As summer approaches, a different set of constellations make an appearance in the night sky. One of the most recognizable of these is Sagittarius the Archer. Sagittarius is a very interesting constellation as the center of our galaxy, the Milky Way, lies nearby. When you look at Sagittarius, you’re actually looking inward towards the center of our galaxy. That means while you won’t see any galaxies in Sagittarius, you will see a variety of star clusters and nebulae which lie between Earth and the Milky Way’s core.
Sagittarius appears as a “teapot”-shaped pattern of stars in the southern part of the sky. Along the bottom edge of the teapot are several globular star clusters of interest. While globular clusters appear similar through telescopes, they’re very pretty under higher magnifications, and globular clusters contain some of the oldest stars both in our galaxy, and in the universe. In this edition, we’ll take a look at 4 of these interesting star clusters.
First, just to the left of the bottom right corner of the teapot lies M69. M69 lies just under 30,000 light years away from Earth. It’s 42 light years across, and is only 6,200 light years from the center of the Milky Way. M69 is believed to be 13 billion years old, which means the universe was only 700 million years old when it formed. M69 is one of the most metal-rich star clusters on record. It is also relatively dim as far as globular clusters go, although it’s still bright enough to be seen as a fuzzy star in binoculars.
Located midway between the two stars of the base of the teapot is the M70 globular cluster. Appearing nearly identical to M69, M70 lies 29,400 light years away from Earth, and only 1,800 light years from M69. M70 has undergone a core collapse, which means that the stars in the center of the cluster are forced even closer together, making the center of the cluster very bright. M70 is approximately 12.8 billion years old, and is 68 light years across.
To the right of the bottom left star of the teapot lies the special M54 globular cluster. Estimated to be 87,000 light years away and 150 light years across, it is thought that M54 doesn’t belong to the Milky Way! Instead, it is believed to belong to the Sagittarius Dwarf galaxy which is in the process of being consumed by the Milky Way. It is also thought to contain an intermediate mass black hole. Since it lies near the center of the Sagittarius Dwarf galaxy, some astronomers believe that M54 may be the core of the Sagittarius Dwarf galaxy, although it’s not agreed upon. It is thought to be around 13 billion years old. As it is so far away, you won’t be able to resolve individual stars in your telescope even under high magnification. Still, it’s a pretty amazing sight considering that it’s so far away, and may potentially be the center of another galaxy!
Last, we have the M55 cluster which lies to the southeast of the bottom left of the teapot. It may be difficult to spot in northern latitudes as it never rises far above the southern horizon. M55 is large and diffuse, and can be seen with binoculars. It is a metal poor globular cluster, containing mostly older, red stars giving it a rosy- appearance. M55 is figured to be 12.3 billion years old. It is 17,600 light years away, and is around 100 light years across. Finding M55 may be a challenge, but is a great view in a telescope, as individual stars can be resolved fairly easily in a telescope.
Viewing these ancient globular star clusters can be a treat during late spring into the summer months. You’ll be gazing upon some of the oldest stars, and seeing so many stars packed so tightly together is a very gorgeous sight to see. While finding these clusters can be tough without a clear view south for those living in the higher northern latitudes, they are a rewarding find. Next time you gaze at the teapot of Sagittarius, remember the globular clusters along the southern edge and see what beauty they have in store for you!
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