Sky & Telescope - December 2020 - 22

Catalog Celebration

GLOBULAR CLUSTERS Start
high in the west-southwestern
sky with the tiny constellation
Delphinus, the Dolphin, off the
"nose" of Pegasus. Here you'll
find two of the most northerly
globular clusters in the Caldwell
Catalog, C42 (NGC 7006) and
C47 (NGC 6934). C42 is the
dimmer of the two globulars, at
least as seen from Earth, and
with good reason: At 135,000
light-years, it lies more than
two-and-a-half times as far
away as C47, well beyond the
disk of the Milky Way.
C47

observer. One evening in 1995 he was struck by the fact that
many worthy deep-sky objects were either never observed by
Messier, or at least not included in his catalogs. As Moore
wrote in the foreword to Stephen James O'Meara's Deep-Sky
Companions: The Caldwell Objects, ". . . there are many other
objects of equal or greater interest than those with 'M' designations. Many of these non-Messier sights are shamefully
neglected . . . . Why not draw up a catalog to list objects not
identiﬁed by Messier?"
The next morning Moore wrote up a list of 109 deep-sky
objects spread across the entire sky, including challenges for
those with large telescopes. He decided to arrange his list by
declination, so that observers could quickly zero in on the
most southerly (or northerly) objects available to them, and
get an accurate tally of how many were within their reach.
Since the 'M' designation was already taken by the Messier
catalog, Moore invoked his full last name, Caldwell-Moore,
called his list the Caldwell Catalog, and assigned 'C' numbers
to the objects. Then, as he wrote, "Having completed my list,
I put it in an envelope and sent it off to Sky & Telescope. To be
candid, I thought very little more about it. Creating the list

PLANETARY NEBULAE A large swath of
the western sky offers no fewer than five
Caldwell planetary nebulae. Start in the
northwest with C6, the Cat's Eye Nebula
(NGC 6543), in Draco, just about halfway
between Delta and Zeta Draconis. A little
more than 20° to the southeast, in the western wing of Cygnus, the Swan, you'll find
C15, the Blinking Planetary (NGC 6826).
Another sweep almost twice as
much farther east takes you to
Andromeda and C22, the Blue
Snowball (NGC 7662), flying
near the zenith on late-autumn
evenings. Now pivot south and
C22
swoop down low to Aquarius to

had been an interesting exercise, but would anyone else be
interested in it?"
The editors at Sky & Telescope were indeed interested.
Thanks to the widespread availability of Dobsonian reﬂectors and affordable Schmidt-Cassegrains, interest in deepsky observing had been increasing since the 1970s. Moore's
new list of deep-sky objects, chosen for their visual splendor
and astrophysical signiﬁcance, and composed for a global
audience, seemed certain to capture readers' attention. As
former editor in chief Rick Fienberg explains, "He [Moore]
sent us his letter and list of objects and said we could do
with it as we please. We responded by asking him to write
an article explaining his rationale for compiling the list
and for ordering it by declination from north to south.
He responded by saying he was too busy to write such an
article, but that we were welcome to adapt his letter for
an article ourselves. That's why Barlow Pepin is the coauthor [in the December 1995 issue] - he was the editor
assigned to turn what Patrick sent us into an article. Patrick
approved the article before we published it and was thrilled
at how it came out."

find C55, the Saturn Nebula (NGC 7009).
The planetaries listed so far are small, but
with high surface brightness, so they hold
up surprisingly well under moderate light
pollution if you use high magnification. But
you'll want the opposite - dark skies and
low magnification - to pick up the fifth and
final Caldwell planetary on this tour: C63,
the Helix Nebula (NGC 7293). The large
apparent size and low surface
brightness of the Helix are due to
its proximity: At a little more than
500 light-years away, it's much
closer than the other planetaries listed here, which range from
1,400 to 3,200 light-years away.
C6

DECEMBER 2 02 0 * SK Y & TELESCOPE

C 42 & 47: ESA / HUBBLE / N ASA; C22: M ASIL IM AGING TE A M; C6: NORDIC
OPTICA L TELESCOPE / RO M A NO CORR A DI / ISA AC NE W TON G ROUP OF
TELESCOPES, SPAIN

C42

Sky & Telescope - December 2020

Table of Contents for the Digital Edition of Sky & Telescope - December 2020