Okay, so you know how we have stars in the sky that twinkle and make patterns like the Big Dipper? Well, sometimes groups of stars are closer together and they form what we call a "cluster".
The Eridanus cluster is one of these clusters, and it's made up of about 200 stars that are all hanging out together. These stars are located in the Eridanus constellation, which is a group of stars that are close enough together to form a recognizable shape.
One of the reasons we study the Eridanus cluster is because it gives us a good example of how stars form and evolve over time. It also helps us understand more about the galaxy we live in, the Milky Way, and how it's put together.
It's kind of like a big group of friends hanging out and helping us learn more about space!