SKY_September2014.pdf

OBSERVING

Deep-Sky Wonders

58 September 2014 sky & telescope

In 1804 Giuseppe Piazzi deduced the large proper

motion of 61 Cygni from previous observations made by

himself and others, and he cataloged the results two years

later. In 1838 Friedrich Wilhelm Bessel calculated the

distance to 61 Cygni based on precise measurements of

the star’s parallax — the shift in its apparent position due

to Earth’s changing perspective as it orbits the Sun. That

was the fi rst accurate measurement of the distance to any

object outside our solar system.

Through my 130-mm scope at 23×, 61 Cygni’s primary

star appears deep gold, and its modestly fainter compan-

ion to the south-southeast looks a bit more orange to me.

In reality, the two stars have nearly the same spectral

type, the brighter one K5 and the dimmer one K7, which

weigh in at three-fourths and one-half the mass of our

Sun, respectively. What colors do you see?

Climbing 2.4°° north from Sigma (σ) Cygni we come

to the exceptionally ancient open cluster Berkeley 56. A

2011 Astronomical Journal paper by Kenneth A. Janes and

Sadia Hoq puts it at 6 billion years old and 36,000 light-

years away from us.

Through my 10-inch refl ector at 43×, Berkeley 56 is a

faint, grainy powder. Two stars closely guard its northwest

quadrant, magnitudes 10.5 and 12.3. Perched north of the

This photomosaic makes it clear why the North America Nebula

got its name. The Pelican Nebula, to its right, is harder to make

out because the deep exposure tends to fi ll in the dark nebula

that divides the beak from the body. IC 5068 is the tripartite

nebula below the Pelican

ROBERT GENDLER

6884

Alessi-Teutsch 11

6856

Berk 56

_ b

a

i

m

o

t^1

k^1

t^2

k^2

s

20

23

30

33

61

Deneb

6866

6910

M29

7039

7044

7062

7086

8

6888

IC 5068

6826

7008

7027

7048

+55°

21 h 00 m 20 h 30 m 20 h 00 m 19 h 30 m

+50°

+45°

+40°

26

Pelican

Nebula

North America

Nebula (7000)

j (IC 5070)

Star magnitudes

2

7

3

4

5

6

cluster, a distinctive pattern of fi ve 9th- to 12th-magnitude

stars forms a slender V that has slightly curved sides and

points northwest. At 115× four stars arc across the haze,

two in the south-southwestern edge, one at the center,

and one in the northern edge. At 213× several extremely

faint stars dot the haze, but these are probably in the

foreground. The brightest possible cluster member listed

by Janes and Hoq is magnitude 14.3, and the rest are mag-

nitude 15.6 and fainter.

Berkeley 56 is exceedingly rich in stars, otherwise it

wouldn’t have been able to hold itself together for such a

long time. Janes and Hoq catalog 997 possible members,

most well beyond the reach of amateur telescopes. How

many stars can those of you with very large scopes pry out

of the haze? ✦

DSW layout.indd 58 6/23/14 12:17 PM