Messier 22: A Stunning Globular Cluster in Sagittarius

Messier 22, also known as M22 or NGC 6656, is a remarkable globular cluster situated in the constellation Sagittarius. Globular clusters are densely packed groups of stars that orbit the Milky Way’s halo, and M22 is one of the most magnificent examples. Containing over 100,000 stars, this cluster lies approximately 10,800 light-years away from Earth, and its 32-arcminute glow, about the size of the full Moon, spans roughly 100 light-years. Its compact nature and high concentration of stars give M22 a stunning appearance when viewed through telescopes.

M22 is particularly notable because it is one of the closest globular clusters to Earth, making it one of the brighter globular clusters in the sky. In fact, only two globular clusters in the whole sky, Omega Centauri and 47 Tucanae, outshine it, and both are deep southern objects. With its densely packed stars, a planetary nebula, and two candidate black holes, M22 offers much to astronomers and stargazers alike.

Magnitude

Messier 22 has an apparent magnitude of +5.1, which means it is bright enough to be seen with the naked eye under very dark skies, though binoculars or a telescope are usually recommended for clearer viewing. Its brightness and proximity make it a popular target for amateur astronomers, particularly during the summer months when it is most prominent in the night sky.

Season and Prominence

M22 is best observed during the summer months, particularly from late June to August. During this time, it is high in the sky during the evening hours, providing an excellent opportunity for stargazers to observe it. Its location near the center of the Milky Way galaxy means that it is often seen against a rich background of stars, enhancing its visual appeal.

In late June, observers in the Northern Hemisphere will find M22 rising in the southeast after sunset and reaching its highest point around midnight; by mid-August it is highest around 9 p.m. From about 40°N it climbs only about 26 degrees above the horizon. It is also visible in the Southern Hemisphere, where it appears much higher, nearly overhead.

Constellation

Messier 22 is located in the constellation Sagittarius, also known as "The Archer." Sagittarius is a prominent summer constellation and is easily recognizable due to its characteristic “teapot” asterism. M22 is situated just above the lid of the teapot, making it relatively easy to locate once you've found the constellation.

How to Find M22

To locate Messier 22, start by finding the Sagittarius constellation. The teapot asterism within Sagittarius is an excellent guide. Find Lambda Sagittarii (Kaus Borealis), the star at the top of the teapot's lid. M22 lies about 2.5 degrees northeast of it, roughly along the line from Gamma Sagittarii at the tip of the spout through Lambda. The smaller globular M28 sits just 1 degree northwest of Lambda, so the two make a good pair.

For binocular observers, M22 will appear as a faint, fuzzy patch of light. A small telescope will resolve the cluster into a dense, grainy ball of stars, while larger telescopes will reveal individual stars in the cluster's outer regions. Under high magnification, the core of M22 can appear like a swarm of bees, with countless stars tightly packed together.

History

Messier 22 was discovered by the German astronomer Abraham Ihle in 1665, making it one of the earliest known globular clusters. Charles Messier added it to his famous catalog of celestial objects on June 5, 1764. Messier described it as a round nebula in which he could see no stars; later observers with larger telescopes resolved it into a dense ball of stars.

Throughout the 20th century, M22 continued to intrigue astronomers. In 1986, data from the IRAS infrared satellite revealed a planetary nebula within the cluster, making it one of only a few globular clusters known to contain such an object. In 2012, radio astronomers using the Very Large Array reported two stellar-mass black hole candidates in M22, a surprise because theory had suggested such black holes would be thrown out of a cluster.

Conclusion

Messier 22 is a captivating object in the night sky, offering amateur and professional astronomers alike the chance to observe one of the brightest and closest globular clusters to Earth. Nestled in the rich constellation of Sagittarius, this ancient cluster provides a glimpse into the early history of our galaxy. Whether you’re gazing at it with binoculars or resolving its individual stars with a telescope, M22 is a must-see target for any stargazer during the summer season.