The Caldwell Objects

W. Sinnott's NGC 2000.0 has a visual magnitude
of 10.7 for NGC 4038 and a photographic
magnitude of 13 for the dim southern component.
I estimated NGC 4039's visual magnitude to
be in the ballpark of 11.2.
The overall view of the galaxy pair is best at
72x, because higher powers tend to overly spread
out the light of this already diffuse object. This
also explains why the Ringtail is such a poor
sight from suburban locations; add light to the
sky background and the galaxy pair simply fades
from view. At 72x NGC 4038 looks like a clumpy
wad of tissue, while NGC 4039 looks more like a
tapered haze. The dark 1'-wide wedge of space
separating the two components is exceptionally
clear at this power. Try focusing your attention
on the fainter member of the duo. Can you see
that it, too, is not a uniform mass of light?
Together the interacting spirals look like curdled
milk stirred into coffee. Every now and again, I
did suspect that I was seeing the southeastern
section of the tidal tail. If the 4-inch at an altitude
of 4,200 feet does indeed perform like a 10-inch at
sea level, then I might not have been imagining
it, for Houston says he could "easily see" the tail
in a 10-inch reflector from Omaha, Nebraska.
Using high power on one exceptionally clear and
transparent night, I resolved the northwestern
component's entire rim into a circle of knotty
clumps; the most prominent one matches the
location of the "barred spiral" cluster mentioned
above. What a glorious moment, to be able to see
traces of extragalactic star formation that has
been in progress for perhaps only a million years.
If we accept the distance to this galaxy pair
as 83 million light-years, then NGC 4038 has a
linear diameter of 270,000 light-years (30,000
light-years broader than NGC 4039) and a
luminosity of 40 billion Suns. We see NGC 4038
inclined 27° from edge-on, and the
60 & 61
duo is receding from us at a speed of 1,640 km
per second. The systems belong to the Corvus
Cloud of galaxies, which has 63 members with
known redshifts.
As alluded to above, the NGC 4038-39 duo
has several common names, the most popular
being the Ringtail (or Rattail) Galaxy and the Antennae.
But one could think of others. Houston
saw the two interacting galaxies as an apostrophe,
or the "mother of all water fleas." Ron
Morales envisioned them as shrimp. Luginbuhl
and Skiff called the pair a cashew, while Tom
Lorenzin saw it as a comma. I thought it looked
like the Greek lowercase letter Nu (ν) on its side.
And John Sanford says the galaxies look like a
doughnut with a bite taken out of it. See if you
can come up with your own imaginative
moniker.
One final thought. If anyone questions that
observing is a visual sport, or that you can better
your visual threshold, consider the following
account. When I first attended the Texas Star
Party (TSP) in 1986,1 was more of a skilled
planetary observer than a deep-sky observer. One
night Larry Mitchell showed me NGC 4676A and
NGC 4676B (The Mice), an interacting pair of
galaxies in Coma Berenices, through his 24-inch
reflector. The Mice are similar to the Antennae,
but they are fainter (13th magnitude each), and
their tails are much harder to see — especially the
southern one. "See the tails?" Mitchell asked me
on that particular night. "Yup," I replied, "I see
one bright one." "But do you see the tail?" Try as I
might, I couldn't. He laughed, and said, with an
exaggerated Texan drawl. "Weeelll, Stephen,
don't worry, we're going to make you a deep-sky
observer yet." I continued to attend the TSP on
and off over the next 13 years. Each year, I would
observe, listen, and learn from Mitchell, Barbara
Wilson, Brian Skiff, and many other great deepsky
observers. I began to view these
The Caldwell Objects 243