M13: The Hercules Cluster
I like showing Globular Clusters to visitors to the ‘scope because they are beautiful and their appearance matches the visitors’ expectations (unlike, say, galaxies, which often disappoint an unprepared visitor). M13 is my favourite object, after Saturn and Jupiter, to show people at outreach events. And it’s so easy to find that I’ve taught people how to find it who were then able to go home and pick it out with their binoculars.
Like open clusters, globular clusters are easy to find and observe in small telescopes, pretty, and scientifically important. Globular clusters are made up of 100,000s of very old stars – possibly the oldest stars in the galaxy. (We know this by measuring the content of heavy elements in the stars by analysing the spectra of their light. Heavy elements are made in stars, ejected into space by the death of those stars, and then incorporated into new stars that form. So very old stars have very few heavy elements.) Globulars are located and move in an unusual manner – they are not part of the main disk of the galaxy, and they do not rotate with the spiral arms. Instead, they orbit the core of the galaxy in their own orbits, unrelated to the disk and spiral arms. Explaining how these very old collections of stars came to exist, and explaining their unusual orbits, is a critical test for any proposed model for the formation of galaxies.
Find Vega, the brightest star in Lyra. From Arcturus, sweep your gaze up until you are looking straight up. Continue sweeping in that direction, to a very bright star on the “other side” of straight up. That’s Vega. To confirm, it’s next door to a distinctive diamond of 4 stars.
If necessary, confirm it’s Vega by finding it in the Summer Triangle.
All the above images were generated with Starry Night Pro.