Value-conscious sky watchers can rejoice Monday as the night could bring into focus a rare two-for-one: a supermoon and a seasonal blue moon converged for a single viewing.
NASA says that combination happens roughly every 10 years under the stricter definition of a blue moon — the third in a season with four full moons.
A supermoon happens when a full moon takes place as the moon is its closest to Earth along its orbit. The proximity varies even for supermoon occurrences, with the strongest ones appearing about 14% larger than when a full moon is farthest from Earth. This won’t be one of the stronger supermoons, but it will still be super, NASA said.
The moon’s color will remain off-white and gray, with hints of brown and yellow.
Sometimes the stretch between two appearances of what NASA calls a “super blue moon” can be as long as 20 years, NASA said in a FAQ for Monday’s bright night.
Using a newer definition of a blue moon — the second full moon in a month with two — as well as the more traditional seasonal blue moon definition, would result in a super blue moon every five years or so, the space agency said.
The next time a moon like Monday’s happens — a supermoon coinciding with a seasonal blue moon — will be Aug. 21, 2032, NASA said. The next supermoon that converges with a monthly blue moon will be in January 2037, it said.
Monday’s super blue moon is also a rough indicator of summer’s last 30 days, with the season coming to its end Sept. 21.
“Seasonal blue moons always occur almost exactly one month before an equinox or a solstice,” NASA said in its FAQ.
Many people in the U.S. hoping to take advantage of this rare two-for-one offer could be disappointed: The National Weather Service calls for thunderstorms from the northern mid-Atlantic to New England overnight, with thunderstorms also possible in the High Plains, which includes parts of Montana, North Dakota, Wyoming, South Dakota, Nebraska, Colorado, Kansas, New Mexico, Oklahoma and Texas.
In the San Francisco Bay Area, the viewing looks to be good. The National Weather Service office for the region called for mostly clear skies and “good viewing of the super moon tonight,” according to its latest forecast discussion.
At the San Francisco Giants’ game against the Chicago White Sox, which starts about an hour before sunset, Blue Moon Brewing of Denver plans a postgame drone show for fans at Oracle Park.
The brewer said in a statement, “Following the final out of the Giants game against the White Sox, the ballpark lights will go down and the sky above Oracle Park will light up with a drone show, titled: Once in a Blue Moon.”Â
