(IAAC) Seeing in New England isn't THAT bad!
The following message appeared on the 'amastro' Pro-Am observing list
this weekend. It's from Brian Skiff, well-known pro-am astronomer and
co-author of the "Observing Handbook": apparently, atmospheric seeing
in New England is not as bad relatively speaking as we may complain it
is? Of course, 3" seeing is nothing to celebrate over either. :)
------------------------------ message 1529 ------------------------------
Date: Sun, 23 Jan 2000 17:50:23 -0700 (MST)
From: Brian Skiff <firstname.lastname@example.org>
Subject: [amastro] Seeing quality around the world
Recently Arne Henden (USNO-Flagstaff) has been collection CCD frames of
a photometric standard region in M67 from (mostly amateur) asteroid
astrometrists via the 'mpml' mailing list. The idea was to reduce the frames,
which are all unfiltered, in a standard way to see what the actual color terms
were for various "real world" CCDs when used in this way. A serious problem
has developed in the last several years with asteroid magnitudes as a result
of most observers using software that produces differential magnitudes with
respect to either the GSC or USNO-A star catalogues. Neither catalogue
contains magnitudes on any standard system, and the zero-point varies
considerably from field to field across the sky. As a result, the collection
of magnitudes for asteroids has been totally corrupted, particularly for
fainter objects and recent discoveries (which is perhaps three-quarters of the
known objects in both senses).
Well, besides highlighting the great variation in the reported magnitudes,
the reductions Henden did also include notes about the image scale and the
size of the star images. The results were perhaps surprising: even the best
site had rather poor seeing. The list is shown below. The first column shows
the observer last-name, followed by the full-width-half-maximum size of the
stars on the frame delivered to Henden. The image scale is in arcseconds per
pixel; in four cases marked with an asterisk the pixels are big enough that the
stars are undersampled and thus the fwhm is not a reliable estimate of the
seeing. Locations are shown as I could determine them.
To be fair, the seeing fwhm sizes include errors in focus, tracking,
and crummy optics (most folks operate with some sort of focal-reducer, which
does nothing to make images better). The worst seeing shown was obtained
when the field was only 30 degrees above the horizon, so that is also not a
fair estimate. Nevertheless, the implication is that the typical "backyard"
observatory has pretty bad seeing. Median seeing at Lowell's Anderson Mesa
site is 1".2, and I consider it too soft for deep-sky viewing if it's over
1".5. Guess I should stop complaining.
observer fwhm(") scale("/pxl) Location
Bayus 5.6 1.60 Flint MI
Busch 7.0 2.51 Heppenheim FRG
diCicco 2.9 1.02 Sudbury MA
Frey 6.2 3.43* Meyer AZ
Garradd 4.7 2.03 Loomberah NSW
Klinglesmith 3.3 3.72* Socorro NM
Nicolini 4.9 2.14 Italy
Owen 2.1 0.33 Table Mtn CA
Roe 5.7 2.12 Oaxaca MX
Sheldrick 5.4 2.44 ??
Sposetti 5.5 2.39 northern Italy
Starkey 3.8 3.15* ??
Sullivan 9.5 2.31 CA? (sec z=2.0)
Waller 3.2 2.02* Ada OK
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