OR: Clear sky at last – and a new favorite found…

From: justbeats (steve_beats_at_hotmail.com)
Date: 07/27/04 

Date: 27 Jul 2004 09:34:16 -0700

More ramble than report, but here goes anyway...

On 24/07/04 from 22:30 BST to 03:30 BST I got a session with my 10"
F/10 LX200 (5 weeks since I was last able to use it). The main goal
was to drift align it using a wedge on a tripod to mark out true north
for the pier and observatory I'm installing. This went quicker than I
thought and I had an accurate line set out on the lawn by midnight.

So with hours of unexpected observing ahead and no plan, I started
with a tour of some old favorites. M57, M13, M31 (still low in the
west) and M27 were cool as usual, though M13 was a bit "mushy". The
10" always reveals the extended nebulosity of M27 which sort of hides
the dumbbell shape a little. It always looks like a flattened football
with a dumbbell shaped decal over the middle to me. Tonight was the
same but I couldn't see the central star which was even invisible to
averted vision. This was very unusual because it's always been so
prominent in the past (a fiery electric blue/green point). I put this
down to a new kind of fast turbulence I hadn't experienced before.
Distributed faint nebulosity got through OK, while faint stars were
smeared into invisibility. That's my theory (for now) anyway.

As the night wore on, this high-frequency turbulence calmed and by
3:00am I was able to star test at 420x (this was the last thing I did
before packing up). The collimation was perfect, but I discovered a
tiny tri-lobed flaring close to focus. The flares were about the same
length as the diameter of the in-focus airy disc. Maybe pinched optics
from over-tightening of collimation screws? I was a bit lax in
loosening one for each one tightened when I last did it. It seems
there's some trade-off between collimation holding between sessions
and deformation of the secondary (mine has held collimation for over 9
months now). As the flaring was minor I figured it wouldn't cause a
problem except negligible loss of contrast; so I didn't fix it. I am
concerned that the secondary may be permanently deformed though. Is
that the case, or will it spring back OK when I eventually loosen the
collimation screws?

Light pollution was bad with orange domes on the horizon casting a
sheen over the entire sky – even at zenith (quite rare at my site). So
I decided to try out a Meade Nebular filter again. I was unimpressed
when I first tried it and it sat unused since. I later learnt that the
poor performance could have been because I wasn't dark-adapted, there
was little light pollution anyway and my expectations were way OTT.
This time it made a clear difference, with stars looking much bolder
against a darker sky. It's an excellent (if expensive) LP filter. I
decided to try a real nebulosity and chose NGC281 in Cassiopeia as I
had no idea what it looked like (easy to imagine you're seeing
something with familiar objects). I had a stir around the area without
the filter first. Nice cluster there, but after 15 minutes I'd seen no
nebulosity at all. One minute with the filter though and a faint
mottling emerged. There was NGC281; like cumulus clouds of thin steam
viewed from above with a dark, cloud-free chunk taken out of one side.
It seems this filter does work well after all. Very glad I kept it!

By about 2:00am, I noticed Pegasus low in the south west. I often
avoid this area, especially near the horizon as its on top of a light
dome (Aylesbury). But after success with the nebula filter (and with
it still fitted), I was laughing in the face of light pollution and
decided to have a look anyway (I usually avoid low declinations too –
I'm really living on the wild side this night :-). Being vaguely aware
there are some nice objects in the square of Pegasus, I concentrated
around there, and found the biggest surprise of the night – M15, a
globular I've somehow neglected to see before. Wow!

Maybe it was the slightly iffy seeing, and the light pollution, and
the low declination, but I found this globular absolutely stunning.
M13 is boring in comparison. At 150x an unresolved "aluminum powder"
appearance remained but many stars were visible. I got a clear
impression of a frilly ring of stars or brightness encircling the
core, fading out to a halo with strings of resolved stars at the
periphery. All glittering like Christmas and tinsel. Captivating!

I set my LX200 parameters to search for globulars and had a great hour
GOTOing every other visible globular to compare it to M15. None came
close for visual appeal this time. It will be interesting compare them
in different conditions on another night, but for now I've certainly
got a new favourite in M15!

Interestingly, the "best" images on the web don't show this "frilly
circle", effect. It's completely burned out by the bright core. But
take a look at some shorter exposures (search Google images for M15 or
NGC7078). Some of those do begin to show a frilly ring-like effect
around the core. Just shows that "eyes only" still has a lot to offer
and imaging as deep as possible won't always yield the "best face" of
a (deep-sky) cluster object (IMHO).

And therein lies a potential challenge; have a go at imaging what you
can see rather than seeing what you can image. When my observatory is
completed, I've decided my first project will be to capture an image
of M15 that conveys what I saw through the eyepiece on this occasion;
just to capture the prettiness of it all. Raw depth and resolution
where appropriate...

Great fun!

        Cheers
        Beats

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