Sky and Telescope - September 2018 - 45

Under the Stars by Fred Schaaf

Harvesting the Autumn Skies
Be prepared to gaze in wonder upon September's diaphanous delights.

N ASA / ESA / HUBBLE HERITAG E TE A M

I

n September you have to observe right
after nightfall to catch the Sagittarius
Milky Way at its highest. But there's
more than just our galaxy's glow to enjoy
on September evenings. Those skies offer
us a generous helping of virtually every
kind of deep-sky object possible.
September's star clouds and diffuse nebulae. Many patches of brighter
naked-eye radiance shine along the socalled summer Milky Way. Six that are
both prominent and well-known are:
the Cygnus Star Cloud, the Scutum Star
Cloud, the Large Sagittarius Star Cloud,
the Small Sagittarius Star Cloud (M24),
the Lagoon Nebula (M8), and the big
open star cluster M7. The next of these
bright naked-eye patches is an impressively intense one that seems to have
escaped naming and therefore fame. A
few years back in this column I dubbed
it both the Gamma Scuti Star Cloud
and also a name befitting its mysteriousness: "the Seventh Glow."
The Seventh Glow forms a compact
equilateral triangle with two famous
Messier nebulae that require optical aid
to see properly. One of these is M16, the
Eagle Nebula or Star Queen Nebula, of
Hubble Space Telescope photographic
fame with its "Pillars of Creation."
The other is M17, most often called
the Omega Nebula, but also variously
known as the Swan Nebula, Horseshoe
Nebula, and Checkmark Nebula (see
Howard Banich's Going Deep column,
S&T: Sept. 2017, p. 57). The triangle of
M16, M17, and the Seventh Glow is only
about 2½° to a side and yet each of the
three is in a different constellation -
Serpens (M16), Sagittarius (M17), and
Scutum (the Seventh Glow star cloud).
September's strip of planetary
nebulae and a poignant supernova
remnant. I always find it remarkable
that the two most famous and prominent planetary nebulae, along with

two other notable planetaries, are all
located within a surprisingly small strip
of the heavens. M57, the Ring Nebula
in Lyra, and M27, the Dumbbell Nebula
in Vulpecula, lie on a line with the
renowned double star Albireo, or Beta
(β) Cygni, which shines about midway
between them. Considerably farther to
the southeast are the other planetaries,
both in Aquarius: the small, intense
Saturn Nebula (NGC 7009) and the
great-in-total-brightness but huge
and thus low surface brightness Helix

evenings every major globular from late
spring's M3 and M5 to autumn's M15
and M2 is reasonably well placed. Fine
open clusters for September evenings
include M11 (midway up the sky); M6,
M7, and M25 (fairly low but quite
visible); M39 (high); and the Double
Cluster in Perseus (still pretty low but
climbing). Summer and winter are poor
seasons for galaxies other than our
Milky Way, but by September the visually greatest external galaxy, M31, is
high enough for good evening views.

NGC 6960, also known
as the Veil Nebula, is
part of the Cygnus Loop
supernova remnant.

Nebula (NGC 7293). Of the sky's finest planetaries, others can be found in
this general region of the heavens - for
instance, NGC 6826, the Blinking Planetary, in Cygnus.
Near the other wing of Cygnus,
the Swan, is a stellar aftermath more
ancient than the planetary nebulae,
one formed from a much mightier stellar demise. It's a supernova remnant,
its arcs and shreds of radiance forming
the roughly 3°-wide Cygnus Loop. The
easiest section of the Loop to find is
NGC 6960, the Veil Nebula.
September's globulars galore
- but also key open clusters and a
galaxy. Summer is the great season of
globular star clusters, but on September

Red, double, variable stars, and
more. September brings us great views
of red Mu (μ) Cephei (Herschel's Garnet Star); Epsilon (ε) Lyrae (the Double
Double) and Albireo; Delta (δ) Cephei
and Rasalgethi (both stars that are
fascinating variable stars and colorful
doubles). There's a dearth of very bright
stars at the time of our all-sky map: The
only ones of 1st-magnitude or brighter
are Arcturus, Vega, Altair, Deneb, and
Antares. But at least this year Venus,
Jupiter, Saturn, and Mars all help
brighten our September evenings.
¢ Contributing Editor FRED SCHAAF
welcomes your letters and comments at
fschaaf@aol.com.
sk yandtelescope.com * S E P TE M B E R 2 018

45


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Table of Contents for the Digital Edition of Sky and Telescope - September 2018

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