Sky & Telescope - May 2021 - 55

Attractive Opposites
In my 10-inch f/6 Dobsonian, a wideangle 30-mm eyepiece producing 50×
frames the galaxy pair with room
to spare. The targets are delightfully
unalike. M82, aptly named the Cigar
Galaxy, is a strongly elongated, patchy
nebulosity of modest central concentration. In contrast, M81 is a diffuse oval
brightening smoothly toward its core.
Tripling the magnification and
focusing on M81's center, I glimpse
a teeny nucleus. Cupping my hands
around the eyepiece and employing
averted vision, I see that M81's elliptical halo is oriented north-northwest by
south-southeast. On the latter side, the
tenuous mist extends a few arcminutes
to a couple of 11th-magnitude stars
85″ apart. Images show the spiral arms
curling beyond those stars. Alas, the
armless " nebula " in my 10-inch Dobsonian is reduced to a breadth of 8′ or 9′

13h

Star magnitudes

drab suburban sky. So, I guestimate its
location. Eventually, my finderscope
snares it, along with 5.7-magnitude
HD 83489 one degree to the southeast.
After centering HD 83489 in a lowpower eyepiece, I head eastward another
degree to the Bode lode.
I prefer the roundabout but surefire
star-hop promoted by former S&T senior
editor Joshua Roth. Following Josh's
advice, I cast my gaze west of the Dipper
to 3.4-magnitude Omicron (ο) UMa,
which mark's the Great Bear's nose.
From Omicron, I turn northeastward
and make a series of four-degree hops
- first to a shallow triangle of 5th-magnitude stars that includes Pi1, Pi2 (π1+2)
and 2 UMa; then to a similarly bright
isosceles triangle consisting of Sigma1,
Sigma2 (σ1+2), and Rho (ρ) UMa; and
finally to 24 Uma where a right-angle
turn finds HD 83489 and the galaxies.
Circuitous, yes, but safe.

12h

κ

10h

λ

DRACO

2
3
4
5
6
7
8

11h

9h

8h

24

M82

σ2

M81

ρ

+65°

π1 2

σ1

π2
τ

ο
+60°

α
M40

Dubhe

δ
Megrez

υ
Merak

γ
M109

Phecda

M97

+55°

β

M108

URSA MAJOR
φ

θ

+50°

S IN THE BEAR'S DEN Two separate star-hops lead from the Big Dipper to the Big Bear pair. The
most direct route involves a veering line from Phecda to Dubhe and on to the key 5th-magnitude
star 24 Ursae Majoris. Longer, but easier to follow with optical finderscopes, is the multi-asterism
star-hop from 3rd-magnitude Omicron Ursae Majoris, described in the text.

- barely a third of its photographic size.
Score one for the city lights.
Two more dots aligned north-south,
135″ apart, lie 10′ south-southwest of
the galaxy. Each dot is a double star. The
northern duo, Σ1387, comprises identi-

cal 10.7-magnitude components 9.0″
apart; Σ1386 has 9.3-magnitude twins
separated by 2.2″. The wider set is easy,
and the tighter tandem splits cleanly
in a 9-mm eyepiece yielding 169×. I've
studied M81 for decades, not noticing

24
M82

M81
Σ1400
3077

HD 83489

Σ1387
Σ1386

Σ1398

SE AN WA LK ER

X BODE'S NEBULAE Discovered by Johann
Bode in 1774, these dominant members of the
M81 Group are separated by about one million
light-years. During a sideswipe a few hundred
million years ago, larger M81 severely distorted
smaller M82. Lesser members NGC 3077 and
NGC 2976 also participate in this slow but
dangerous cosmic dance.

2976

s k y a n d t e l e s c o p e . o r g * M AY 2 0 2 1

55


http://www.skyandtelescope.org

Sky & Telescope - May 2021

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

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