Taking Aim at the Archer
It’s August, and that can
only mean one thing: the Milky Way! This
month, we’re going to focus our attention toward the center of
our galaxy and
survey the area just to the north of the Sagittarius
“Teapot” asterism. There, we
find some wonderful celestial
trophies to add to our collection.
Above: Summer star map adapted from Star
by Phil Harrington.
Finder chart for this month's Binocular Universe. Chart
adapted from Touring
Binoculars Atlas (TUBA)
start at the star Kaus Borealis [Lambda (?)
Sagittarii], marking the top of the Teapot's lid. The name translates from the
Arabic for "northern bow," an apt title since it often represents the
top of the Archer's drawn bow in formal portrayals. Through binoculars, it shows
a warm, orangish tint, an indication of its type K spectral designation.
1 degree to the northwest of Kaus Borealis, we find the small, densely packed
globular cluster M28. Although not as eye-catching as some other nearby
globulars, M28 is still worth a glimpse. Through my 10x50s, M28 reveals itself
as a fuzzy "star." Even through my 25x100 big binoculars, it still
looks like a nebulous puff of unresolved stardust. That's also the impression it
left with Charles Messier when he discovered it on July 27, 1764. He recorded a
"nebula containing no star... round, seen with difficulty in 3˝-foot
[focal length] telescope." The true nature of M28 went unrecognized until
William Herschel saw it as a "star cloud" through his much larger
The orangish star Kaus Borealis is joined by M22 (left) and M28 (right) in
this portrayal based on the view through the author's 10x50 binoculars.
brighter and larger globular lurks 2.5 degrees northeast of Kaus Borealis, just
beyond a triangle of three stars. M22 is one of summer’s true showpiece objects, outclassing – in
my humble opinion, anyway – the Hercules Globular, M13.
Part of the appeal must be credited to its starry surroundings.
But even beyond that, M22 is a real showpiece.
Viewing through 10x50 binoculars, I record a round, fuzzy globe of light
that is punctuated by a brighter central core, but with nary a hint of
resolution. Some comment that the
core appears somewhat triangular, though to my eye it's almost perfectly round.
Through my 25x100s, M22's outer halo shows a grainy texture, as if on the
verge of resolution. A few faint
pinpoints of light poke out from around the edges, but I am not sure if those
are true cluster stars or simply foreground intruders.
cluster NGC 6716 is centered on the Touring
the Universe through Binoculars Atlas (TUBA) finder chart above.
One of the cast from the Astronomical League's Deep-Sky Binocular List,
NGC 6716 is made up of about three dozen stars.
Only four break the binocular barrier, however.
The rest blend into a subtle mist spanning 7'.
Several brighter suns surround NGC 6716 and tend to muddy the issue of
exactly where the cluster begins and ends. One, 7th-magnitude SAO 161947,
especially stands out for its orangish color.
It lies just 12' to the west-northwest of the cluster's center.
also see open cluster Collinder 394
(Cr 394) centrally plotted on the chart. Although
some sources credit as many as 50 stars belonging to Cr 394, binoculars resolve
only a small, ill-defined quintet of 9th-magnitude suns that is easily lost
against the starry environs. As a
hint, the center of Cr 394 is just southeast of the halfway point between NGC
6716 and the 5th-magnitude field star 29 Sagittarii to the west-southwest.
you identify 29 Sgr, can you also see a second, slightly fainter point just to
its west? That's BB Sagittarii,
a Cepheid variable star. Looking
like a golden ember, BB varies only slightly between magnitudes 6.7 and 7.3 with
a period of just over 6.6 days. Some
studies suggest that BB is also an outlying member of Cr 394.
let's shift to the upper left-hand (northeast) corner of the finder chart for NGC
It lies 1.5 degrees west of 5th-magnitude Nu (?)
Sagittarii. While many observing
handbooks pass right by in favor of other Sagittarius objects, I thought it
might be appropriate to stop here for a moment. The cluster's weak concentration
and relatively large apparent size, roughly half a degree in diameter, can make
it difficult to identify through telescopes.
But binoculars readily display about 20 scattered stars.
Look for a triangular asterism of 7th-magnitude stars with many fainter
suns set within.
you can see from the list below, we have only scratched the surface of all this
region of Sagittarius has to offer. Give
each a try and send me your observations. I'd
love to include them in a future column when we next return to the Archer.
month: we will search out some late summer deep-sky delights.
Until then, remember that two eyes are better than one!
About the Author:
Harrington's latest book is called Cosmic Challenge. Visit
his web site www.philharrington.net
for more information.
copyright 2013 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