Wednesday, June 29, 2016 The Nugget Newspaper, Sisters, Oregon
Stars over Sisters
By ron thorkildson
Correspondent
The realization that vari-
ous types of celestial objects
are not distributed uniformly
throughout the night sky
usually comes to nascent
observers sooner rather than
later. The constellations of
winter contain many of the
finest open star clusters that
are comprised of relatively
young, nearby stars.
Two well-known exam-
ples are the Pleiades in
Taurus and the Bee Hive in
Cancer.
Conversely, there is
another category of stel-
lar groupings that populate
summer skies in greater
numbers than at other times
of the year. Called globular
clusters, they are densely
packed collections of much
older stars that exist, in most
cases, on the outer edge of
our Milky Way galaxy.
Two of the biggest and
brightest are found in the
constellation of Hercules.
Approximately one-
third the distance from Eta
Herculis southward to Zeta
Herculis in the Hercules
“Keystone” lies M13, the
biggest and brightest globu-
lar cluster north of the celes-
tial equator. Sometimes
referred to as the Great
Hercules Cluster, this object
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was discovered by Edmond
Halley in 1714, and cata-
logued by French astrono-
mer Charles Messier on June
1, 1764. Later Sir William
Herschel turned his superior
telescopes on this body and
in 1787 he wrote, “…M13
is a most beautiful cluster of
stars. It is exceedingly com-
pressed in the middle and
very rich.”
This magnificent clus-
ter contains about 300,000
stars packed into a vol-
ume of space equal to 145
light-years in diameter.
Astronomers estimate its
age to be about 11.6 billion
years (more than twice as
old as the sun), while its dis-
tance from the earth is some
25,000 light-years.
Hercules’ second impres-
sive globular cluster, M92,
is situated some 12 degrees
to the northeast of M13. It
was discovered by German
astronomer Johann Bode
in 1777; Messier found the
cluster in 1781 and made it
the 92nd entry in his cata-
logue of non-stellar objects.
As ancient as M13 is,
M92 is even older. Based
on the cluster’s extremely
low metal content, astrono-
mers believe that it probably
formed just after the Big
Bang as primordial mate-
rial yielded the first galax-
ies. The distance to M92 is
measured at about 26,700
light-years.
Due to the precession of
the earth’s axis of rotation,
M92 occasionally passes
to within one degree of the
North Celestial Pole (NCP).
The last time this occurred
was about 12,000 years ago
and the next time will be
around the year 16,000 AD.
So instead of a star marking
the location of the NCP, as
Polaris does today, M92 will
become the “North Cluster”
object.
Both M13 and M92 are a
favorite targets for summer-
time star gazers. Venus was
squarely behind the sun on
June 6; Mercury will do the
same on July 6. As a result, it
won’t be until the end of the
month before the two infe-
rior planets make an appear-
ance very low on the western
horizon.
Still in Leo, Jupiter’s bril-
liance dominates all other
luminaries in the western
sky. But it continues to sink
lower in the west, and by
the end of July the interval
between sunset and Jupiter-
set shrinks to less than two
hours.
After spending the entire
month of June in retrograde
motion through Libra, Mars
will reverse its path and
begin moving eastward
again. It will be near the head
photo by adam bloCk/mount lemmon sky Center/university of arizona
Located in the constellation of Hercules, globular star cluster M92 is one
of the oldest objects visible in our part of the universe.
of the scorpion by month’s
end. The Red Planet sets at
12:41 a.m. on July 31.
Saturn is in southern
Ophiuchus this month, still
well-placed for observation.
Although it dims slightly as
the month progresses, almost
any backyard telescope will
reveal the planet’s glorious
ring. The best time to view
Saturn is when it’s near the
meridian, about 9 p.m. local
time as the month expires.
As the month begins,
a fading moon goes
dark on July 4. Between
Independence Day and July
19 (the Full Buck Moon),
the night sky gradually
brightens. The waxing first
quarter moon occurs on July
11; the waning last quarter
on July 26.
If you would like to learn
more about the night sky, or
share what you already know
with like-minded folks, con-
sider coming out for the next
Stars Over Sisters starwatch
to be held on Saturday, July
30. Proceedings begin at 9
p.m. with a presentation in
the SPRD building. After
the talk, all are invited out-
side to observe the night sky
through telescopes provided
by local amateur astrono-
mers, weather permitting.
The event is free.
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