This famous objects is known from antiquity, although than it was believed to be simply a moderate brightness star. Today we know that this truly majestic ball of stars (actually, a bit ellipsoidal) is "the grandest" globular cluster in our galaxy. Counting more than million of stars and stretching over 0,5 degree of the sky (actually, a bit more than the Moon disc!), it is easily visible with a naked eye only - unfortunately for those only who have access to tropics or southern hemisphere.
Distance from Earth is roughly 15.800 light years.