"M13 is located in the constellation Hercules, between summertime’s two brightest stars, Vega and Arcturus.
From mid-northern latitudes, the M13 cluster is in the sky for at least part of the night all year round. As you read this, someone, somewhere, is observing M13. In fact, it is above the horizon all night long in May, June and July. In August, September and October, the Hercules Cluster is still very much a night owl, staying up till after midnight.
M13 is very far away, 25,000 light-years. This is several times farther away than the farthest stars you can see with the unaided eye. The light that you see left M13 some 25,000 years ago. And the cluster is large, about 165 light-years across.
Overall, how many stars does M13 have? About 300,000, and perhaps as many as a half million. In fact, that is about 100 times more than the number of stars you can see with your eyes alone in our sky at night.
M13 is a globular star cluster, a huge globe-shaped stellar city teeming with hundreds of thousands of stars. Globular clusters orbit the Milky Way galaxy outside the galactic disk at tens of thousands of light-years away. In contrast, the relatively nearby Pleiades and Hyades are open star clusters that reside within the galactic disk." https://earthsky.org/clusters-nebulae-galaxies/m13-finest-globular-cluster-in-northern-skies/

This project long time pending had its sessions done by Maurizio in April and May 2020 and finally I process in this days. Even not much data was taken, it was with the first gear set we had by that time and of course, with the all tests and mistake we pass trought it.

As it was done with only the L-Pro filter, the workflow was more easy.  The only aditional step I did was beside the normal bilinear stack, the 2 drizzle one, when I finish to process the first stack and saw the result.

The reason was one of the session was done on heavy moonlight condition and that incorporate a lot of fussiness in the definition of the stars cluster so trying to redime that situation, I try the 2 drizzle option in DSS and Siril programs.

Then combine all the stacks processed for obtain the final image, a tedious stack but as the area cropped is almost  half of the area of the total frame, was more easy.  To be honest not much difference I notice between the two types of stacks, but for the sake of finish it and give some sense to the task done (meant try to do the things more dificult than should be -a self critic-),  I finally combine all the fourth results

Just for mention (but not understand the reason of it), it was fun to notice for example that in DSS the clusters stars in bililinear stack were more colorized than the Siril stack, but under 2 drizzle stack, the Siril was more than the DSS and no always the same stars...

The globular clusters are fascinating DSO and I think is a tricky object to catch because of its brightness, you can easily overexpouse its components or underexpose and left behind some inner interesting structures.

Definetely, is a subject that we would like to do again with better data.
We thank you for visit us.

Processed May 2022

https://twitter.com/AstroOtus/status/1528695969151344640