Opus Observes: Back in the Spring of Things

It's been a while since I posted one of these things.

2:50 a.m. 25 April 2004 PDT (2004-04-25-0950 UT)

That date is not a typo. My time outside with Opus has been limited
quite a bit lately, mostly because of the kids, but also because the
usual California "June Gloom" came by a few months early this year.
But that seems to have passed us by for the moment (knock on wood,
plastic, multi-coated optics, anything I can get my hands on). I had
to sit with the younger one to get him to go to bed, and unfortunately,
his bed is so comfortable that I went ahead and fell asleep, too.

It was about 2:15 before I woke up again. I immediately considered
going out for a session, but I wasn't sure my body was up to it. I
read my e-mail and news as a temporizing measure, and by the time I
finished (putting in a fairly lengthy post, as I recall), I was
sufficiently energized to dig out the stuff.

It really has been a while. The last time I had actually observed
with the C5+ was about September, when I did an experiment with
simulated spider vanes, testing the effects of diffraction. Since
then, I had been out with the Wocket (Tele Vue Ranger) and Snuffy
(Starsplitter 10-inch truss dob), but never with Opus. Actually,
that isn't literally true, but the only times Opus had been out was
during the day, when I attached the Wocket plus H-alpha filter to the
Opus's photo bracket for tracking purposes. I hadn't actually looked
through Opus at any time.

Well, that was about to change. I now leave the telescope entirely
set up in the garage (cleared out enough space for that, at least),
and all I have to do is pull it out to the patio, get my chair, take
off the four covers (front and rear of the scope, front and rear of
the finder), slip in an eyepiece (32 mm Plossl to start with), and
I'm off. I didn't bring an atlas or planisphere; as is my usual
tactic now, I just bring my Palm, and do all my star-hopping from
there.

My first target for the night was M27, the Dumbbell Nebula. I didn't
spend much time with it at first, just wanted to make sure I could
still find the darned thing. It's a sign of how late I was up that
this object was already reasonably high up in the sky. I decided I'd
come back for this later, and went on to M57, which I also just took
a quick glance at.

Then to M4, the famous globular near Antares, in Scorpius. I think
it's pretty amazing that I once couldn't see this at all (possibly
under better conditions, but it's hard to compare); not only can
I see it now, but even from home, the well-known north-south bar is
fairly easily visible. What's more, I can tell that the bar is a bit
off north-south--more like a bit north-northeast to south-southwest.

At this point, I decided to put in my reducer/corrector, which I had
left off during last year's Mars apparition. My first target with the
reducer in was Stock 1, a large, sparse open cluster close by Albireo.
Under moderate light pollution (to my eyes, the ZLM was about 4.7),
this cluster is only somewhat detached from the background stars,
with a slight density gradient toward the center, where there are some
10 to 15 stars of magnitude 8 or 9 arranged in a thick V pointed toward
the east. Later, I tried this cluster with the 10x30 binoculars, and
it's definitely more attractive through those.

A bit more interesting is NGC 6823, a medium-rich open cluster about
2.5 degrees to the southeast of Stock 1. It's much smaller, and has
only three or four stars that are easily visible, but I kept getting
the sensation of a secondary layer of stars in the 11th-magnitude range,
or maybe a little dimmer, lingering just beyond. I didn't verify that,
since I would have needed to bring out Snuffy for that, and I didn't
have the energy for that.

I also tried, without much expectation for success, for NGC 6820. This
nebula has long thought to have been identified with a large arc of
gas and dust in which NGC 6823 is embedded, but as Bill Ferris has
noted, the NGC description does not match this object. It seems better
aligned with a small reflection or emission nebula about a quarter
degree to the southwest of the open cluster. This object was definitely
invisible to me without a narrowband filter. With the filter, there
might just possibly have been somethere visible there, but I certainly
couldn't say for sure. I'll have to write it down as a negative
observation.

I tied up the session with a glance at M11. The Wild Duck Cluster was
then in the southeastern sky, which is still well within the light dome
cast by Los Angeles--even at that time of night. But I was able to find
lambda Aquilae, and then through the finder, it's a simple star-hop
around a small crown-like asterism joining lambda to the northern stars
of Scutum, and lying in wait at one corner of the crown is M11. The
cluster takes magnification well in a small telescope, and I could best
see the cluster at around 100x or so, the eighth-magnitude star sitting
just off the corner of the square-edged fan.

After packing up the telescope, I came outside with the binoculars and
looked up (besides Stock 1) Albireo and M27. I forget how enjoyable a
way it is to relax and look up in the sky while sitting comfortably.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

Then to M4, the famous globular near Antares, in Scorpius. I think
it's pretty amazing that I once couldn't see this at all (possibly
under better conditions, but it's hard to compare);

I remember one evening three years ago, with no moon in suburban
Houston, that I couldn't see M4 at all through my 8" Dob. Light
pollution really kills this one. Whereas an inherently much brighter
GC, like M13, shows up much easier in light pollution despite the
greater distance.

A bit more interesting is NGC 6823, a medium-rich open cluster about
2.5 degrees to the southeast of Stock 1. It's much smaller, and has
only three or four stars that are easily visible, but I kept getting
the sensation of a secondary layer of stars in the 11th-magnitude range,
or maybe a little dimmer, lingering just beyond. I didn't verify that,
since I would have needed to bring out Snuffy for that, and I didn't
have the energy for that.

My notes for this one (through a 12" SCT) indicate a core of four or
five bright members, then a gap or sort of "moat", and surrounded by
an encircling ring of many more fainter members. The ring sounds like
your "secondary layer of stars."

I also tried, without much expectation for success, for NGC 6820. This
nebula has long thought to have been identified with a large arc of
gas and dust in which NGC 6823 is embedded, but as Bill Ferris has
noted, the NGC description does not match this object. It seems better
aligned with a small reflection or emission nebula about a quarter
degree to the southwest of the open cluster. This object was definitely
invisible to me without a narrowband filter. With the filter, there
might just possibly have been somethere visible there, but I certainly
couldn't say for sure. I'll have to write it down as a negative
observation.

During the same session we tried for the faint nebula NGC 6820 atop
and around this cluster. My two friends claimed to have seen it, but
I couldn't back them up...

Nice report, thanks.

Ritesh