by APOD Robot » Tue Feb 12, 2013 5:06 am
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.
[/b]
[url=http://apod.nasa.gov/apod/ap130212.html][img]http://apod.nasa.gov/apod/calendar/S_130212.jpg[/img] [size=150]Reflected Aurora Over Alaska[/size][/url]
[b] Explanation: [/b] Some [url=http://odin.gi.alaska.edu/FAQ/]auroras[/url] can only be seen with a camera. They are called [url=http://en.wiktionary.org/wiki/subvisual]subvisual[/url] and are too faint to be seen with the unaided eye. In the [url=http://www.aurorahunter.com/lily-red.php]above image[/url], 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 [url=http://en.wikipedia.org/wiki/Human_eye]human eye[/url] 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 [url=http://en.wikipedia.org/wiki/Anchorage]Anchorage[/url], [url=http://en.wikipedia.org/wiki/Alaska]Alaska[/url], [url=http://en.wikipedia.org/wiki/United_States]USA[/url], 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 [url=http://apod.nasa.gov/apod/ap120903.html]Pleiades[/url] star cluster, while the planet Jupiter posed near the horizon, just above clouds, toward the image right. [url=http://en.wikipedia.org/wiki/Aurora_%28astronomy%29]Auroras[/url] are caused by [url=http://apod.nasa.gov/apod/ap031029.html]energetic particles[/url] from the [url=http://apod.nasa.gov/apod/sun.html]Sun[/url] impacting the Earth's [url=http://en.wikipedia.org/wiki/Magnetosphere]magnetosphere[/url], causing [url=http://www-istp.gsfc.nasa.gov/Education/welect.html]electrons[/url] and [url=http://hyperphysics.phy-astr.gsu.edu/hbase/particles/proton.html]protons[/url] to rain down near the Earth's poles and impact the air. Both red and green aurora are [url=http://www.atoptics.co.uk/highsky/auror3.htm]typically created[/url] by excited [url=http://periodic.lanl.gov/8.shtml]oxygen[/url] atoms, with red emission, when visible, dominating higher up. [url=http://apod.nasa.gov/apod/%20https://www.google.com/search?hl=en&safe=off&authuser=0&site=imghp&tbm=isch&source=hp&biw=1106&bih=732&q=site%3Aapod.nasa.gov+aurora&oq=site%3Aapod.nasa.gov+aurora&gs_l=img.3...1569.4955.0.6435.25.6.0.19.0.0.127.551.4j2.6.0...0.0...1ac.1.2.img.AHUAaS3haQ0]Auroras[/url] are known to have many [url=http://apod.nasa.gov/apod/ap051120.html]shapes[/url] and [url=http://apod.nasa.gov/apod/ap040730.html]colors[/url].
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