Details in M31 (NGC206 star cloud, G76)

[acey]

23.9.09

Transparency 5.8

12" Flextube

I decided to take a look at some details in M31. Luginbuhl and Skiff have an annotated photo in their observing guide and this was what I used.

I first found the star cloud NGC206. This has its own NGC designation because Herschel included it in his catalogue: he didn't

include Messier objects but did include what looked like separate pieces. In photos the star-cloud is obviously part of the galaxy, for example here:

NGC206 Open Cluster with Nebulosity in The Great Andromeda Galaxy

But through a telescope you need to move away from the bright solid mass of light at the core and into the whispier regions of the arms. M32 and a comparably bright star beside it are the stepping stones to NGC206.

In the 12" at x50 the cloud was a little hard to pick out from other knots and star groups in the vicinty, but at higher power it stood out clearly as an elongated patch of moderate, uniform surface brightness. At x150 I could clearly see it, a narrowing strip whose tip fades into the continuation of the spiral arm it lies on. A couple of other bright knots, much smaller, were visible in the vicinity.

I could see why Herschel gave it its own number. Through the scope, you could imagine it as being a separate object, right on the edge of M31 whose spiral arms form a blotchy and discontinuous background.

I found that a UHC filter enhanced the view - in fact it helped me to see the general structure of M31 in better detail, presumably because the cloud and numerous smaller ones like it contain nebulous material.

It's also possible to track down globular clusters in M31. I've never tried because they all look stellar and I like my DSOs fuzzy, but since I was in the neighbourhood and I had Luginbuhl and Skiff open in front of me, I had a go at G76, one of the brightest globs in M31, which lies very close to NGC206.

Using the photo it was very easy to find. I fancied that with averted vision I could see it as non-stellar but that was pure fantasy and wishful thinking on my part. Even in CCD images it looks like a star, e.g. here:

M31 Globs

Still, this little speck was by far the most distant glob I'd ever seen - the only extra-galactic one. I plan to have a go at other details in future, using this:

Atlas of the Andromeda Galaxy

For now, though, clouds brought an early end to my session. Only other thing I'd managed was a re-observation of Abell 2666 in Pegasus which had defeated me last time round. This time I easily found its brightest galaxy NGC7768, which had an interesting appearance with an apparent double core, due to the presence of a foreground star just west of the actual core. But even using a photograph, I could barely glimpse any of the other galaxies in the cluster.

Andrew

[acey]

Deatils? I obviously didn't get enough sleep.

Make that "details".

[ashenlight]

Andrew, what a superb write up of a very interesting observing session. It must be really mind blowing to see such detail on an object outside our own galaxy and 2.5million ly away. Congratulations on spotting them, what a wonderful achievement I would never have thought you could make out such detail from ground based telescopes.

Thanks for sharing with us, great work it's such a shame there isn't another galaxy so close to us!

[Beyond_Vision]

A great write up Andrew it sounds like you had a fantastic night

Regards

Kevin

[oceanheadted]

Wow, I hadn't even imagined you could see that kind of stuff all that way away from a ground based telescope. Good post!

[dobserver]

Very interesting reading, thanks for sharing.

Steph

[Doc]

This is pretty in depth stuff Andrew and I think you done fantastic to make out some Globular clusters in M31. According to those links there are 75 of these Globs in the Andromeda galaxy.

Great report and It's something I must try myself under darker skies.

[acey]

G76 has a reported visual magnitude of 14.2 - and is starlike - so it's interesting to ask what sort of minimum aperture and transparency are needed.

From my site the object was 8.4 magnitudes fainter than my naked eye limiting magnitude. If I assume my pupil was 6mm so that the aperture factor (mirror diameter / pupil diameter) was 50, then the magnitude gain of my scope, 5log(aperture factor), was 8.5, meaning I should stars down to 14.3 through the telescope. So I was theoretically within 0.1 mag of the faintest thing I could hope to see.

In fact I could have gone quite a bit fainter - G76 was easy with direct vision. So if my sky had been a bit lighter I reckon I would still have seen it with the 12". I think it's worth a shot from moderately light-polluted skies with that sort of aperture. From a dark site, I'm sure a 10-inch would manage, and maybe less.