Australian Sky & Telescope — January 01, 2018

60 AUSTRALIAN SKY & TELESCOPE January 2018

MILKY WAY: JEREMY PEREZ; NGC 2360: JIM THOMMES

has as many descriptions as there are observers. I see a

spray of bright stars like a sheaf of grain, and in Deep-Sky

Companions: The Caldwell Objects, Stephen James O’Meara

compares it to a butterfly’s chrysalis. Have a look and see

what you think.

From NGC 2360, sweep north-northwest 5.5° to find a

nice pair of open clusters, NGC 2343 and NGC 2353, sitting

just over the border in the constellation Monoceros. Both are

embedded in a vaguely bat-shaped asterism of half a dozen

fifth- and sixth-magnitude stars. Those bright foreground

stars are O, B and K giants, ranging from 400 to 1,900 light-

years distant — practically next door in galactic terms. NGC

2343 and NGC 2353 are much farther out, at 3,400 light-

years, where our own Orion Spur points toward the Perseus

Arm of the Milky Way. NGC 2343 has a distinctive shape like

a miniature Hyades cluster, with the part of Aldebaran played

by the red giant star HD 54387.

Another 3° north-northwest of NGC 2343 lies M50.

Considered on its own, M50 is one of the lesser Messiers,

unlikely to make anyone’s list of favourites. But you really

have to work to consider M50 on its own, because this field

is so rich. Any 50- to 70-mm binocular will show M50 in

the same field with NGC 2343 and 2353, against a starfield

so dense that it’s hard to tell where the clusters end. The

question of which stars do and do not belong to these

clusters is a real problem for professional astronomers, but

for amateur stargazers it’s no problem at all. We only need to

look and enjoy.

Sweep about 10° west of M50 and you’ll find a triangle of

bright stars — Beta (β), Gamma (γ) and 7 Monocerotis. Beta

Monocerotis is a famous triple star, and well worth revisiting

at higher magnification, but it also forms a nice binocular

double with HD 45709, which lies 4′ to the northwest. At the

southern point of the triangle, 7 Monocerotis and HD 44178

make an even easier split, with a separation of 6.4′.

Nestled within this triangle you’ll find NGC 2215.

This cluster is probably the toughest catch so far on the tour.

I’ve spotted it through a 9×50 finder, but only under very

dark skies. Any instrument of 70 mm or larger should reel

it in, though, revealing between a dozen and 20 equally

bright members. Checking my logbook, I see that at different

times I’ve compared the curving star chains of NGC 2215

to a fleur-de-lis and, well, a pumpkin. The flower is a much

more elegant metaphor, so let’s go with that.

Two degrees north of Beta Monocerotis lies NGC 2232.

This cluster is one of my favourites. Anchored on 10

Monocerotis and with three lobes of bright stars spanning

almost 1°, it’s big and bright enough to have easily been a

Messier object, if only Messier had spotted it. The cluster’s

prominence is a function of its proximity — at only 1,300

light-years, it’s slightly closer to us than the Orion Nebula.

Our next ‘object’ has no name, but it may be the best view

in the entire tour. Five degrees north of NGC 2232, you’ll

find an arc of bright stars straddling the celestial equator.

NGC 2360

Summer Milky Way

(^1) Caroline Herschel discovered open cluster NGC 2360 in 1783 with
her “comet sweeper,” a small telescope with 14½× magnification with
a 3° 10 v field of view.
SWhen we look at the Milky Way during the summer months, we’re
looking away from the center of our galaxy, so it appears fainter than
it does in the winter in similarly dark conditions. Even so, it still holds
many spectacular deep sky objects.
BINOCULAR TOUR