Sky & Telescope - January 2021 - 56

JANUARY 2021 OBSERVING
Suburban Stargazer
5h 38m

NGC 1746

Σ 742

Crab Nebula (M1)

+22°

Σ 740
+21°

ζ
TAURUS

AG 313

The Crab glows modestly at magnitude 8.4, but its light is spread over a 6′
× 4′ area. The result is a low-contrast
cloud that can be a challenge to detect
in city telescopes. A couple of entries
in my observing logbook from 20 years
ago illustrate the difﬁculty and reward
of ﬁshing for faint fuzzies in a lightpolluted setting: M1 in Taurus: 4¼Ǝ f/6
Newtonian, 50×: a slightly oval smudge.
100×: a bigger smudge!
The next entry was more detailed:

S ONE TARGET, TWO CLUSTERS The cluster identified as NGC 1746 is likely two clusters
located at different distances. Based partly on
historical observations, the bright, sprawling
western portion of NGC 1746 is also (confusingly) designated NGC 1750, while the faint
eastern portion is sometimes called NGC 1758.

10Ǝ f/5.5 Newtonian, 116×: dim, diffuse,
egg-shaped, oriented NW-SE, brighter at
NW end, dimmer at narrow SE end (facing Zeta). 150×: nebula is a thick, blurry
letter S. No ﬁlters used.

Suburban Treasures in Taurus
Object

Type

Mag(v)

Size/Sep

Dec.

ɇ559

Double star

7.0, 7.0

3.1″

04h 33.5m

+18° 01′

NGC 1647

Open cluster

6.4

45′

04h 45.9m

+19° 06′

04h

45.9m

+19° 10′

AG 311

Double star

8.9, 9.3

33.0″

NGC 1746

Open cluster

05h 03.8m

+23° 46′

AG 313

Double star

9.4, 10.0

19.7″

05h 04.6m

+23° 39′

SNR

8.4

6′ × 4′

05h

34.5m

+22° 01′

Double star

9.0, 9.9

21.7″

05h 36.4m

+21° 11′

4.2″

05h

+22° 00′

M1
ɇ740
ɇ742

Double star

7.1, 7.5

36.4m

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.

For city observers, light-pollution
ﬁlters generally are a boon, but when it
comes to the Crab, the situation is complicated. A broadband light-pollution
ﬁlter or a narrowband Ultra-High Contrast (UHC) ﬁlter boosts the contrast
between M1 and the background sky.
However, the overall view (especially
with a UHC) is darker. And the view in
a doubly ionized oxygen (O III) ﬁlter is
so dim that I don't recommend it. In
fact, I prefer Crab ﬁshing sans ﬁlter. My
8-inch, working unﬁltered at 41×, pleasingly frames Zeta Tauri, a resolved Σ740,
and the pale nebula. Your conditions
might be worse than mine, so I encourage you to experiment with whatever
ﬁlters you have.

January Is Taurus Time
I observed the Crab in the predawn late
in the summer, when Taurus was halfway up the eastern sky. The positioning
was perfect for the motions of my alt-az
Dobsonian. M1 was a vertical hop from
Zeta Tauri, and the clusters between
Aldebaran and Elnath were a low-power
horizontal slide from either star. For
most readers, approximately the same
orientation occurs at nightfall in midJanuary, when there'll be no evening
moonlight to spoil the view.
Eastern Taurus awaits. So, never
mind the city lights - grab the Bull by
the horns the ﬁrst chance you get!
Contributing editor KEN HEWITTWHITE studies the night sky from southwestern British Columbia.

JANUARY 2 021 * SK Y & TELESCOPE

4
5
6
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8
9
10

POSS-II / STSCI / CA LTECH / PA LO M A R OBSERVATORY

NGC 1758?

Star magnitudes

fe
s"
n'

5h 34m

Sky & Telescope - January 2021

Table of Contents for the Digital Edition of Sky & Telescope - January 2021