[AZ-Observing] Re: az-observing Digest V14 #150
- From: Robert Ayers <astroayers@xxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Thu, 19 Jun 2014 10:29:34 -0700
On Wed, Jun 18, 2014 at 10:13 PM, Paul Lind wrote:
> While observing at Ash Fork during the last DOTM we noticed that the
> evening twilight crept slowly northward, reaching a point almost below
> Polaris. This was long after the end of astronomical twilight, which was
> listed as about 9:20 pm. The phenomenon is logical since the sun was
> only about 30 degrees below the horizon in the north at its very lowest.
> I'd never noticed this before in my hundreds of years of observing. (Well
> maybe not hundreds). It's definitely interesting and worth looking for this
> time of year, requiring only a dark site and no light domes in the NW.
>
I noticed the exact same thing a year ago (June 9 2013). I actually emailed
Brian Skiff and asked "was there a weak aurora last night?"
Brian pointed out that it was near the solstice and that the sun didn't
sink that low. The "extended twilight" was obvious circa 10:30 MST, but
did not, for me, last all night. My notes say "At midnight MST I suspect
that the sky in the north is a bit brighter than a twilight free horizon,
but it is not obvious like the NW is at 10:30". (My northern horizon is a
bit elevated, which complicates this observation.)
(I note that 10:30 MST in Ash Fork is only about 10pm local time, cause the
MST timezone is shifted west -- the centerline for timezone -7 should be
longitude 105, which is over by Albuquerque.)
Bob Ayers
*www.RobertMartinAyers.org <http://www.RobertMartinAyers.org> *
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