Last Day of Summer, and It's Globular Season Part 1

At least, probably Part 1 (and published later than 9/21....busy, busy, busy!)

Globular Season refers to the vast number of globular clusters visible in the sky. A globular cluster is a large, spherical cluster of stars. They are typically found orbiting the center of a galaxy, and, apparently, formed about the same time as the galaxy. They are typically the oldest stars in (or around) a galaxy.

 Above is a screen shot from the program Stellarium showing the area around the constellation of Sagittarius. The center of our galaxy is very near this constellation. The circles with an + in the middle show globular clusters. Obviously, there are quite a few.

This is the same image, but the box shows encloses the constellation of Sagittarius. There are more than 20 globular clusters within the box. The clusters shown below are all within the box and are all members of the Messier catalog. All images are in black and white. I took the images in color, but there was so little color shown that I think they “show” better in black and white.

M22

M22 was the first globular cluster to be discovered in 1665. The discoverer was Abraham Ihle. It is about 10,000 light years away from us, making it one of the nearer globular clusters. Visually, it's about 17 arc-minutes in diameter. If all the associated stars are included, it's about 32 arc-minutes in diameter, making it larger than the full moon. It it the brightest globular cluster. M22 is notable for two other discoveries: 1) it contains a weak planetary nebula cataloged as IRAS 18333-2357. This was the second planetary nebula discovered in a globular cluster and one of only four known planetary nebula in Milky Way globular clusters. 2) Recent Hubble Space Telescope investigations have discovered “a considerable number” of planet-sized objects that appear to float through the cluster.

M28

M28, which is about 18,000 to 19,000 light years away, is smaller than nearby M22. It was discovered by Charles Messier in1764. M28 is the second globular cluster where a millisecond pulsar has been discovered in 1987. The pulsar spins around its axis once every 11 milliseconds.

M69

M69, as well as M70 below, were both discovered by Charles Messier on the same night, August 31, 1780.

M70