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Friday, January 1, 2016

New Year's Aurora 2016-01-01


Click image to enlarge.

A recent solar storm produced a coronal mass ejection which is presently hitting the Earth's upper atmosphere, causing a brilliant auroral display in northern latitudes. Above is a picture I took a few minutes before midnight UTC on 2015-12-31 looking toward the north at latitude 54° North in the British Isles. You can see the southern part of the auroral oval around the geomagnetic pole. The green colour is due to atomic oxygen in the upper atmosphere excited by the energetic particles from the Sun. Toward the left you can see curtains descending from the main aurora which cut off sharply at an altitude of around 100 km where the abundance of atomic oxygen falls rapidly.

The photo above is a 30 second time exposure. The aurora, as observed with the dark-adapted unaided eye, is quite obvious in a dark sky but not as spectacular as in a long exposure photo. After your eye is dark-adapted you may be able to pick out the green colour, but you may see it only as grey.

The photo was taken with a Nikon D300 camera and Nikon 10.5 mm f/2.8 fisheye lens with ISO sensitivity 800. Exposure was 30 seconds at f/2.8. I post-processed the image with GIMP to stretch the contrast and remove the curvilinear distortion of the fisheye lens.

This is the first aurora I have ever seen.

Update: Here is a mouse-over animation demonstrating how the aurora changes rapidly over time. The two images were taken about a minute apart. Move the mouse over to show the second image and away to show the first. (2016-01-01 15:14 UTC)


Mouse-over to display image one minute later.

Posted at January 1, 2016 03:24