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”.

For sale – Acer Aspire One 10.1″ nextbook £50

Hi Folks

I’m selling a nice little netbook if anyone’s interested.

The Spec is as follows:-

10.1″ display . 1024 x 600 resolution

148GB hard drive

1.33GHz Dual Core AMD CPU

2GB RAM (upgradeable to 4GB with Windows 7 64 bit, or Windows 10

Currently has Windows 7 64-bit installed, along with Sharpcap. It will happily run Sharpcap, iSpy, Stellarium etc. Obviourly it won’t handle much post-processing work, or rather it will but you’d have plenty of time to go and make a cup of tea. I was going to fit a SSD but I’ve bought another netbook

3 USB 2.0 ports

1 HDMI port

1 VGA connector

LAN connector

Mains charger

I’m asking £50 for it

I’ll bring it along to RAG on Friday

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!



Informal star weekend at Brow Farm 4th,5th,6th October 2019

Hi Folks,
As I said at the RAG meeting on Friday, I am looking to arrange a Star Weekend at Brow Farm on these dates. When we were at Solarsphere, the Shrophire Astro Group were interested in meeting up with some of our members for the weekend. I think Walsall Astro might also get involved
*** PLEASE NOTE – This is not an official event organised by RAG, so you’d be going as individuals ***
The idea is to just have an informal weekend with hopefully some clear skies and lots of useful advice from friendly chaps. Possibly we can set up some workshops for the less knowledgable (i.e. me ). There used to be some portacabins on site that we can use
For those who don’t know it, Brow Farm is on the edge of  the Long Mynd near Church Stretton, so the skies are pretty dark. These dates are the start of the first lunar quarter They have hard standing, camping fields and numerous camping pods for the non-campers
I’ve spoken to Brow Farm and provisionally booked the flat field so we can all be in the same sort of area.
Can you please reply direct to me if you are interested so I can get an idea of numbers?

Ed Mann

07802 350187

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