July 30, 2015 Matt Benjamin It鈥檚 called a 鈥淏lue Moon鈥 and Friday evening at dusk if you look to the eastern horizon you鈥檒l get to see one as it rises into the night sky. And what is a blue moon you might ask? It鈥檚 not because it鈥檚 blue. It鈥檚 a term used to describe a second full moon in one calendar month. The first one happened July 2. And it鈥檚 something that doesn鈥檛 happen very often, says Matt Benjamin, education programs manager at CU-麻豆影院鈥檚 Fiske Planetarium.