(meteorobs) re Astro versus Nautical Twilight

[BRUCE MCCURDY]

Here at 54° N. (Edmonton, Alberta, Canada), perpetual twilight persists from mid-May to the beginning of August. Eleven long weeks. Fortunately I'm an observer of both the Sun and noctilucent clouds which are both going great guns during those weeks. but the nights are both short and bright.The SDAs come just towards the end of that but are a pretty poor shower for us. The Perseids effectively mark the return of dark sky observing season.Bruce*****-----Original Message-----From: wisetdf at Safe-mail.netTo: meteorobs at meteorobs.orgSent: 05/08/2011 02:07 PMSubject: RE: (meteorobs) re Astro versus Nautical Twilight
 On double checking things it looks like I got my Astronomical and Nautical twilights mixed up.  Sorry about that.

I've no idea about Nautical Twilight, but again in the Summer months at just above mid Northern latitudes the sky is notably less dark during the duration when it is only _Astronomical_ Twilight all night long.  I'm seeming to remember Airglow is a bigger problem in Summer months than Winter ones too.  Looking into that on the web that might be because Airglow seems to have a bit of remnant Dayglow, a lot of Twilightglow and as well some of the usual Nightglow all going on :- http://www.albany.edu/faculty/rgk/atm101/airglow.htm .  In Northern Summer when facing South you've extra starglow because you're facing the Galactic Centre.  All these little bits probably add up, though at Nautical Twilight those are probably fainter than the seeing limit.

The buzzing mosquitoes don't help much either.

You sometimes have to wonder how Scandinavian astronomers manage to do all the work they've done over the years, what with all night twilights and noctilucent clouds all Summer, and bright Aurorae for long parts of Winter, they must have very narrow observing seasons available to them!

Cheers

John
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