Mayall II a.k.a. G1 is the greatest globular cluster of the Andromeda Galaxy and the whole Local Group as well. It is the most massive and luminous. It is far bigger than Omega Centauri, the behemoth globular of our own Milky Way. It was discovered by Mayall and Egger in 1953 on a plate made with the 48" Palomar Schmidt (Oschin Schmidt) telescope in 1948. It was the first plate made with the legendary telescope.
The eyepiece impression is rather obscure - it is a 13.8m object with an apparent size of about 15". The core is very bright and stellar. The round symmetrical and diffuse halo gets faint very suddenly outwards. The two close stars are around 14.8m and the third one is about 15.8m according to Guide. There is no sign of resolution.
We took a look at Mayall II in Sándor's 24" Dobsonian at the 2016 MCSE meeting / star party at Tarján, Hungary. The sky was not really good. The globular cluster didn't show any details.
You can see the Hubble Space Telescope (HST) image of Mayall II to the left. I rotataed and cropped my inverted drawing but the photo still depicts a much smaller area (about 30"x30") than my drawing.
Coma Berenices globular clusters
A pair of globular clusters in the spring sky
Perseus planetary nebula
Little Dumbbell Nebula
Face-on grand design spiral galaxy
A unique grand-design barred spiral galaxy in the Virgo Cluster
Coma Berenices galaxy
Grand-design spiral galaxy. One of the biggest members of the Virgo Cluster.
Ultra-thin egde-on spiral galaxy
One of the thinnest galaxies in the sky