From all globulars bright enough to be in reach of amateur's equipment this pair is probably the most prominent in the entire sky. Not only because the chance of having two of them in the very same field of view of a telescope is considerably small (there are only about 150 of them in the entire sky), but also because they are so different in their appearance.

Globular star clusters differ both in brightness and in shape. They are classified according to Shapley und Sawyer in 12 classes that describe how much the star concentration rises towards the center of the cluster. When noticing the difference between the two clusters, you may wonder whether the distance to earth is fairly different between the two and the contrast is just apparent. But interestingly, the distance is comparable, and both size and shape reflect real contrasts within the zoo of globulars that encircle our home galaxy.