Galactic clusters like Pleiades and Hyadam and globular clusters are similar in the following respects:
a) They consist of stars of different spectral classes.
b) They are gravitational systems, as obvious and certain as binary stars, although the periods of revolution or oscillation of stars relative to the gravitational centers of clusters are immeasurably long.
c) Their distribution across the sky indicates their belonging to the galactic system.
d) In almost every galaxy cluster, the brighter stars are indeed brighter: they are giants compared to the Sun, and often supergiants.
Differences are more significant than similarities:
a) Galaxy clusters are closely related to the Milky Way:
all of them, with the exception of two or three, are from the galactic plane at distances not exceeding three thousand light-years; globular clusters known to us are found in all galactic latitudes, they are more numerous near the borders of the Milky Way, but there is not a single cluster located
closer than two thousand years from the galactic plane.
