Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the Messier 18 open star cluster. Enjoy! In the 18th century, while searching the night sky for comets, French astronomer Charles Messier began noticing a series of “nebulous objects” in the night sky. Hoping to ensure … Continue reading Messier 18 (M18) – The NGC 6613 Star Cluster