From: LABBEY@GITVM1.GATECH.EDU
Subject: The Focal Point for April 1995
THE ASTERISM GAME
by Jack Kramer, Libertyville, Illinois
is, it's a grouping of stars that appear sufficiently near each other
in the sky so that we tend to associate them with one another. They may
or may not be related in terms of their position in space, age, or
gravitational interaction. For example, the "Coat hanger Asterism",
also known as "Brocchi's Cluster", in Vulpecula is a true open cluster,
designated as Collinder 399 (Cr 399). In the sky it appears with an
upside-down coat hanger shape just to the northwest of the familiar
arrow-shaped constellation, Sagitta. It's small and not easily seen
unless the sky is sufficiently dark, but it's an excellent object for
binoculars. The first time I noticed it was not in the sky, but rather
on a photograph I had taken of the area about eight years ago.
At the eastern edge of Cr 399 is the 8.8 magnitude open cluster NGC
6802. The brightest members of this cluster are 14th magnitude, which
explains why it appeared simply as an irregularly-shaped hazy spot in
the 10" scope from my backyard.
On the other hand, there's the "Leaping Minnow" asterism in Auriga,
located about 4o east of the star 3 Auriga; it's a prominent little
grouping composed of the stars 14, 16, 17, 18 and 19 Auriga. Although
it's located in an area full of open clusters and diffuse nebulae, the
Minnow is not itself a true cluster - just a chance juxtaposition of
stars seen as a slightly arched line that could remind one of a fish
jumping out of water. I first noticed this asterism while aimlessly
wandering the sky with a copyscope.
The two objects cited above are perfect examples of star patterns
known as asterisms. In some cases where they've been designated as
clusters, there is disagreement as to whether they are, in fact, true
clusters. The Saguaro database, for example, shows some objects
cataloged as clusters, yet the comments field indicates that this is
questionable with the notation "asterism?" But asterisms in general
are small, tight groupings that prompt us to feel that from our
perspective, the stars ought to be related.
Some have been given fanciful names that reflect how they appeared to
certain observers. One called "Kemble's Cascade" was named after the
observer, Lucien Kemble, who called attention to it. This asterism is
located in the constellation Camelopardis, and it appears as a long
string of stars beginning near the 8th magnitude cluster NGC 1502. The
coordinates of the cluster are 4h 07.7m, +62.2'.
Checking my records, I've observed NGC 1502, but there's no mention of
having seen the Cascade. However, I observed the cluster from my
backyard with the 10" scope and an eyepiece that gave a field of about
.8', while this asterism spans a distance of about 3'. So you'd need a
wider field to notice it readily. This is an ideal object for binoculars
or a wide field telescope. Once this area of the sky is better
positioned, I intend to check out Kemble's Cascade with the copyscope.
Of course, an asterism need not have an unusual shape; it could be just
a formless group of stars. (Some undiscovered possibilities: Garza's
Glob? Barlow's Blob? Andree's Agglomeration?) In all cases, they're
great objects for binocular users or those who have a small, wide field
telescope. Sometimes when we run across one unexpectedly, there's a
thought that maybe we've discovered another cluster. This sends us to a
star chart to check it out. The chart may not even show the stars, and
if shown, they may not be identified in any particular way. For example,
the Tirion Sky Atlas 2000 shows the Coat hanger stars with no
designation. The more detailed Uranometria identifies the group as a
cluster, with both common names.
Here's an example of a personal "discovery". While wandering with the
copyscope in Coma Berenices, I came across a group of eight stars
arrayed in the shape of two diamonds that suggested a greyhound dog
running at full stride - the star at lower left being the front paw,
the star farthest to the right the rear paw, and the brightest star
being the head. The group spans just over 1o and is about 15o east of
the star b Leonis. When I first spotted the asterism, I was unable to
locate it on any chart. On the next night, I finally broke down and
used the setting circles; this got me into the general area in the
Uranometria, where I found the asterism pictured at 12h 46m, +13.5'.
The stars range between 7th and 9th magnitude. One problem is that the
increments used in sizing the star images on charts often don't
represent how they actually appear in the sky, and you also have to
bear in mind how the image in your scope is turned upside-down or
right-to-left. The galaxies in the field, NGC 4659 and 4689, are 13.3
and 12.8 magnitude, respectively, so they weren't visible in the
copyscope from my backyard.
The finding of asterisms is not something you accomplish by poring
over star charts. It's a real observer's undertaking where you have to
get out under the night sky with some wide field optical aid and just
start sweeping. For those who presently use only binoculars, it helps
you to learn your way around the sky and you could become real asterism
experts. If you find a grouping for which there doesn't seem to be any
official designation, well then name it after yourself! Often the
astronomy press will mention a particular asterism with an obscure
name, so another observer has already beaten you to that group. But
with all those stars up there, think of the potential asterisms you
could claim as your very own!
REPRINTED FROM ASTRONET, ISSUE 12.
FOR MORE INFORMATION, PLEASE CONTACT resource@rahul.net.
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- T o d d E. V a n H o o s e a r -
``'''vanhoose@lalaland.cl.msu.edu - vanhoose@msu.edu - vanhoose@lalaland.cl.msu.edu
(._.) Michigan State University - East Lansing, MI USA
(_) Computer Laboratory - Department of Communication
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