OF THE ROGER N. CLARK

VISUAL ASTRONOMY OF THE DEEP SKY
A VISUAL ATLAS OF DEEP-SKY OBJECTS
NGC 7662, PLANETARY NEBULA IN
ANDROMEDA
R.A. 23h 25.9m, Dec. 42° 33' (2000.0)
Technical. NGC 7662 is a small planetary
nebula somewhere between 2000 and 6000
light-years away. (The distances of all planetary
nebulae are poorly known.) Its diameter
is between 0.3 and 0.8 light-years, depending
on the distance adopted. The central star has
a surface temperature around 75 000 Kelvin
and has been suspected of variability, though
no systematic photometric study has been
completed. The nebula consists of an inner,
broken ellipse surrounded by a fainter elliptical
disk. The dark area in the center is
perhaps similar in brightness to the outer
ellipse.
--
Visual. NGC 7662 has a total magnitude of
8.5 and an angular size of 32 by 28 arc.
seconds, for a very high mean surface bright.
ness: 15.6 magnitudes per square arc-second
The planetary is visible in 7 X 50 binocula
and small telescopes as a star, but will begin
to show its disk at powers near 50 X. Through
the 8-inch telescope under moderate skies
the darker center was suspected at 334x and
seen fairly well at 592 X.
This object provides a good example of
how the upper limit to useful magnification
depends on image brightness. In the dim
light levels of deep-sky astronomy, the eye
has very poor resolution, so small detail may
have to be magnified very highly to be detect.
able. The 8-inch had no clock drive for tracking,
so examination of this object was rather
difficult at very high powers. Telescopes of
similar size with clock drives could use higher
powers still. The lesson is that if you are
observing an object and feel that higher magnification
may bring out more detail, go
ahead and ignore the "accepted" magnification
limit of 60 X per inch of objective diameter
(480X on an 8-inch telescope) . See
Chapter 3 for more on this subject.
Photograph of NGC 7662. South is up . (Courtesy
Jack B. Marling.)
---1' ---
Drawing of NGC 7662.
Scale: 0.25 arc-min/cm
8-inch fll l.5 Cassegrain
12.4mm Erfle (188X)
7mm Erfle (334x)
l2.4mm Erfle + 3. l5x
barlow (592X)
Viewing Distance (cm)
50X:275 300X:46
IOOX: 138 400x:34
200x: 69 600x:23
air mass: l.41, faintest star: 13.8 at zenith, 188x;
no tracking
9/5/83 14:00- 1 4:20 UT at Hawaii Kai, Hawaii; R.
Clark
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