The Caldwell Objects

NGC 7331 is extended much farther to the south
than to the north, possibly indicating an
interaction between NGC 7331 and at least one
member of the Quintet. The Quintet's brightest
member, NGC 7320 (magnitude 12.7), has a
relatively small recession velocity of 786 km per
second — a value rather similar to NGC 733l's;
the other four galaxies (three of which display
signs of strong tidal interaction) all have redshifts
ranging from 5,700 to 6,800 km per second. Since
recession velocity, or redshift, is proportional to
distance in the Big Bang worldview, it appears
that NGC 7320 is a foreground object that just
happens to lie in the same direction as the other
Quintet members. However, a small but vocal
minority of researchers holds that redshift and
distance may be unrelated in at least some cases,
and they believe that NGC 7320 is physically
associated with the rest of Stephan's Quintet.
Stephan's Quintet is also famous in another
"heavenly" way. Woodruff T. Sullivan III
explained this in the January 1997 issue of Sky &
Telescope:
In the well-known 1946 film It's a Wonderful
Life the opening sequence involves a con-
versation between angels, who are represented
as galaxies in the sky. Only on my latest (nth!)
viewing of this film did I notice that the
pictured galaxies greatly resembled
Stephan's Quintet __ After some checking
I discovered that the filmmakers indeed used a
photograph of Stephan's Quintet, with NGC
7320 (first angel) talking to NGC 7318A and Β
(second angel). They were later joined by Angel
Second Class Clarence, who is portrayed only
as a foreground star, perhaps due to the
difference in rank.
The Caldwell Objects
As Sullivan suggests, it is only appropriate that
Clarence is not portrayed as a galaxy in this
opening scene, for he had not yet earned his
wings, which are obviously interpreted as the
swooping, winglike spiral arms surrounding the
"bodies" of the high-ranking angels. Luginbuhl
and Skiff note that "with care, a 6-inch will show
four of the [Quintet's] members, but it takes a 30-
centimeter to show the fifth (NGC 7319;
magnitude 13.1) even faintly." NGC 7319 has
what astronomers call a Type 2 Seyfert nucleus
(see Caldwell 24).
30
By the way, teachers, street-corner astron-
omers, and public-observing-session hosts might
consider using Pegasus and its celestial delights
to illustrate the night sky's utility as a time
machine. Start with the four stars marking the
corners of the Great Square of Pegasus: Markab
(140 light-years distant), Alpheratz (97), Scheat
(199), andAlgenib (333). Next turn your telescope
15° north of the Square until you reach Caldwell
22, the bright planetary nebula NGC 7662 (3,200
light-years); this object could lead into a
discussion of stellar evolution. The famous
globular cluster M15 (31,000 light-years), 4°
northwest of Enif, would then transport your
audience out to the halo of our Milky Way
galaxy. A tap of the tube could then take
bystanders nearly 47 million light-years farther,
to NGC 7331. NGC 7331 can also be fruitfully
compared with M31, which equals NGC 7331 in
size and mass but is 20 times closer to Earth. And
finally, if your telescope is large enough to
provide a decent view of Stephan's Quintet, you
can then carry your guests back nearly 300
million years in time, discuss galaxy clusters,
and, of course, talk about It's a Wonderful Life.
121