Category: Open Cluster

Discovered by Mechain on the 27th March 1781, M103 became the last entry in Messier’s original catalog. Interstellar extinction of about 1.5 magnitudes makes determining the precise distance difficult but it probably lies about 7200 light years away. The cluster diameter is 17 light years and the bright star in the field is Delta Cassiopeia.

This was the first time that I’d tried out a new piece of software, DSLR_Logger from the AstroTrac Yahoo group. It’s main purpose is for determining precise polar alignment of the mount. I will write more about this program when I’ve had a chance to explore it rather more fully.

This was also the first outing for my new Williams Optics Field Flattener 3 on the 70mm.

Searching through some old folders on my PC I came across 5 images of the Pleiades that I hadn’t previously processed. Taken on the Astrotrac with a 75-300mm Canon zoom lens set at 200mm, each is 3 minutes long for a total of 15 minutes exposure.

The resulting stack had masses of red sky noise but removing this and applying a non-linear stretch starts to show the dust cloud around the brightest stars of the cluster.

This being a Bank holiday weekend, and the skies being cloudy I’ve had some time to review the DVD presentations from the 2009 Mid West Astro Imaging Conference that I bought from Astro Photo Insight some time ago. Two were of particular interest; “The Hows and Why of Image Calibration” by Kevin Nelson of QSI and “Choosing a camera for astrophotography” by Craig Stark. After watching these I decided to evaluate some flats produced by pointing the telescope with Canon 350D at a blank illuminated laptop screen (I used an empty Notepad window). Analysing these images in Maxim, the results were nothing like I expected; less an even grey frame, more a technicolour nightmare!

After that shock I went back to look at my images of the Double cluster and reprocessed them with the new flat frames. Compared to my original efforts there’s much more colour evident in the stars and the overall blueish tint is much reduced. How much of the improvement is down to the flat frames and how much to improved technique is up for debate.  That’s all part of the fun; there’s always something new to learn!

Having bought the book ‘The Caldwell Objects – and how to observe them’ it’s only fitting that I identify this object with it’s Caldwell number rather than the rather nondescript NGC 4755. Located in Crux, The Southern Cross, at a declination of -60 degrees this is a Southern Skies cluster only.

Also known as The Jewel Box this compact cluster is just 10? in size and could be mistaken for a 4th magnitude star with the naked eye. 5,000 light years away , the stars in it are about 15 million years old.

This image is comprised of 28 3 minute LRGB exposures (12,6,6,4).

After I noticed the stars were trailing on the images of M51, I rechecked the polar scope picture when I’d re-positioned for the Double Cluster in Perseus. It required a small tweak in azimuth and I then took 10 3 minute exposures at ISO 400 that were combined in Maxim. The trailing was eliminated and although there was some coma apparent in the corners of the image I removed some of this by cropping the picture. Looks like a field flattener will be required.

In the constellation Vela in Southern Skies is a large open cluster that’s visible to the naked eye. Comprising about 30 stars spread over a 50 arc minute area, it lies at a mean distance of about 580 light years. The individual stars were formed around 36 million years ago.

The individual sub-frames are all of 3 minutes (2x luminance, 1x red, 1x green, 2x blue). To try and get the star colours correct I used a simple utility called eXcalibrator from http://bf-astro.com/index.htm. This uses catalog information from NOMAD to calculate scaling values for the RGB channels. In this case, adjustments were minor (R – 1.0, G – 0.97, B – 1.22). The telescope used was GRAS-10, a TEC-140 refractor.

Since originally posting this image I’ve purchased a copy of Carboni’s Astronomy Tools and added some diffraction spikes to the brightest stars.

While waiting for M82 to rise in the sky I filled in some time taking pictures of M29 in Cygnus. This is a small open cluster set against the backdrop of the Milky Way.

Being very high in the Southern sky this is in an area with very high field rotation so exposure times were very limited on the Alt-Az mounted telescope. I kept to 15 seconds @ ISO 1600 and ended up stacking 20 (car headlights are a particular problem with the telescope pointed in this direction).