Table of Scorpius
July, this column visited M6 and M7, two of the finest open star clusters
visible through binoculars in the summer – or for that matter, any – sky.
Both lie near the tail of Scorpius, the Scorpion. This
year, we return to this celestial arthropod to discover more tantalizing
Above: Spring star map adapted from the book Star
Watch by Phil Harrington
Above: Finder chart for this month's Binocular Universe.
Chart adapted from Touring the
Universe through Binoculars Atlas (TUBA), www.philharrington.net/tuba.htm
may have heard the phrase the "Table
of Scorpius." The "Table"
covers the area circled on the all-sky map above, although you shouldn't expect to see a
piece of furniture among the stars. This
“Table” most likely refers to a place. The
term was coined by John Herschel during his trip to
in the 1830s.
In his book 1001 Celestial Wonders to See Before You Die, author
Michael Bakich suggests that this is “a reference to Table
Mountain, which he could see every night as he gazed at the stars from his
this same time, Herschel also christened a naked-eye asterism within the Table as the "False Comet." (Note that there is some disagreement in
the literature as to the origin of the “False Comet” asterism. Some
sources cite a much more recent origin, in the 1980s.)
While the area may give the impression of a comet, the term may again
to a geographical location. Turning
again to Bakich’s book, he suggests “Although I haven’t confirmed it
by reading Herschel’s words yet, I’m certain he named his ‘comet’ after False
Bay, the place where his ship first touched land in
binocular targets combine to create Herschel’s False Comet.
Zeta Scorpii, where the
Scorpion’s body hooks eastward, marks the comet’s “coma.”
Zeta is a striking double star through binoculars.
The brightest of the pair, often abbreviated Zeta-2, displays an obvious orange
tint, while fainter Zeta-1 is blue-white. In
reality, however, they are not related to each other.
Zeta-2 lies 200 light years away, while Zeta-1 is an impressive 6,000
light years from us. A third,
unrelated star (6th-magnitude SAO 227392) just to the south creates a nice
equilateral triangle with the Zetas.
is the brightest member of a collection of young, hot suns called the Scorpius OB1 Association, or in shorthand, Sco OB1.
When we gaze their way, we are looking toward the Milky Way’s next
inward spiral arm, called the Sagittarius Arm.
tail of Herschel’s False Comet is made up of several close-set open clusters.
Look half a degree north of Zeta and you’ll spot NGC
6231 at the core of Sco OB1. This
small, but bright target was discovered by the Italian astronomer Giovanni Batista
Hodierna (1597–1660), who included it on his list of 40 nebulous objects
published in 1654. Some 120
searingly hot blue-white stars are crammed inside this tight cluster.
They look relatively faint through binoculars because we are seeing them
from across such a vast gulf. But if we could somehow magically reduce that
distance to the same distance as the Pleiades cluster (380 light years), the
brightest stars in NGC 6231 would outshine Sirius in our sky.
another degree to the north, we come to the little-known cluster Collinder 316. Its stars
are loosely gathered across 2 degrees – that’s four Full Moons stacked end to end.
No wonder so few telescopic observing guides mention it.
We binocularists, on the other hand, can enjoy some three dozen of its stars
ranging in brightness from 6th to 9th magnitudes.
may notice that the eastern edge of Cr 316 contains a few more stars than the
western. Those form a more
concentrated sub-cluster of stars cataloged separately as
identified as Harvard 12 in some references).
Trumpler 24 is characterized by an arc of three 6th-magnitude stars
Left: A sketch the "False Comet" by the author through his
North is up.
tail end of the tail is marked by the compact open cluster NGC 6242. NGC 6242 lies
between Collinder 316 and Mu Scorpii. Binoculars
resolve a lone 6th-magnitude sun attended by four or five 9th-magnitude points
of light and the subtle glow of fainter, invisible cluster members.
In all, approximately 45 stars down to 11th magnitude belong to NGC 6242.
could go on, but space is running short. Before
closing for the month, however, here
are some additional suggestions for readers who want to continue exploring this
rich region of the summer sky.
Be sure to print the PDF
version of this column to bring
outside with you. Click on the 'Download
this Document' link at the top of this page to download the PDF
you may print or save for future use.
Have a question, a comment, or a suggestion for future columns? I'd love to hear it. Drop me a line at email@example.com.
We'll continue exploring
the Milky Way next month, so if you have some favorite objects in and around
Sagittarius, drop me a line and tell me about them.
Meanwhile, until then, remember that, for summer stargazing, two eyes are
better than one!
Phil Harrington is a contributing
editor to Astronomy magazine and author of 9 books on astronomy. Visit his web site at www.philharrington.net
Phil Harrington's Binocular Universe
is copyright 2011 by Philip S. Harrington. All rights reserved. No
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