Sky and Telescope - April 2015 - 58

OBSERVING

Deep-Sky Wonders
14h 00m

13h 30m

13h 00m

12h 30m

12h 00m

Y CVn

Y CVn is the second-brightest carbon star, topped only
by autumn's 19 Piscium (TX Psc). In fact, both stars are
variable with almost the same maximum brightness,
so you could arguably say they vie for ﬁrst place. Y CVn
is a pulsating star that slowly expands and contracts.
Although you can usually spot it in a dark sky, you'll need
binoculars or a telescope to enjoy its color. Carbon stars
are red giants with atmospheres rich in carbon-bearing
molecules that absorb blue light, making them look redder than ordinary giants. If you have trouble seeing color
in the stars, this is deﬁnitely one for you to try.
My globular cluster of choice is Messier 3. Through
my 18×50 image-stabilized binoculars, M3 is ensconced
in a right triangle of stars. The cluster displays a moderately faint halo about 10′ across that looks a bit grainy. The
globe becomes suddenly brighter about halfway in, then
intensiﬁes dramatically toward the center, where dwells
a brilliant point of light. In my 130-mm refractor at 48×,
this beautiful cluster spans about 15′. The halo is resolved
into stars, and the outer core appears partly resolved. At
117× the outer halo seems loosely populated, while the
inner halo and outer core wear a sprinkling of somewhat
brighter stars over a fainter mob. The core is a blaze that
brightens toward the center, and it's accented with several
star-specks competing with its glare.
M3 holds a whopping 300,000 stars and lives 33,000
light-years away from us.
For an open cluster, I've chosen the Coma Star Cluster (Melotte 111). How can you beat a cluster that's as big
across as 10 full Moons? Looking up on a nice night, I
can see about 10 stars, and there's a vague impression of
fuzziness in the area. Observers under dark skies have
reported seeing two dozen stars. Few telescopes can
encompass the entire cluster, so this is one for binoculars.
Through my 10×30 image-stabilized binoculars, most of

Star magnitudes

β
α

2
3
4
5
6

CANES VENATICI

+30°

Con

Type

Mag(v)

τ
υ

the bright stars seem to outline a fancy vase with inwardly
curved sides. The main body sports about 20 bright and
30 dimmer stars, while a sparse area south of the vase
adds 5 bright and 15 faint suns. The brightest gem within
the apparent boundaries of the cluster is golden Gamma
(γ) Comae in the far-northern reaches of the cluster, but
it's actually a foreground star. Can you see color in any of
the other stars?
If you're now asking "Why didn't she choose...?", tell
me about your nominees and perhaps we can do this
again next year. ✦

Size/Sep

Dec.

UMa

Spiral galaxy

6.9

26.9′ × 14.1′

M82

UMa

Starburst galaxy

8.4

11.2′ × 4.3′

9h 55.9m

+69° 41′

M97

UMa

Planetary nebula

9.9

3.5′

11h 14.8m

+55° 01′

14.4″/11.8′

13h

23.9m

+54° 56′

4.9-5.9

12h

45.1m

+45° 26′

Double star

2.2, 3.9/4.0

55.6m

+69° 04′

Y CVn

CVn

Carbon star

CVn

Globular cluster

6.2

18′

13h 42.2m

+28° 23′

Coma Star Cluster

Com

Open cluster

1.8

5°

12h 25.1m

+26° 07′

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.

April 2015 sky & telescope

+20°

M81

UMa

COMA BERENICES

Mizar/Alcor

β
Coma Star
Cluster

Sue's Spring Hits
Object

+40°

When viewed
through 18×50
image-stabilized
binoculars, M3
resolved to a
brilliant point of
light, surrounded
by a grainy halo.

Sky and Telescope - April 2015

Table of Contents for the Digital Edition of Sky and Telescope - April 2015