who were among the observers of this collection of stars?
Abraham Ihle and William Herschel.
Globular cluster
The first known globular cluster, now called M 22, was discovered in 1665 by Abraham Ihle, a German amateur astronomer. However, given the small aperture of early telescopes, individual stars within a globular cluster were not resolved until Charles Messier observed M 4 in 1764. The first eight globular clusters discovered are shown in the table. Subsequently, Abbé Lacaille would list NGC 104, NGC 4833, M 55, M 69, and NGC 6397 in his 1751–1752 catalogue.

When William Herschel began his comprehensive survey of the sky using large telescopes in 1782 there were 34 known globular clusters. 
how many globular clusters are in the milky way About 150 to 158 currently known what are these? It is a spherical collection of stars that orbits a galactic core. do they contain metal? It consists of Population II stars, to which astronomers refer to as heavier elements as metals and to the proportions of these elements as the metallicity. how the last term calculated? Astronomers use several different methods to describe and approximate metal abundances, depending on the available tools and the object of interest.
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Globular cluster [SEP] Observation history
The first known globular cluster, now called M 22, was discovered in 1665 by Abraham Ihle, a German amateur astronomer. However, given the small aperture of early telescopes, individual stars within a globular cluster were not resolved until Charles Messier observed M 4 in 1764. The first eight globular clusters discovered are shown in the table. Subsequently, Abbé Lacaille would list NGC 104, NGC 4833, M 55, M 69, and NGC 6397 in his 1751–1752 catalogue. When William Herschel began his comprehensive survey of the sky using large telescopes in 1782 there were 34 known globular clusters. Herschel discovered another 36 himself and was the first to resolve virtually all of them into stars.