Hi Mike,
well done - that's an image of
a very large galaxy.
https://fr.wikipedia.org/wiki/IC_2531
How large is it compared to M31 Andromeda?
Some back of the envelope calculations:
There are 2 results for it's distance either 135 mly or 111 mly.
It's angular size = 6.6' from
http://www.wikisky.org/
M31 angular size = 199.5' from
http://www.wikisky.org/
Using both distances in mly.
I scale it with M31 at 2.54 mly.
135/2.54 = 53 times further away.
111/2.54 = 44 times further away.
Using a distance of 135 mly . size = 53 x 6.6' = 350'
Using a distance of 111 mly . size = 44 x 6.6' = 290'
350'/199.5' = 1.75.
290'/ 199.5' = 1.45.
Therefore -
IC2531 is between 45% and 75% larger than the Andromeda galaxy.
M31 is approx 200,000 lys in diameter.
So IC2531 is between 290,000 and 350,000 light years in diameter.
cheers
Allan