Globular cluster M10 in Ophiuchus

The cluster has an apparent size of about 20', which corresponds to a diameter of 83 light-years, given its distance from Earth of 14,300 light-years. Only four variable stars have been discovered in the cluster. M10 is a bright globular cluster in the center of Ophiuchus, observable in the St. Petersburg region in the spring before dawn or in late summer in the evening. In central Russia, it is visible during the short summer nights. It can even be spotted with binoculars. Through a medium-aperture telescope (127–180 mm), M10 resolves into stars, and its core appears offset relative to the halo—similar to the appearance of a comet's head. With larger apertures (from 350 mm), a dual core and a pair of stellar branches radially extending from the core become visible.