to the sky in a photograph. In the real world once I've got my bearings I know the constellations well, but in a photo I don't have the same sense of direction and scale. In the unannotated picture I recognized the Pleiades, Hyades, Aldebaran, and Jupiter, but that was it. It's interesting to see how far Jupiter has retrograded since last fall. Once I saw the diagram, I could pick out M38, M36, and M37 in Auriga, pretty cool.
May all beings be happy, peaceful, and free.

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Re: APOD: Reflected Aurora Over Alaska (2013 Feb 12)

Post by Chris Peterson » Tue Feb 12, 2013 5:50 pm

Ron-Astro Pharmacist wrote:Interesting that the two spruces to the right of the picture seem to be lighted and the other brush around it not so much. Reflecting moon light or a photographic effect from processing the image :?: Dark skies and auroras - there are some benefits for being "off the beaten path" :ssmile: Nice, Nice picture!!!
There was no Moon. However, the photographer shone a flashlight around the pond to expose the lily pads, and I expect that also resulted in some illumination of the two trees close to the shore. Hard to say for sure, but they also look like they might be different species than the other trees- I'd say some sort of blue spruce, which would still be showing light colored growth tips early in autumn.
Chris

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Re: APOD: Reflected Aurora Over Alaska (2013 Feb 12)

Post by anon.a.mouse » Tue Feb 12, 2013 6:39 pm

Simply gorgeous. Maybe the most beautiful APOD I've ever seen.