Galaxy NGC 3310 (Arp 217)
The galaxy NGC 3310 was discovered by Wilhelm Herschel on 12 April 1789. It is a spiral galaxy of morphological type SA(rs)bc pec. In Halton Arp's 1966 «Atlas of Peculiar Galaxies», NGC 3310 is listed under the number Arp 217 as an example of a galaxy with an attached bow. The escape velocities measured since 2000 range from 952 km/s to 993 km/s and the distances determined from them range from 17 Mpc to 20 Mpc. [145, 196, 199]
On 20 March 2021, a type II supernova was discovered: SN2021gmj. It reached magnitude 15.1. See fig. 1. Previous known supernovae in this galaxy are: SN1991N, SN1974C. [303, 304]
NGC 3310 is a well-studied starburst galaxy thought to have earlier merged with a companion. It shows various tidal formations surrounding the main disc and two large H-I tails extending north and south.  Observations with the Hubble Space Telescope showed a rotating disk of gas at its center, suggesting a supermassive black hole of about 5 to 42 million times the mass of the Sun. 
|Right Ascension||10h 38m 45.6s|
|Declination||+53° 30' 12"|
|Diameter||3.1 × 2.4 arcmin|
|Photographic (blue) magnitude||11.2 mag|
|Visual magnitude||10.8 mag|
|Surface brightness||12.8 mag·arcmin-2|
|Distance derived from z||13.99 Mpc|
|Metric Distance||18.100 Mpc|
|Dreyer Description||cB, pL, R, vg, vsmbMN 15"|
|Identification, Remarks||UGC 5786, MCG 9-18-8, CGCG 267-4, IRAS 10356+5345, VV 356, VV 406, PRC D-15, Arp 217|
NGC 3310 is located in the constellation Ursa Maior, about 10 arc minutes south of the 5.5 mag bright star HR 4156, which on a dark night still is visible to the eye. It is circumpolar and is highest in the sky at night from December to June.
762 mm aperture: Current supernova (SN2021gmj) in galaxy visually clear and well visible.