Discovery: Along with all the other "Palomar xx" globulars, Palomar 13 was discovered by George Abell.
Physical Information: Palomar 13 is currently about 75 to 80 thousand light-years from the Sun, in the halo of our galaxy. It is one of the faintest halo globulars, making it a difficult object to study, and although it has been the subject of a few studies since the late 1990's, results have been varied. It has a very low metallicity (presence of atoms other than hydrogen and helium) of only about 1% that of the Sun, a fairly typical result for halo globular clusters. Estimates of its age range from 11 billion years (fairly young for such an object) to nearly 14 billion years (more than the current estimate age of the Universe, so obviously wrong), with the most likely value being about 12 billion years. Studies of its mass to light ratio and internal motions suggest that it has either undergone a relatively recent disruption, or has an unusually extended halo of unknown nature, which is more typical of dwarf spheroidal galaxies than globular clusters. The (very eccentric) orbit of Palomar 13 changes its size and orientation from one orbit to the next, but its distance from the center of our galaxy appears to always be at least 10 thousand light-years at perigalaxion, and can exceed 60 or 70 thousand light-years at apogalaxion; however, gravitational interaction with the central bulge of our galaxy at its most recent perigalaxion, about 70 million years ago, may be responsible for the possible "disruption" noted in the previous sentence, and it has been suggested that its next near approach to the center of the galaxy (about a billion years from now) may completely disrupt it.) Estimates of its apparent size range from 0.7 to 1.8 arcmin, the wide range presumably being due to its low central concentration making it hard to tell where it ends. Based on the images below, I have estimated an apparent size of about 1.8 by 1.7 arcmin. Given that and its distance from the Sun, it is about 40 light-years in diameter.