[sac-forum] Call for Observations
- From: "AJ Crayon" <acrayon@xxxxxxx>
- To: "SAC Forum" <sac-forum@xxxxxxxxxxxxx>
- Date: Thu, 23 Oct 2008 10:31:48 -0700
Here are 3 months worth of the observations lists. There is still time for
Lacerta so if you have some spare observing time why not give this a try. The
December list has already appeared in the newsletter but the new one is for
January 2009 and covers the Trumpler Class of classifying open clusters.
I'll not be observing this weekend but don't let that stop you. Get out and
give these objects a try regardless of your telescope size and then, of course,
send me the observations for inclusion into the newsletter.
So far we haven't done anything in the constellation of Lacerta. Surprisingly
it contains open clusters and galaxies, which is what waits us for this
session. Starting from the western part, near Cygnus, is NGC7209, a bright
open cluster that is in both the 110 Best NGC and Herschel 400 lists. It has
about 25 stars from 9th mag. Do you see it as scattered or compressed? About
5° south is the barred spiral NGC7223. What about the bar and spiral arms?
Can you see them? Moving towards the northern part of the constellation is the
open cluster IC1422 and its 25 or so stars. The second galaxy, NGC7265, is
same magnitude as NGC7223 but is larger and has a lower surface brightness.
NGC7296 is on the Herschel 400 list is small and has 20 stars, so it may not be
that easy to find. The last selection is the elliptical galaxy NGC7426.
Beware it is just to the east of SAO72851, a double star, whose primary is mag
5.7.
Our constellation, for December, is Piscis Austrinus meaning Southern Fish.
There are numerous galaxies in this constellation that should be within reach
of 8" telescopes. So, let us hope the weather favors us for this unexpected
trip below the celestial equator. Starting from the western end is the
asterism titled Air Balloon and found at R.A. 21h 30.0m Dec -25° 30'. It is
about 45' in diameter, contains a nice collection of 7th and 8th mag stars and
is described as a closed loop of stars. What does it look like to you? Now on
to the galaxies and we start with NGC7135 that is mag 11.7, less than 3' and
just southeast of 3 stars with mag 9.5, 10.3 and 11 that form a nice right
triangle. Now we move on to a galaxy group containing 4 or 5 galaxies. The
first is the spiral NGC7172, almost 12th mag, elongated and sporting an
equatorial dust band. Can you spot it? The other galaxies are located just 7'
due south and consist of NGC7173/74/76. They are located between 2 stars of
9th and 10th mag in a north of northeast position. NGC7173 is the northern
most, is 12th mag and somewhat elongated in a southeast position. NGC7174 is a
little larger, somewhat elongated in an easterly position and at mag 13.3 is
the faintest of the group. The last is NGC7176 only very slightly elongated
with an uncertain position angle. Also involved in this triple grouping is the
mag 11.9 galaxy LEDA198475 located between NGC7173 and NGC7174. This grouping
of galaxies is also known as Hickson 90. Moving on to the others, we continue
with 11th mag NGC7314. This galaxy is quite elongated, not doubt because we
are seeing the bar of this barred galaxy. Now mosey on to the spindle shaped
IC5269, a rather small, elongated galaxy of mag 12.2. Next is the nearly
edge-on NGC7361 at mag 12.3. Can you detect a little brighter middle? Last we
have the very elongated IC5271 at mag 11.6. What do you see in the middle?
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 having 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 better understand 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. NGC1512
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.
worth
AJ Crayon
Phoenix, AZ
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