The moon will be full on Saturday, and that has some sky watchers proclaiming the arrival of a "blue flower moon." The explanation gets a little convoluted, but the easy part is that May's full moon is often called the "flower moon" because of all the spring blooms, reports CNN. As for the "blue" part: A common (if disputed) definition of a blue moon is that it's the second full moon in a given month—which does not apply here. But the term also is used to describe the third of four full moons in a given season. That one does apply because spring 2019 will have four full moons, is this is No. 3.
“The blue moon is an interesting bit of scientific trivia for those that keep track of these kinds of things,” astronomer Geoff Chester of the US Naval Observatory tells the Washington Post. "There is nothing particularly special about it. Somewhere along the line you’ve got to have an extra moon.” If you want to dig in further to the origins of "blue moon" terms, see this Sky & Telescope explainer. "With two decades of popular usage behind it, the second-full-Moon-in-a-month (mis)interpretation is like a genie that can't be forced back into its bottle," it observes. Whatever you call it, the moon will be full at 5:11pm Eastern Saturday. (Read more full moon stories.)