M13 – A closer look

After some more analysis at the individual subs for M13 taken on the 12th May 2012 it is apparent that their is trailing in the stars due to poor guiding.  This combined with poor focus (which could be a result of tracking errors) and poor seeing I think has resulted in a lower quality image, lacking colour and sharp detail.  The image itself is still good in my opinion, but I was expecting better.

Take a look at the image here, this is a crop from the top left of a sub, stretched so you can see it.  I know this isn’t my usual spacing issue as the stars are not elongated toward the middle of the image (they would be stretched toward the bottom right in this image) but instead they are rotational.

I knew I had a balancing issue due to adding more kit to the mount and not correctly balancing it, this was shown also in the PHD graph which was far from flat at times.  Unfortunately, due to rushing and trying to make use of the only clear sky in months I wasted it with these mistakes.  I know for next time.  Until then, clear skies!

M13 Great Globular Cluster in Hercules

M13 – Where’s my colour?

12th May 2012 – Finally a break in the persistent clouds we’ve been having in the UK for the last few months, although we have lost Astronomical Darkness where I am located, it’s no excuse to get out and get some imaging done.

Firstly, with Saturn being quite high in the sky I had to train the 100 ED onto it for a bit visual first.  Seeing was poor and I couldn’t really get much detail.  However, I did show my wife and she was very “wow” which is great – her first time seeing Saturn and her rings!

So, after a bit Saturn I re-rigged for imaging and trained the scope onto M13.  M13 is known as the Great Globular Cluster and is located in the constellation Hercules.  M13 is approximately 25,000 light years away from Earth and has an estimated diameter of 145 light years.  To try to understand this a bit more, light travels at 186,000 miles per second, there are 51,556,926 seconds in a year.  So, 186 thousand multiply by 51.5 million is how many miles light travels in 1 year (which should be 5,865,696,000,000 miles per year).  Take this value and then multiply it by 145 (light years).  This gives the distance in miles to M13 from Earth, which calculates to be 850,525,920,000,000 miles.  You could round this off to be 851 trillion miles.

I managed to get around 5 subs off at 120s before the cloud rolled in.  I couldn’t believe it to be honest, but I actually felt good that I had spent a bit time with the night sky.  Anyway, I decided to eat a boil of cereal and drink some tea – as you do.  It was approx midnight when the clouds rolled in and I wasn’t in a hurry to pack up, there was some hope.  Well, my laziness or perseverance paid off, by 00:45 the clouds shifted and it was very clear all the way through to sun rise.  I managed to get to bed by around 04:15 (you might think this is easy but try getting hardly any sleep with a 2yr old!).

Image Details

Subs: 30x120s @ f7.65 (13 rejects from total of 43)
Calibrated and stacked in PixInsight, post processing in PixInsight and CS5.
SW 100 ED DS Pro on HEQ5 guided within QYH5 finder guider.  Imaged with QHY8L OSC cooled to -20

You can see this image plate solved on Astrobin at http://astrob.in/11020/