Thursday, June 21, 2012

Airglow, Not Aurora!

Last night's post evidently stimulated some interest, but some were perhaps mislead from my title of the post, "Arizona Aurora?".  At the time I observed it, the northern location of the brightest sections, and the pinkish color seen in some images had me thinking it might have been aurora.  In addition, there were auroral displays seen as far south as Northern Utah on Saturday night, 16 June, the night AFTER my first observation.

So what I saw and the photos posted are airglow - the brightest airglow displays I've ever seen!.  While resembling the greenish color of aurora, and occupying nearly the same part of our atmosphere at about 90km altitude, they are different phenomenon.  Aurora are caused by energetic particles spiraling down the earth's magnetic field, while airglow is caused by excitation of atoms in the upper atmosphere by daytime solar UV radiation.

There is an excellent site on atmospheric optics called "Optics Picture of the Day".  They maintain a gallery on a wide range of optical effects, including the above topics, with very well-written explanations of what the images illustrate.  My favorite image of airglow from the site is from an all-sky image at local midnight from Nebraska a half-dozen years ago.  There are also examples of similar banded airglow to my image and an image from space showing airglow from above.  They also have several examples and explanations of gravity waves.  I highly recommend bookmarking the site and returning frequently to learn about many of the sights we can see in the sky, both day and night.

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