Sunday, May 25, 2014

Airglow

The recent buzz of a possible great meteor shower Friday night / Saturday morning kept us all in anticipation of clear skies. It did not look good, but eastern Maine, specifically coastal Hancock County enjoyed clear skies all night long. The question was then whether the shower would pan out.

Early on I spotted what appeared to be a brilliant meteor exiting the constellation Camelopardalis. The night looked promising. The time since that 10 o'clock hour produced nary a trace of any members of the Camelopardalids. The night had a lack of meteors in general.

The dark and starry night still had gems to behold and one phenomena in general was putting on a decent show. Green colored airglow is the result of oxygen atoms roughly 60 miles high in the extreme upper atmosphere excited by ultraviolet radiation during the daytime.   The glow can be seen by astronauts in Earth's orbit and by stargazers with keen vision under dark skies.

Below is an example of green airglow and the Milky Way early Saturday morning as revealed by long exposure photography.

I noted it visually.  It appeared as large pale white patches of light against a darker sky. The camera sees the green light, but human eyes cannot detect color in such low light conditions as the rods, responsible for night vision do not detect color.

So dark skies are not always dark, indeed the whole front yard of my home seemed "bright".  My Sky Quality Meter read 21.6 Mags/Sq-Arc-sec, that's pretty dark.  The Milky Way was well structured and the dark nebulae in Ophiuchus were not a challenge at all.

These "bright nights" commonly occur during high solar activity, so visual and photographic observations in the coming Solar Minima will enjoy darker skies, a few years away, but it's not too early to start planning.


Airglow veils the Milky Way