"Green + Red = Yellow" plus other color stories

The gamut of colors in this 120-second exposure are due to different physical phenomena:

(1) The blue in the clear sky close to the horizon is evening twilight;

(2) the yellow in the aurora is the combination of light from two different processes: (a) 5577 Å green light from energetic oxygen atoms decaying to a lower but still excited energy level, and (b) 6300 Å red light from less excited oxygen atoms decaying to their lowest energy level; finally,

(3) the purple blue at the top of the image comes from nitrogen molecular ions regaining an electron and emitting 4278 Å light, although there is probably a contribution from high-altitute red auroras combined with the blue evening twilight.

Nikon D810A + 16mm f/2.8D | Yellowknife, NT, Canada, 16 Sep 2015

Thanks to the Capital Suites Yellowknife hotel management for their generous support and to its staff for their friendly service.

© 2015 José Francisco Salgado, PhD.
Do not use without permission.
josefrancisco.org | Facebook | @jfsalgado

Taken in: Canada / Northwest Territories / Northwest Territories (show map)

Taken on: September 16, 2015

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16mm f/2.8D Fisheye

Canada

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full-frame fisheye

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Sets appears in: • Auroras • The Sky more » • CA: Yellowknife, NWT « less

Groups appears in: • FishEye • Aurora (Borealis and Australis) more » • fisheye fanatics • Nikkor 16mm 2.8 Fisheye • Aurora Borealis (Northern Lights) • Nikon D810A DSLR « less

Camera: Nikon D810A, f/4.5, 120 sec, 16mm, ISO 1000 (more info) (hide info)

Camera:	Nikon D810A
Lens:	16.0 mm f/2.8
Aperture:	f/4.5
Exposure Time:	120
Focal Length:	16mm
ISO:	1000
Exposure Bias:	0 EV
Flash:	Off, Did not fire
Exposure Program:	Manual
Exposure Mode:	Manual
Metering Mode:	Multi-segment
White Balance:	Auto
Gain Control:	High gain up
Saturation:	High
Sharpness:	Hard
Color Space:	sRGB
Software:	Adobe Photoshop CS6 (Macintosh)
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