Astronomy

Messier 3 is a great globular cluster of the late-spring sky. Image: Adam Block. During late spring or early summer—whichever term you choose, likely depending on how fine the weather has been—is the best time to seek out and observe globular clusters, which are among the most striking and impressive categories of deep-sky objects. Globular clusters are densely-packed, near spherical collections of ancient stars that populate mainly the extended outer halo of our galaxy. They are believed to have formed in the very early life of our Galaxy, over 11 billions years ago; Messier 3 is thought to be 11.4 billion years old. Astounding star densities exist inside even run-of-the-mill globulars; on average, 0.4 stars per cubic parsec (a parsec is equal to 3.26 light years), rising to 100 to 1,000...