Sky & Telescope - March 2019 - 34

Herschel Catalog

to plan my program for the last 100+ Herschel objects. My
conversations with Wolfgang and the recoating of my 16-inch
and the 21-inch Manka scope encouraged me to go for it.

pu FOUR PARTS TO A WHOLE The Trifid
Nebula (M20, NGC 6514), a star-forming region
in Sagittarius, was initially assigned three
entries by Herschel. He added a fourth designation - in a different class - later (entries
highlighted at right).

However, some years ago I read that
several amateur astronomers had actually accomplished the feat of tallying
all 2,500+ Herschel objects, including
Sky & Telescope Contributing Editor Rod
Mollise (see S&T: Aug. 2012, p. 60). Sue
French also let me know by email that
Larry Mitchell logged 2,508 Herschel
objects. While I was corresponding
with Jim Mullaney about these achievements, he suggested that I contact deepsky expert Wolfgang Steinicke about
tackling the remaining objects in the
Herschel catalogs.
Wolfgang shared details with me on
his observations of the so-called nonexistent objects (largely open clusters)
conﬁrming to me that most of them
did, in fact, exist. This left only a handful of objects that have not been found,
some of which may or may not have
been comets. Once I knew how many
galaxies, clusters, and nebulae deﬁnitely remained in my quest, I was able
34

M A RCH 2 019 * SK Y & TELESCOPE

Confusion in transcribing across various catalogs has led
to some objects being listed with wrong NGC numbers.
Depending on the source, there are 36 to 50 duplicate
observations by Herschel himself of objects that are listed
under two or more Herschel numbers. The Triﬁd Nebula and
NGC 2264 together account for six Herschel numbers: Four
numbers are assigned to sections of the Triﬁd Nebula and two
to NGC 2264, which consists of the Cone Nebula and the
Christmas Tree Cluster.
One example of an object listed
under the wrong designation is
NGC 5570. I tried to observe it
one night in the spring of 2016 but
couldn't see anything at the location
marked in Uranometria 2000.0. I did
see other galaxies near that spot, but
nothing where NGC 5570 was supposed to be as shown on the chart.
As it turns out, NGC 5519, and not
NGC 5570, is the true Herschel
Class III object 12.
One of the nonexistent objects
that I was able to eliminate on my
own is NGC 6847 in Vulpecula. I
used the STScI page to scan the area
near it and found that the planetary
nebula NGC 6842 ﬁts the description of Herschel Class II 202. The
only objects that I consider truly nonexistent are either NGC 420 or NGC
421 (depending on which of these
two objects is taken to be the false
detection), NGC 3401, and possibly
NGC 5621 (but it may have been
observed by John Herschel). Some
might consider NGC 1908 to be nonexistent, but I believe that the ﬁeld
of NGC 1908 does show a pattern
of stars that could be mistaken for a
cluster - and I was able to ﬁnd it.
I wanted to make sure that I
had covered all possibilities and so
I decided to observe other deep-sky
objects in the ﬁeld of view of Herschel objects, in case one of them
might be the object that Herschel
actually observed. Another questionable object is NGC 4317, which is
listed as a faint star. On the STScI
image of the ﬁeld of NGC 4317, I

TRIFID NEBUL A: TODD BOROSON / NOAO / AUR A / NSF; CATA LOGS: PHILOSOPHICA L TR A NSACTIONS OF THE ROYA L SOCIE T Y OF LONDON (2)

True Source or Not?

Sky & Telescope - March 2019

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