Lunar data mining and “Alexander’s beaded rim”

October’s “Sky at Night” magazine has quite a few lunar images. The regular “Moonwatch” article is about the crater “Alexander” and its environs. Alexander is a difficult to identify eroded crater. In particular it talks about “Alexander’s beaded rim” about which it says “The peaks that define Alexander’s western rim appear like tiny stars arranged in a beautiful arc”. I have to confess that from the images in the magazine, this clair-obscur effect totally eluded me.

So, as I now have quite an extensive set of window-sill based images (of varying quality!) of the Moon in a variety of phases a bit of data mining was indicated. I found the following image which I cropped and labelled the features to be approximately the same as that in the magazine;

Then, after a bit of contrast stretching in GIMP, we get this:

NOW I can see an effect, although whether it is the one they were talking about, I don’t know! It is pretty though.

While looking at this image set, nearby there was also a pretty good manifestation of the Lunar “V”.

Another attempt at Mons Rumker 11/09/2019

I have been trying for a long time to get a reasonable image of Mons Rumker to add to my lunar dome images. See

Rumker, being so close to the limb, is very tricky to get the terminator lighting and libration state right. Here is another go tonight. Slightly better than the last effort above, I fancy, but still not wonderful.



Another DSO challenge – the Hickson catalogue

The appearance of Pegasus reminds me that there are a couple of well-known compact galaxy clusters in that constellation. One of them, Stephan’s Quintet is included in a catalogue of galaxy clusters – the Hickson catalogue

It is a pretty challenging set of targets for all you astrophotographers out there! There is a sub-set of the easier ones (!) at

I have only managed to image 3 out of this list, so far, and here are some PD images from my archive to wet your appetite.

Hickson 44, comprising NGC3187, NGC3193, NGC3190 and NGC3185

Hickson 68, comprising NGC5350, NGC5354, NGC5353, NGC5355 and NGC5358

Hickson 92 (including Stephans Quintet), comprising NGC7320C, NGC7320, NGC7319, NGC7318B, NGC7318A and NGC7317

The other well-known cluster in Pegasus is the Deer-Lick group, comprising NGC7336, NGC7335, NGC7331, NGC7340 and NGC7337

Happy imaging!



GIMP, Reprocessing and C12 / NGC6946

Many thanks to Andy for posting his instructions for image processing – obviously caught the bug!

Its nice that someone else is also trying things out. The simple method there for reducing star trails had never occurred to me for example!

There are many different ways of achieving an objective once you have a general purpose toolbox, and often a combination of methods is the best option, The GIMP “pyastro” plugin is pretty good for rounding stars for instance, but doesn’t always work, especially when the stars are in front of an extended DSO.

That brings me to C12 / NGC6946. Rob has just posted a really good image of this. I posted one way back in 2015 (that is very poor compared to Rob’s) at

It suffers from all sorts of problems such as star trails and halos, so can we do anything about it?

I’ll not bore everyone by recounting the exact sequence of processing steps, as it will be different for every image.

Suffice it to say it was a combination of despeckle / star trail reduction / and dehaloing as I described here:

The dehalo method for deep sky objects using GIMP.

Anyway, here is the original as posted, and the reprocessed version.

Still not a patch on Rob’s, of course!

Instructions for processing images in Nebulosity and GIMP

The sets of instructions I have written based on advice I have been given or read so far….subject to later revision. Due to my limited knowledge of astrophotography, there may be errors in these documents.


How to remove light pollution from astronomy photograph in GIMP 250819

How to stack frames in Nebulosity 4 (without darks) Damian 310819

How to process dark frames in Nebulosity Damian 080919

Instructions on how to take dark frames from Damian 030919

Sorting out elongated star images (star trailing) in astrophotos 270819

Damian re-processes Andrew’s M101 image from 24/8/2019 in Nebulosity and Photoshop

Better outcome that my previous attempts. Also multiple small galaxies indentified by comparison with a better widefield image (not mine) – overlaid below – my apologies that stars don’t quite match



Damian’s version my M101 from 240819 on 080919 overlaid with better widefield M101 picture, showing multiple small galaxies, many of which are evident also in image above (due to poor alignment many stars appear twice close to each other):

Weekend Opportunism

Between a busy work week, family commitments and some so-so forecasts it wasn’t looking good for astronomy this weekend, but it turned out pretty well.

Friday Night:
Didn’t get out until about 10:30 but tried to make up for lost time by setting both the main scope going and trying out my 50mm lens on the Star Adventurer. I had high hopes for the 50mm lens- it’s another oldie (I’ve had it about 15 years), but online quite a few people are getting great results with them. Well- I’m not in that club (yet). The diaphragm only has five blades and although I stopped it down to f2.8 (it’ll open up to f1.8) all of my stars are pentagons and DSS is refusing to recognise them as stars- so no results from that. Fortunately, the main rig saved the day: I went for NGC6946 – The Fireworks Galaxy with my 200p. Throughout the session low clouds were interrupting the view, and around half the subs were lost, but the ones I did hang onto gave the result below. Over the summer I’ve picked up a second hand Canon 550d that has been home modified with a Peltier cooler and put into a metal case- it’s not pretty, but it seems to be effective. This is 13×4 minute subs and throughout this session it held the temperature down to around 7-8 degrees which I’m pleased with (a couple of degrees below ambient, my 600d usually runs about 10 degrees above ambient and is consequently much noisier). The target itself is quite a bit smaller than I’d anticipated- this is a crop of about 20% of the frame. Despite the small size- I think this is a lovely target- both for its colours and the asymmetry in the arms.


Whilst the cameras were doing their stuff I had the Dob out on the following objects:

The Double-Double- I used Vega to get the finders lined up then dropped down to Epsilon Lyra to check out the seeing. It was a straightforward split, but I could see that the transparency was not great.

M13 & M92 – I often start with these and never get tired of them. In Binoviewers at about 260x they fill the field of view and appear 3 dimensional. For me these are the only types of objects that actually look better in the eyepiece than in a photo; I love the difference in their appearance- M13’s great with lots of features, but a bit of a mess with arms everywhere, whereas M92 is compact and very neat. Just wonderful.

The Veil – I was reading a thread on SGL recently which referenced a Sky and Telescope article on The Veil ( . Using this as a guide, and with an Oiii filter a 30mm eyepiece (55x) and a coat over my head I managed to explore just about the whole thing. I’m a bit prone to hopping from object to object whilst observing, so it was great to really take my time in the tranquillity of the small hours and drink it all in with nothing but the odd clunk of a shutter release and that American woman with the nice voice who commentates on APT saying “Dithering started…” softly in the background. Ahhh… a very nice dither contemplating the remnants of a supernova.

I was on the Veil for over half an hour and loved every minute of it, but decided with to move on with the Oiii filter and go check out M27. This is normally not a problem, but by this point the transparency had deteriorated so much I was unable to hop to it. Altair was the only nearby star that was naked eye visible and despite several attempts I just couldn’t find the stars in the finder to hop up to M27. Reluctant to retire I switched up to the North East to check out M31 as the skies looked better in that direction. Before I could get to it a bank of cloud blotted it out. Time for bed…


I managed to pop out briefly whilst doing other things on Saturday evening and set the imaging rig running on M13. This was a bit of an experiment: I’ve imaged M13 before, but with my guide camera on a smaller scope using the short exposure method. Whilst I was quite pleased with those outcomes (see , I wanted to see how it would look with more integration time and a DSLR chip. This is 22x 4 min subs plus calibration frames and I am really pleased with it. As a bonus for the last half-hour it was running I sat outside with Sam observing the sky primarily with Mark 1 eyeballs. After a while we were both able to pick out the Milky Way running up through Cassiopeia and Cygnus despite the local light pollution. A real pleasure!