With the bright Moon out
of late evening sky, look high overhead to see the "celestial strongman,"
the constellation of Hercules.
Itís a star pattern in which
the traditional mythological figure is difficult for modern skywatchers to visualize.
Astronomer Robert H. Baker (1880-1962) described its six brightest stars as
a "butterfly with outspread wings." Others sometimes describe those
same stars as outlining the initial "H" for Hercules.
But primitive people seemed
to have no difficulty in picturing these stars as forming the figure of a kneeling
man, and the old Arabic name of its brightest star, Ras Algethi, means "The
Head of the Kneeler."
About 260 B.C., the Greek
poet Aratus noted that "no one knows how to read that sign clearly, nor
on what task he is bent." Yet, it was also the Greeks who apparently declared
that "The Kneeler" was their great hero, Hercules.
Also within Hercules is
quite possibly the most celebrated object in the summertime skies: The Great
Cluster in Hercules, known also as M13. The M, of course, is the initial of
the famed comet observer, Charles Messier (1730-1817).
Messier was deeply interested
in discovering comets but he was plagued by the same trouble that besets all
comet hunters. He kept finding "comets" that were not comets at all
but only star clusters and nebulae. His hopes were dashed so often that for
his own convenience he kept a list of these deceiving objects, which he published
in a catalogue.
To locate Messier 13, look
toward the four stars, known as the "Keystone" that supposedly forms
the body of Hercules.
A keystone is the stone
atop an arch, and has this shape, narrower at one end. Itís between the two
western stars of the keystone that we can find the Great Globular Cluster of
Hercules. Itís about a third of the way along a line drawn from the stars Eta
to Zeta. Actually, it was not Messier, but Sir Edmund Halley (of comet fame),
who first mentioned it in 1715, having discovered it the previous year: "This
is but a little Patch," he wrote, "but it shows itself to the naked
Eye, when the Sky is serene and the Moon absent."
Located at a distance of
about 25,000 light-years, the Hercules Cluster has been estimated to be a ball
of tens of thousands of stars roughly 160 light-years in diameter.
Messier first saw the cluster
in June 1764 and described it as a "round and brilliant nebula with a brighter
center, which I am sure contains no stars."
Today, if you use good binoculars
and look toward that spot in the sky where M13 is you likely will see a similar
view: a roundish glow or patch of light. Moving up to a telescope, the view
dramatically improves. With a 4 to 6-inch telescope, the "patch" starts
to become resolved into hundreds of tiny pinpoints of light. In larger instruments,
Messier 13 is transformed into a spectacular celestial chrysanthemum.