Sky and Telescope - May 2018 - 25

So without further ado, let's explore some of the Big, Bold,
Bright, and Beautiful objects in the spring sky.
Let's start in the north. All the way north, in fact.
Polaris, Alpha (α) Ursae Majoris, is the North Star, around
which all the other stars in the sky appear to revolve. That
in itself would make it worth looking at, for the concept
if nothing else, but Polaris is intrinsically interesting and
would be worth a look no matter where in the sky it might
be. Why? Because it's a double star. And it's not just any
old double; it's a wildly unequal double, with a primary
of magnitude 2.0 and a secondary of magnitude 9.0. Each
magnitude of difference is about 2.5 times brighter than
the next, so that means the primary is 2.5 to the 7th power
(their difference in magnitude) or 610 times brighter than
the secondary.
Brightness differences that extreme normally make the
secondary star hard to see. (We talk about doubles being
"hard to split" if their separate components are difﬁcult to
distinguish.) Fortunately Polaris's companion lies 19″ away,
which is far enough to let the secondary stand out beyond the
primary's glare, yet close enough to make the pair interesting. You should be able to see it with a good 3-inch or larger
telescope. If not, it might be masked by a diffraction spike.
Try rotating the scope or waiting a few hours. Polaris will still
be right where you left it.

The secondary is an actual companion, albeit a distant
one. Its true separation has been estimated at 2,400 astronomical units from the primary and its period at 42,000
years. It will be a long time before you notice any movement.
Skipping over the various Messier objects in Ursa Major
(although you would be foolish to do so on a tourist outing),
I'll move on to the star Y Canum Venaticorum, known as La
Superba. It's inside the curve of the Big Dipper's handle,
right about where the point of your compass would go if you
were to extend the handle around in a circle. La Superba is a
carbon star, which means it's one of the deepest red stars in
the sky. At an average magnitude of 5.3 you can see it directly
under dark sky, but you probably won't notice its color until
you look at it through binoculars or a telescope. When you
collect enough light, you'll trigger your color vision and suddenly you're looking at a glowing barbecue coal.
Seriously, that's about what you're looking at. Carbon stars
are so cool that carbon soot collects in their atmospheres and
scatters most of the blue light, leaving only the red charcoal
glow to escape the photosphere and travel to your eye.
Like many carbon stars, La Superba is variable, ranging
from 4.8 to 6.4 with a period of about 157 days. The intensity
of its color changes with its overall brightness, so check this
one often and see if you can ﬁgure out when it's brightest,
and when it's reddest.

Where to Find the Big, Bold, Bright, and Beautiful
Object

Designation

Type

Surface
Brightness

Mag(v)

Size/Sep

RA

Dec.

Polaris

Alpha UMi

Double star

-

2.0, 9.0

-

02h 31.8m

89° 16′

12h

La Superba

45.1m

45° 26′

Y CVn

Carbon star

-

4.9

-

Whale Galaxy

NGC 4631

Galaxy

12.8

9.2

12.8′ × 2.4′

12h 42.1m

32° 32′

Hockey Stick

NGC 4656

Galaxy

13.5

10.5

10.0′ × 1.8′

12h 43.9m

32° 09′

12h

NGC 4657
Melotte 111
Needle Galaxy

NGC 4565

Lalande 21185
Leo Triplet

M95

M65

Galaxy

10.5

10.9

1.3′ × 0.6′

Open cluster

-

1.8

300′

12h 25.1m

26° 07′

Galaxy

13.2

9.6

15.8′ × 2.1′

12h 36.4m

25° 59′

11h

03.3m

35° 58′

44.2m

32° 12′

Red dwarf star

-

7.5

-

Galaxy

12.8

9.3

9.8′ × 2.9′

11h 18.9m

13° 06′

20.3m

12° 59′

M66

Galaxy

12.7

8.9

9.1′ × 4.2′

11h

NGC 3628

Galaxy

13.4

9.5

14.8′ × 3.0′

11h 20.3m

13° 35′

9.7

7.4′ × 5.0′

10h

44.0m

11° 42′

46.8m

11° 49′

Galaxy

13.5

M96

Galaxy

13.1

9.3

7.6′ × 5.2′

10h

M105

Galaxy

12.8

9.3

5.4′ × 4.8′

10h 47.8m

12° 35′

NGC 3384

Galaxy

12.6

9.9

5.5′ × 2.5′

10h 48.3m

12° 38′

NGC 3389

Galaxy

13.2

11.9

2.8′ × 1.3′

10h 48.5m

12° 32′

Rinnan's Run

Asterism

-

6.1-13+

-

10h

46.5m

3° 20′

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.

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Sky and Telescope - May 2018

Table of Contents for the Digital Edition of Sky and Telescope - May 2018
