Double Cluster and Friends
the dozens of open star clusters that dot the autumn sky, none is more popular
among binocular stargazers than NGC 869 and NGC 884, the famous Double
Cluster in Perseus. Even from
suburban backyards, this striking pair can be seen with the naked eye as a
faint, elongated smudge of light about halfway between the "W" of
Cassiopeia and the northern "tip" of Perseus.
If you have trouble spotting it, scan through your binoculars along a
line extending from Gamma (ã) Cassiopeiae, the center star of the W,
through Ruchbah [Delta (ä) Cassiopeiae] and continuing toward the
southeast. Maintain a straight
course and you will see both clusters as two tiny clumps of stars.
autumn clusters compare to either NGC 869 or NGC 884 singularly, but when you
add both together, the field literally overflows with stars.
Unlike many star clusters, however, which need telescopes to be seen at
their best, NGC 869 and 884 are just as wonderful through binoculars. In fact,
in my opinion, while they are still impressive through telescopes, the narrower
views of most telescopes sacrifice the area's overall beauty.
to 10x binoculars resolve each cluster into a tight knot of white stars against
a star-strewn backdrop. Higher-power
giant binoculars only improve the view by increasing resolution as well as
heightening the radiance of the many colorful red supergiant suns that are
scattered across the region.
I had a chance to watch the clusters through a pair of monstrous 100-mm
binoculars as they just rose above some far off pine trees.
The field teemed with stardust, spilling over and around the distant
pines. The view was magnificent,
creating a magical moment that could never be captured in an image, but whose
image is forever filed away in my mind's astronomical photo album.
discovered the Double Cluster is lost to history, although we do know that their
combined presence attracted the eyes of stargazers as far back as the second
century B.C., when Hipparchus made mention of them in his notes.
Messier apparently knew of the Double Cluster, but never recorded them in
his catalog. Why he ignored them,
but included M40 (a double star in Ursa Major) and M73 (a four-star asterism in
Aquarius), is difficult to understand.
the two clusters actually physically linked to one another?
They almost certainly have some mutual gravitational effect, since NGC
869 (the westernmost cluster) is 7,100 light years away, while NGC 884 is
slightly farther at 7,400 light years. Both
are primarily composed of hot type-A and type-B supergiant, superluminous stars.
Some 200 suns call NGC 869 home, while NGC 884 is made up of about 150
stars. Several red supergiants are
seen in NGC 884, but are conspicuously absent in NGC 869.
Finder chart from TUBA, www.philharrington.net/tuba.htm
you have had a chance to enjoy the Double Cluster, follow an arc of stars to the
north, crossing into Cassiopeia. Look
there, about 2° north of the Double Cluster, for a clumping of faint stars that
form an X-shaped pattern. That's Stock 2, a little-known open star cluster that stands out remarkably
well through binoculars despite its crowded surroundings.
Stock 2's fifty member stars cover a full degree of sky, the same as two
full moons stacked end‑to‑end. About
20 of these stars can be resolved through 7x binoculars, although they only
shine between 7th and 9th magnitude.
Double Cluster (below center) and Stock 2 (circled, above center) are
captured beautifully in this sketch by Rony De Laet (rodelaet in the CN
forums). Notice how the very
faint stars of Stock 2 form a stick figure of a human, in this case
a long, careful look at the stars in Stock 2.
Let your imagination run wild for a moment.
See any pattern among them? Careful
scrutiny will show that the stars seem to fall into four distinctive threads
curving away from the center. My
buddy John Davis from
mentioned to me more than 20 years ago that the brighter stars almost look like
a headless stick figure flexing his muscles, christening it the "Muscleman
Cluster." His legs stretch out
in two straight lines to the east, while his flexing arms curve to the west,
above his long, albeit headless neck. Others
remark that the pattern is more reminiscent of a pirouetting ballerina, again
sans head. Muscleman or ballerina
not withstanding, the next time you are drinking in the beauty of the Double
Cluster, be sure to swing northward and spot Stock 2 in the same field of view.
star chart here shows several other open clusters lying in wait, as you can see
from the list above. All are smaller
and fainter than the spectacular Double Cluster, but are still well worth
hunting down. Take a look at each
and let me know what you find. Post
your observations in this article's discussion thread or drop me a line at firstname.lastname@example.org.
next month, remember that two eyes are better than one.
Harrington is the author of Touring the Universe through Binoculars.
Visit his web site at www.philharrington.net
Phil Harrington's Binocular Universe
is copyright 2009 by
Philip S. Harrington. All rights
reserved. No reproduction, in whole
or in part, beyond single copies for use by an individual, is permitted without
written permission of the copyright holder.