Sky & Telescope - February 2021 - 30

Winter Deep Sky

6.9-magnitude HD 40981, then turned eastward to 7.1-magnitude HD 41657, and ﬁ nally southeastward to 7.6-magnitude HD 42088, which, according to the Uranometria, sits
inside the nebula.
Observing at 64×, I detected no nebulosity until I applied
an Ultra-High Contrast (UHC) narrowband ﬁlter. Bingo! A
tenuous, spherical haze, perhaps ¼° in diameter, magically
materialized around HD 42088. (Focusing on stars of similar
magnitude conﬁrmed I was experiencing nebulosity, not
eyepiece fog.) A doubly ionized oxygen (O III) ﬁlter provided
excellent contrast - the round haze was unmistakable -
but the O III ﬁeld at higher magniﬁcations was a bit dark. A
broadband light-pollution ﬁlter proved only marginally helpT THE NUMBER CLUSTER Roughly 3,000 light-years distant, thinly
populated, and distinctly odd-looking, NGC 2169 has been dubbed the
37 Cluster due to its appearance in an upright (not inverted or mirrorreversed) telescope field. The numerical name was coined by Kentucky
amateur Alan Goldstein in 1981. Light-hearted observers also picture
NGC 2169 as the Shopping Cart Cluster. Can you configure a cart in
these stars?

NGC 2169

ful at any magniﬁcation. Of the various combinations I tried,
the winner was the UHC used at low power.
The above combo in place, I noticed a 10′-long, sevenstar asterism (evidence of Collinder 84?) stretching northeastward out of the spherical haze. I dumped the ﬁlter and
bumped up the power. Aha! To my eye, the pattern resembled
the Big Dipper. HD 42088, mentioned earlier, plays the role
of Alkaid (η Ursae Majoris) at the end of the handle. A dimmer star is Mizar (ζ UMa). A nicely balanced, 10.6-magnitude
double, 24.8″ wide, called SCA 37, is Alioth (ε UMa). A star
corresponding to Phad (γ UMa) in the bowl is SCA 36, an
unequal binary whose 10.3- and 12.8-magnitude components, 13.5″ apart, split beautifully at 218×.
I was intrigued by a cluster, which the Uranometria labels
NGC 2175.1, on the eastern edge of the nebula. In their
authoritative book Star Clusters, Brent Archinal and Steven
Hynes caution that the identiﬁer 2175.1 is not original to the
NGC catalogue; " where possible this cluster should probably
be referred to as C0607+206. " Fine by me - I just wanted to
know if the plotted object would appear in my scope.
Hardly 5′ across, C0607+206 lies 2′ northwest of the
9.2-magnitude star HD 42333. I had no difﬁculty ﬁnding
HD 42333 because " the pointers " in the mini-Dipper aim
right at it. In the Dob at 169×, the cluster yielded a row
of four stars northward, plus a clumping southward. The clump possesses one bright star. It's a
binary, listed as J 1922, featuring 10.5- and
10.9-magnitude pinpricks 6.6″ apart. Cracking that nut at 218× was super satisfying.

Struve 848

FEBRUARY 2 021 * SK Y & TELESCOPE

Finally, I pushed farthest north, to
the top of the Hunter's club, where
the cluster Basel 11b resides near
Orion's border with Gemini. My
star-hop to the 8.9-magnitude
target again involved increasingly
fainter steppingstones, this time
beginning at 4.2-magnitude 1
Geminorum. From there, I swept
past the 6.4-magnitude variable
star HD 40724, to 6.9-magnitude
HD 40443 in Orion. Immediately
northwest of HD 40443, an equilateral triangle of 9th-magnitude stars
led me to 3′-wide Basel 11b further on.
Amazingly, the little blighter showed in
my Newtonian at 64×.
That said, Bas 11b at 64× was a mush of
12th-magnitude suns forming a southwardaiming arrowhead. Powering up to 218× resolved
the mush into a short row of three stars, plus a
fourth farther out, and a ﬁfth at a sharp angle to
the row-of-four. Woohoo! Somehow, the arrowhead had
morphed into a hockey stick. (As a winter-ravaged Canadian,

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

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Sky & Telescope - February 2021

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