Universe Today
Description:
History of Observation:
"In the night of May 28 to 29, 1764, I have determined the position of a new nebula which is situated in the right leg of Ophiuchus, between the stars Eta and Rho of that constellation; that nebula doesn't contain any star; I have examined it with a Gregorian telescope which magnifies 104 times; it is round its light is faint, and its diameter is about 3 minutes of arc: its right ascension is 256d 20' 36", and its declination 18d 13' 26" south."
"May 3, 1783. I viewed the nebula between Eta and Rho Ophiuchi, discovered by Mr. Messier, in 1764. With a 10-feet reflector, and a magnifying power of 250, I see several stars in it, and make no doubt a higher power, and more light, will resolve it all into stars. This seems to be a good nebula for the purpose of establishing the connection between nebulae and clusters of stars in general. On June 18, 1784, the same nebula viewed with a large Newtonian 20-feet reflector showed a very large and very bright cluster of excessively compressed stars. The stars are but just visible, and are of unequal magnitudes: the large stars are red; and the cluster is a miniature of that near Flamsteed's 42d Comae Berenices."
"A globular galaxy-cluster, on the Serpent-bearer's left leg, with a coarse telescopic double star in the np quadrant. This fine object is composed of a myriad of minute stars, clustering into a blaze in the center, and wonderfully aggregated, with numerous outliers seen by glimpses. It was registered by Messier in 1764; and described by him as a nebula, "unaccompanied by any star." The mean apparent place was carefully differentiated from Eta Ophiuchi. Sir William Herschel resolved it with his 20-foot reflector, in 1784; and he estimated its profundity as, at least, of the 344th order. He thinks it a miniature of No. 53 Messier; and it is one of those which forms a capital object, for proving space-penetrating power of a telescope. It lies 3 deg to the south-east of Eta, and rather more than a quarter of the way from Antares to Altair."