Sky & Telescope - January 2024 - 57

ADAM BLOCK
yard scopes), while the feeble red dwarf
is dim but definite.
Fuzzy Fishing
My next fish, 5.0-magnitude 39 Eridani,
shows plainly in finderscopes a tad more
than 2½° south and slightly west of the
tandem dwarfs. Orangey 39 Eri harbors
an 8.5-magnitude pure-white star 6.4″
to the southeast. The tightly spaced pair
is a snap in both scopes, again using my
preferred 9-mm ocular. By the way, 7thmagnitude
BM Eridani, a deeply orange,
long-period variable star, sits ¼° southwest
of 39 Eri. The warm-hued suns are
unrelated: 39 Eri resides 230 light-years
from Earth, whereas BM Eri is nearly six
times farther away.
A 2½° drop south from 39 Eri
rewards us with the planetary nebula
NGC 1535 - maybe! Essentially a
teeny, fuzzy disk, NGC 1535 is easy to
miss if you're a star-hopper. My advice
for hooking this cosmic small fry is to
center 39 Eridani in your scope at low
magnification, then descend slowly
and look for two starry landmarks.
The first is a solitary 8th-magnitude
star. The second, ½° farther along and
a bit westward, is a 10′-wide triangle
formed by three 9th-magnitude stars.
NGC 1535 lies south-southeast of the
solitary star and east of the triangle.
Those helpers, plus the planetary, share
a low-power field.
Boasting a magnitude of 9.6 and a
diameter of 20″, NGC 1535 is actually
a moderately prominent planetary
Eridanus Catches
Object
Type
Rigel
Σ649
Σ636
40 Eri AB
40 Eri BC
39 Eri
NGC 1535
Double star
Double star
Double star
Double star
Double star
Double star
Planetary nebula
provided my south sky isn't too hazy
or turbulent. The 8th-magnitude
landmark star noted above helps me
achieve sharp focus when I play around
with different eyepieces. At 100×, the
planetary is larger and much more distinct
than in the 50× view, though any
additional magnification beyond 100×
doesn't really help.
What does help is threading an
pNOT A REAL PLANET This relatively bright
planetary nebula, NGC 1535, has nothing to do
with planets. The name " planetary " was coined
by 18th-century astronomer William Herschel,
who commented that the tiny, round nebulae
he viewed in his telescope resembled distant
planets. The Neptune-like aqua hue of NGC
1535, evident in this image, is apparent in midsize
amateur scopes. However, the nebula's
central star is difficult to detect in small, citybased
instruments.
nebula. But because this healthy specimen
lies nearly 13° below the celestial
equator, it climbs less than 29° above
my south horizon. The lower portion of
anyone's night sky frequently exhibits
turbulent seeing. In my case, the low
south is also horribly light-polluted.
Fishing for fuzzies in a murky gray
sky is, to put it politely, a challenge.
Thankfully, NGC 1535 isn't terribly
diffuse, and its luminous, bluish disk
can pierce the pollution.
Admittedly, NGC 1535 can be hard
to detect in my refractor. At around
50×, it materializes as a teeny disk,
Ultra-High Contrast (UHC) filter into
the eyepiece barrel. By blocking certain
unwanted wavelengths of light, a UHC
increases contrast between nebula and
sky. Our tiny spherical planetary, NGC
1535, really pops with the aid of the
filter. And if you have a doubly ionized
oxygen (O III) filter, try it. An O
III delivers even stronger contrast. It's
important to remember, though, that
while greatly darkening the sky, these
narrowband filters also slightly attenuate
the nebula. I find the O III view a bit
too dim in my 120-mm refractor.
Seeing Is Believing
NGC 1535 is substantially more
impressive in my 8-inch reflector than
in the smaller refractor. My trusty
9-mm eyepiece yields a well-defined
disk that seems (perhaps in my imagination!)
subtly greenish-blue. Intriguingly,
the almost azure disk is somewhat
brighter at its center - possibly a
blurry hint of the nebula's 12.2-magnitude
central star. And I don't need to
apply either a UHC or O III filter for a
satisfying view - NGC 1535 is bright
enough in the 8-inch to be appreciated
in its purest light.
The bottom line for the top of
Mag(v)
+0.3, 6.8
5.8, 9.0
7.1, 8.5
4.4, 9.3
9.5, 11.2
5.0, 8.5
9.6
Size/Sep
9.4″
21.3″
3.7″
82.7″
7.9″
6.4″
20″
RA
5h 14.5m
5h 08.3m
5h 03.0m
4h 15.3m
4h 15.3m
4h 14.4m
4h 14.3m
Dec.
-08° 12′
-08° 40′
-08° 40′
-07° 39′
-07° 39′
-10° 15′
-12° 44′
Angular sizes and separations are from recent catalogs. Visually, an object's size is often smaller than
the cataloged value and varies according to the aperture and magnification of the viewing instrument.
Right ascension and declination are for equinox 2000.0.
Eridanus is that this selection of little
fish deserves a place on your January
hit list. Special mention goes to the
pint-sized planetary NGC 1535, which I
consider to be a prize catch considering
the blanched and turbulent state of my
sorry southern sky.
¢Contributing Editor KEN HEWITTWHITE
first reeled in NGC 1535 40 years
ago while scanning the low south with
an 8-inch Schmidt-Cassegrain telescope
from a motel balcony. Fortunately, nobody
called the police.
sk yand tele scope .o r g * JANUARY 2024 57

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Sky & Telescope - January 2024

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