Sky & Telescope - April 2020 - 54

APRIL 2020 OBSERVING
Deep-Sky Wonders by Sue French
t NGC 3115 is a classic example of a lenticu-

Sextans Uraniae
This obscure constellation is swarming with galaxies.

I

n 1679 a disastrous ﬁre swept through
the estate of renowned Danzig
astronomer Johannes Hevelius. His
home and observatory, Stellaburgum,
burned to the ground. Most of his
books and records were consumed by
ﬂames, and none of his ﬁne instruments survived - including his prized
six-foot brass sextant for measuring
the angular separation between stars.
Hevelius immortalized his lost sextant
by creating the constellation Sextans
Uraniae between astrologically ﬁery Leo
and Hydra. It endures today under the
shortened name Sextans.
Sextans plays host to many galax7RFHOHEUDWH\HDUVRI6XH)UHQFK˪V
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54

APRIL 2 02 0 * SK Y & TELESCOPE

ies, and we're going to visit a sample
of them, limiting ourselves to galaxies
brighter than visual magnitude 12.0. If
you think that means they'll all be easy,
you're mistaken. You'll soon ﬁnd that
a galaxy's magnitude doesn't tell the
whole story.
We'll start with NGC 3115, a large
lenticular (lens-shaped) galaxy about
34 million light-years away with a black
hole a billion times the mass of our Sun
lurking in its heart. It's the brightest
galaxy in Sextans at magnitude 8.9.
NGC 3115 sits halfway between the
5th-magnitude stars Gamma (γ) and
Epsilon (ε) Sextantis and 22′ north of
an imaginary line connecting them.
Even at 23× through my 130-mm (5.1inch) refractor, the galaxy is a bright
oval that greatly intensiﬁes toward the
center. Three times longer than wide,
it lives up to its nickname, the Spindle
Galaxy. The size is easier to estimate
at 117×, appearing approximately 4½′

× 1½′ to my eye. It leans northeast and
holds a small round nucleus. In my
10-inch reﬂector at 171×, NGC 3115 is
5′ long with its tips gradually blending
into the background. A thin core about
2′ long brightens toward the nucleus,
and the halo has a faint star superposed
south of the galaxy's center.
The interacting spirals NGC 3169
and NGC 3166 are twice as distant as
the Spindle and weigh in at magnitudes
10.2 and 10.4. To locate them, aim for
a 25′ asterism of several 7th- to 12thmagnitude stars (pictured in sketch
below right) that makes an isosceles
triangle with Alpha (α) and Beta (β)
Sextantis. To me, the group resembles
the lowercase Greek letter nu (ν) with a
tipped capital delta (Δ) to its west. The
galaxies ﬂoat 12′ north of the ν.
The asterism is mirror-reversed in
my 130-mm refractor but still quite distinctive. Both galaxies are small ovals
with bright cores at 23×. NGC 3169
leans northeast, and NGC 3166 reclines
east-west. At 117×, an 11th-magnitude
star hugs the ﬂank of NGC 3169, east of
center. The galaxy appears roughly 3½′
× 1½′, and its core is oval. NGC 3166
is similar in size but has a rounder and
brighter core. My 10-inch scope at 171×
bestows a stellar nucleus.
On the way to our next galaxy, let's
stop to admire 35 Sextantis. Through
my 130-mm scope at 37×, it's a lovely
double with a yellow-orange 6thmagnitude star nuzzling a deep-yellow
companion to the west-southwest. They
occupy the northeastern corner of an
8′ trapezoid formed with three ﬁeld
stars. A recent spectroscopic study indicates that the companion is composed
of two stars in such close embrace that
they cannot be seen separately through
a telescope.
35 Sextantis heads a remarkable line
of stars that has caught the attention
of various people over the years. With
a slight kink in the top, the sparkling
cascade tumbles south-southeast from
35 Sextantis for 3°. Eugene (Oregon)

DA NIEL V ERSCHATSE

lar galaxy - flattened like a spiral galaxy but
amorphous like an elliptical.
Sky & Telescope - April 2020

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