Impressions of the Southern Sky: Part IV

My last night of astronomy in Chile was the best. It was short
but intense, and utterly magical. I had intentionally saved the
best for last, namely the Carina Milky Way. I had, of course,
seen NGC 3372, the Eta Carina Nebula, several times already by
this point; one can hardly miss it if it is above the horizon.
And I had even taken a few quick peeks with bigger scopes,
knowing that the opportunity would not present itself later.
But I had avoided studying NGC 3372 and the area around it with
my own scope because that made most sense well after the New Moon,
when observing in the evening would be impossible.

I had driven the previous day up to a tiny cabin in the Parque
Nacional Nevado de Tres Cruces, at 3700 meters altitude, at least
50 km from the nearest electrical light. It is a place of unearthly
beauty, next to a lake half water and half salt flat, across from
Cerro Tres Cruces, one of the highest mountains outside of Asia
at 6300 meters, surrounded by great swelling hills of red, green,
and magenta rising to some 5000 meters or higher. It was also
probably the first night that I felt completely at home in Chile.
Elsewhere, I was surrounded by an alien culture, but here, in
the mountains, hours from any other person, surrounded by rock,
sand, and snow, scattered tufts of grass, flamingos and guanacos,
wind, sun during the day and stars at night, I was entirely
comfortable, entirely in my own element.

I went to sleep at sunset and set my alarm for 2 AM. By the time
had gotten dressed, eaten a meager breakfast, and gotten outside,
the Milky Way was well above the eastern horizon. The wind had
died completely overnight (thank heavens!) and the air was so clear
that I felt as though I could reach up and pull the stars down
from the sky.

I had already worked my way down through Puppis and well into Vela
on previous nights, so I started with IC 2391 in southern Vela,
near the border with Carina. This is a curious cluster, very
prominent to the naked eye at mag 2.5, but a little disappointing
through binoculars or telescopes, showing mostly as five very
bright blue stars, quite pretty, but not really enough to add up
to a cluster. From there, I worked my way towards the Eta Carina
area through some minor but attractive open clusters, with a side
trip to the very impressive globular cluster NGC 2808. NGC 2808
reminds me a little of M3; it seems very similar in size and
brightness, and like M3, is only grainy, not truly resolved, in
my 100mm scope. Presumably, a cluster of great intrinsic brightness
at a rather large distance from the Earth.

I ended in the field around the Eta Carina Nebula, which must be
the very richest field in the entire Milky Way, richer even than the
area between M8 and M16. Within a 5-degree radius around Eta Carina
lie no fewer than four prominent naked-eye clusters, a couple dozen
lesser clusters and nebulae, and of course, NGC 3372, the Eta Carina
Nebula itself.

NGC 3372 is the biggest and brightest emission nebula in the sky
by a huge margin. Imagine an area the size of the North America
Nebula and with the surface brightness of M8. When it is above
the horizon, it is by far the most prominent thing in the sky; it
catches the eye immediately. Viewed naked-eye, it is hard to say
exactly where it ends, because it is embedded in an extremely
bright patch of the Milky Way. I wish I had thought to view it
naked-eye through my UHC filter, which would have distinguished
between the nebulosity and the Milky-Way background.

At this time of night, Eta Carina and Orion were both well placed
in the sky, and I found myself comparing the telescopic views of
NGC 3372 to M42, the only serious competitor for the title of
most magnificent object in the sky. On the whole, I must admit
that I still prefer M42, although the comparison seems a little
silly; the attractions of the two nebulae are completely different.
Without a doubt, NGC 3372 is much bigger, much brighter and (I
must admit in all fairness) much more complex. NGC 3372 is
stupendous to the naked eye, while M42 is barely visible. On
the other hand, NGC 3372 is much more uniform in surface
brightness; no part comes even close to the intensity of the
Hughenian region around the Trapezium.

Perhaps the bottom line is that the telescopic view of M42 is
dominated by bright nebulosity, while the telescopic view of
NGC 3372 is dominated by dark nebulosity. Needless to say,
M42 has plenty of dark lanes, but the first impression is the
fantastic brightness of the Hughenian region and the great
sprays of brightness, the wings that stretch out from it.
With NGC 3372, by contrast, the first impression is the great
right-angled dark lane separating the bright area right around
Eta Carina from the larger nebula. Then, at higher power, one
notices the famous Keyhole right next to Eta Carina, and on
further inspection, dark lanes start to show up all over the
nebula, especially with the aid of a narrowband filter.

The central stars of the two nebulae could also hardly be more
different. The Trapezium is dazzling blue, and Eta Carina is
dull brown, a truly bizarre color for a star. The reason is
plain at high power; Eta Carina is entirely cocooned by the
miniscule, wrinkled Homunculus Nebula.

The area around NGC 3372 is full of clusters and nebulae, but the
four most remarkable are the bright naked-eye clusters NGC 3114,
NGC 3293, NGC 3532, and IC 2602. Of those, I probably like IC 2602
the least; in my estimation, it does not live up to its nickname
of the Southern Pleiades. It is bright to be sure, mag 1.9 as
compared to 1.2 for the Pleiades. But far too much of that light
is contained in the single star Theta Carina (mag 2.7); it is a
2-magnitude jump down to the next three stars, and one of those
is so close to Theta that I cannot separate it by naked eye.
Compare that to Pleiades, where the six brightest stars span only
1.5 magnitudes, and all six can be separated easily by naked eye.
Consequently, my naked-eye impression of the Pleiades is of
a cluster, even under heavy light pollution, whereas my impression
of IC 2602 is of one bright star with one or two faint companions,
even under pristine skies. IC 2602 does much better through
binoculars or a telescope, but it is still cannot compete with
M45 either in richness or in the elegance of its shape. However,
IC 2602 does have one uniquely charming feature. Right on its
edge is another cluster, Melotte 101, which is much smaller and
fainter but also richer and more elegant when viewed through a
telescope. Even when unresolved, as in binoculars, Melotte 101
stands out surprisingly well as a cloud of light.

At roughly mag 4.0, NGC 3114 is fainter than IC 2602, but more
impressive. It shows as a bright but unresolved cloud of light
to the naked eye, is partially resolved in binoculars, and is
glorious at 20X in my 100mm scope. It is consists of some dozen
stars ranging from bright (mag 8) to very bright (mag 6) in a
kind of shock-wave shape facing E backed up by some 50 fainter
stars, all spread out over about 40'. It is not terribly well
defined, being quite loose and set against a very rich background;
nonetheless, it has enough stars to make a very convincing cluster.

NGC 3293 is as tight as NGC 3114 is loose. Wolfgang Steinecke's
Revised NGC list this at 40', but that seems grossly inaccurate
to me. The cluster may have some vestiges out to 40', but the
visual impression is dominated by some dozen bright stars crammed
into a 5' circle, backed up by another dozen or two stars ranging
from faint to moderately bright. The cluster is just loose enough
to be resolved well in binoculars, but it shows to the naked eye
as a slightly fuzzy star.

NGC 3532 is the probably the finest of all the magnificent clusters
in Carina. To the naked eye, it appears as a faintish cloud of
light off to one side of the bright star V382 Carina (mag 3.8 - 4.0).
In my 100mm scope, it appears as a very rich collection of at least
75 stars faint through bright arranged roughly in the shape of a
parallelogram about 40' by 20'. It is dense enough to stand out
well despite the fact that the background is extremely rich.

- Tony Flanders

Beautiful writing, thanks for sharing this. Now I have to reload the
entire list to catch Parts 1-3.

Being a relative newbie with only three years under my belt, of course
I wish to know how you experienced observing Omega Centauri, 47
Tucanae, and the Magellanic Clouds... I am so shallow.

- Livingston

On 11/11/03 20:58 +0900, Tony Flanders wrote:

[ snip ]

Great report. I concur with earlier comments that you should
seriously consider submitting these articles to S&T or Astronomy.

trane
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