Sky & Telescope - December 2022 - 22

JERRY MACON (2)
Royal Rewards
Observatory Sky Survey (POSS) photographic plates. (For
a nice roundup of several of Abell's planetary nebulae, see
S&T: Jul. 2017, p. 34.) Using 94× and an O III filter, I spied
it 25′ south-southwest of the gold-hued, 6th-magnitude star
HD 223173, and I even suspected it when I removed the
filter. At 117× I could see it unfiltered with averted vision as a
soft glow a full 1′ wide, only 1.5′ southeast of an 11.3-magnitude
star. Several fainter stars are scattered across the immediate
area, including a distracting one of magnitude 13.2 on
the southeastern edge of the planetary. Increasing to 260×,
the 14.9-magnitude central star emerges with direct vision,
while the disk is a soft, ill-defined glow.
Abell 84 is challenging to find as it lies far from any
LONELY OUTPOST Abell 84 is possibly the hardest planetary
nebula to star-hop to on our celestial tour. Lying around 6,400
light-years distant, its apparent size of about 2.5′ translates to a true
dimension just shy of 5 light-years.
bright naked-eye stars. It's situated more than 9° southwest
of 2.2-magnitude Alpha (α) Cassiopeiae (also known
as Schedar) near the border with Andromeda. For more
than 50 years after its discovery it held the distinction of
being the planetary nebula with the largest right ascension,
appearing last in many lists (until amateur astronomer
Matthias Kronberger discovered Kronberger 50 in 2007).
It sits 12′ northeast of 7.5-magnitude HD 223152 and is
7′ west of a 4′-wide pair of 10th-magnitude stars. In my
10-inch at 94×, it's invisible until I add an O III filter, which
then reveals a faint, 1.5′-wide disk with an 11.3-magnitude
star on its eastern side. Keeping the filter, at 117× the
nebula's edges are very ill-defined, and I can detect a slightly
brighter central area running east to west. Removing the
filter and bumping up to 200× and 260×, I was surprised to
still glimpse the planetary as an amorphous disk.
Lost Brothers
A careful star-hop 1.8° west-southwest of Alpha Cassiopeiae
will bring you to our next target, the nearly stellar, 12thmagnitude
Humason 1-1. It's the faintest of three planetaries
that Milton Humason, Hubble's long-time assistant
at Mount Wilson Observatory, discovered. He found them
in the early 1920s on objective-prism plates taken with a
10-inch f/4.5 Cooke refractor.
Hu 1-1 lies 2′ southeast of a close pair formed by 11.7- and
12.6-magnitude stars. At 150× in my 10-inch, it begins to
look like a bloated star with a dull gray-blue hue, while at
200× it's noticeably nonstellar. Under good seeing conditions,
bumping the magnification all the way up to 520×
allows me to detect the nebula's small, dark center. This
planetary takes magnification splendidly because it has a
high-surface-brightness annulus, hosts a central star too
faint to be visible, and achieves a high altitude in the sky for
viewers at mid-northern latitudes.
Our next target is as small as the previous one and lies just
BRIGHT SURPRISE Despite it being one of the brighter and
easier planteray nebulae to find among our targets, Abell 2 is actually
one of the least interesting visually.
2.5° farther southwest. Russian-born astronomer Alexander
Vyssotsky accidentally discovered Vyssotsky 1-1, as it came
CASSIOPEIA'S TREASURES One of the most recognizable constellations
harbors a pleasing wealth of planetary nebulae. Spend your winter
nights enjoying this curated selection.
22 DECEMBER 2022 * SKY & TELESCOPE
Sky & Telescope - December 2022

Table of Contents for the Digital Edition of Sky & Telescope - December 2022
