[AJames]

Glen

Yes, Dunlop did describe the stars as a globe, but the term only meant as a cluster of stars not a globular star cluster per se. I.e. All the star clusters were viewed as the same. I think you will find that the word "globular cluster" is a far more modern invention.

According to some, the true "globular" classification was by John Herschel in "Catalogue of Nebulae and Clusters of Stars" the Royal Phil.Trans., 154, 1 (1864). However, others say it was the 3rd Earl William Parsons Rosse around 1845, who began to resolve the cores, and revealed the tens of thousands more stars than any open cluster. Needles to say, the first written term was John Herschel.

The main reason was NOT that globulars looked different from the open clusters, but because they were relatively so rare objects. After Dunlop, 49 were known, and most of them remained either unresolved or poorly examined. This had only increased to 56 in 1840, and even the NGC in 1888 listed only 66.

The "real killer" for globulars came with the first observations of variable stars, which showed that the distances of these objects were away from us - anagalactic distances and not within the nearby arms of the Galaxy like the open clusters.

"Globular Day", if one was ever to be recognised, is the 18th May 1860. This was when Arthur Auwers discovered the nova in globular M80. Peaking at 6.7 magnitude, it remained at this magnitude for three days, only to eventually fading beyond telescope view on the 16 June 1860 around 11th or 12th magnitude. Its intrinsic brightness, if it was indeed associated with the cluster, suggested these objects were perhaps fundamentally quite differ-
ent from the open clusters. Until 2007, the only other galactic globular nova that we have observed was within NGC 6553 (V1148 Sgr) in 1945.

The first of the regular globular variables were casually discovered in 1881, and the first of the important RR Lyrae pulsating variables was by Solon Bailey in 1895. In our far southern skies, the first variables were found in Omega Centauri by Pickering in 1893 and 47 Tucanae by Bailey in 1902.

It was Harlow Shapley between 1916 and 1918 who cemented globulars as separated types, finding the old RR Lyrae variable stars and using them to establish they were many kiloparsec distances. Walter Baade eventually used globulars in 1944, and determined the fundamental distinction between the Population I and II stars within the Milky Way Galaxy. This became the key. The ages of globulars were much older than the typical brighter stars seen in the Galaxy.

This finally killed and severed the old links between globulars and open clusters.

Andrew