Astronomy Picture of the Day . The Hydra Cluster of Galaxies . ... A Violet Moon . ... The view looks down on the Moon.. Tonight: A Blue Moon . ... In fact, the modern usage of the term "Blue Moon" refers to the second Full Moon in a single month. ... Huck Finn's New Sky View . ... Astronomer Bill Keel took the picture earlier this month (July 7) while standing near the summit of Hawaii's Mauna Kea contemplating the sky in the direction of the center of the Galaxy (right of picture center). ...