[sac-forum] Call for Observations
- From: "AJ Crayon" <acrayon@xxxxxxx>
- To: "SAC Forum" <sac-forum@xxxxxxxxxxxxx>
- Date: Fri, 26 Dec 2008 21:00:11 -0700
So far I've got observations for the Trumpler study from Dan Gruber and Dick
Harshaw. It isn't to late to get yours in. So for those hearty souls that are
intending to brave the clear, cold skies for Saturday here is two months worth
of observing.
For January we will do something a little different, like do a study of
Trumpler classification for open clusters. Briefly there are 3 codes used to
describe a cluster. They are concentration, magnitude range and richness. The
first, concentration, indicates how the cluster stands out from the Milky Way
background and used 4 Roman Numerals. Their descriptions are
I Detached, strong concentration towards the center,
II Detached, weak concentration towards the center,
III Detached, no concentration towards the center,
IV Not well detached from surrounding star field.
There are 3 number for magnitude range; 1 for small or ±2 magnitudes, to 3 for
wide range. One of 3 letters are used for richness they are p for poor, under
50 stars; m for medium with 50 to 100 stars and r for rich, over 100 stars.
For this session we will have all concentration classes as they seem to be the
description causing the most difficulty. To this end we will not stay in one
constellation as in the past, but will meander around fall constellations. If
you are interested in learning more about this classification methodology see
Touring the Trumpler Classes by Richard Harshaw, which can be found on the SAC
web site. To get a better feel for the classification, pan around the cluster
to see how the detached description relates to each. While at it note the
magnitude range and count, or estimate, the number of stars. Now on to the
clusters, in descending concentration order. M 37 in Auriga is I 2r. IC 361
in Camelopardalis is II 1 r. NGC1513 in Perseus is II 1 m. NGC7789 in
Cassiopeia is II 2 r. Back into Perseus for III 1 r is NGC1245. Finally,
again in Cassiopeia is NGC 225 an III 1 p cluster. Now, having done this
study, perhaps we should consider doing during the summer. Let me know your
thoughts and preferences.
It just seems there is more and more left to do in Cassiopeia, so let's not
delay any more. While there are a few galaxies we will steer clear of them, at
least until the spring. For this pass we will do, mostly, open clusters and,
oh, don't forget to review the Trumpler Class for each. With that the first is
NGC7788, containing about 20 stars from 10th mag. It is just northwest of
NGC7790, don't confuse them. Moving east about 4° is a Herschel 400, NGC 136
that is much smaller and fainter. King 16 is to the northeast and may be a
little harder to detect than the previous cluster. Moving another 6.6° east is
our next, NGC 637 another Herschel 400 entry. It is also pretty small but
should stand out from the Milky Way background. Advancing much farther east is
NGC1027, last of the Herschel 400 entries for this month. It is rather large,
has about 40 stars from mag 9.3; but this depends on where the cluster boundary
is determined. Our last is an asterism titled Kemble's Kite, is located at
R.A. 03 28.0 Dec +72 00, is about 6th mag and 90'X30', includes red M2 star -
what color do you see. Can you see its 6th mag naked eye? What about using
binoculars to locate then try naked eye. Yes it does look like a kite, don't
you think so?
AJ Crayon
Phoenix, AZ
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