It's an opportunity to observe most of the objects in Charles Messier's famous catalog of deep space objects in a single night.

Charles Messier was a French astronomer of the late 1700s. He published an early catalog of deep sky objects. Because he was working with early, primitive equipment, most amateur astronomers today have access to telescopes that equal or better Messier's equipment. This means the objects in the Messier Catalog are easy to observe for modern amateurs. His catalog makes an easy and fun first list of targets to try for.

As the Earth orbits the Sun, all astronomical objects rise and set at different times on different days of the year. In late March and early April, all of the Messier objects are visible in the sky from our latitude at some time during the night. A Messier Marathon is an attempt to observe all of the objects in the Messier Catalog in a single night.

It makes for a fun star party.