[AZ-Observing] Re: Southern Milkyway with Sigma fisheye
- From: Brian Skiff <bas@xxxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Mon, 15 Sep 2008 11:27:58 -0700
> The sky was fairly dark in the Outback, reading 21.6 on the SQM
> meter in a bland part of the sky.
>
> Since there was no source of light pollution down to the horizon,
> I wonder why the reading wasn't closer to 22.0. Was the reading
> affected by the presence of the Milky Way. I thought that people
> have read 21.6 from their SQM's at Five Mile Meadow, which is dark,
> but it ain't the Outback.
I guess I'm inferring that Chris waited until much later in
the night to make the SQM reading, so the the south galactic pole
was more nearly overhead. Assuming he's using one of the regular
wide-field SQMs, the 21.6 mag/square arcsec figure is about what
folks are getting at remote sites generally at "average" sidereal
times. With the Cygnus Milky Way on the meridian in the past
month, I've been getting 21.5 - 21.6 from Anderson Mesa. Remember
the values will be affected a lot also by geomagnetic activity
and by aerosols (making a bright site brighter, but a dark site
darker), so interpreting the SQM readings is not straightforward
without a good series at the same site (data over many months).
There's lots of "astrophysics" displayed in Chris' image.
Just a couple of things that caught my eye: Grus near the upper-left
edge (looks like a Greek letter lambda turned over to the right),
which is on the meridian in Arizona these days before midnight;
the zodiacal light and band extending from bottom to top across
the entire image; the pervasive strong reddening of the Milky Way
near the galactic center and for either side for 30-40 degrees;
the near-symmetry of the Scutum and Norma starclouds, with the
Scutum cloud a bit more concentrated/brighter but also more reddened;
the broad vast dark cloud extending from the Ophiuchus region
(which is already familiar) across the Milky Way (nearly vertically
in the picture) to the patchy extension south of Aquila (left of
Altair in the photo), which I'd never noticed before either
visually or on photos; the general blueness of the Cygnus starcloud
on the far upper-right matched (again semi-symmetrically) by the
blueness of the Carina-Crux-Centaurus region flanking the Crux
Coalsack---you have to say "Crux Coalsack" since there are also
the Carina and Centaurus coalsacks on either side of it, which are
nearly as prominent visually. Anyway, both regions are dominated
by B- and A-type stars around 9th to 12th magnitude, which are
the stars that produce the visual impression of the Milky Way.
And of course the Emu coming out from alpha Centauri, upside-down
in this picture. ...plus lots more of the obvious stuff you're
already familiar with (right?).
\Brian
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