M 28

At about 15,000 or 19,000 light years distance, M28 with its linear diameter of 75 light years appears considerably smaller and more compressed than its more impressive neighbor, M22. It is slightly elliptical shaped according to H. Shapley. To resolve it into stars, larger instruments are required.

M28 contains, in addition its only 18 known RR Lyrae variables, a W Virginis variable (Type II, or population II Cepheid) with a period of 17 days, and a second long period variable (Variable # 17, possibly of RV Tauri type, according to Burnham).

M28 was the second globular clusters where a millisecond pulsar was discovered, in 1987 (the first was