The phrase “once in a blue moon” has evolved to describe an unusual occurrence. True blue-colored moons are rare, for example, the moon may appear blue when seen through volcanic or fire ash in the atmosphere. In popular astronomy, a Blue Moon is the second of two full moons in a month. January’s first full moon, on New Year’s Day, arrived at full phase at 9:25pm. A second full moon this month will follow 29 1/2 days after the first, reaching full phase on Wednesday the 31st at 8:27am. Not only is it a Blue Moon, it is a Perigean Full Moon that will be eclipsed by the Sun! Perigee, from the Latin “peri-” “around” and “ge” “earth,” conveys that the moon is closest to Earth in its orbit – popularly known as a supermoon.
Joe Rao writes:
“How unusual are Blue Moon eclipses? To answer that question, we consulted the reference book Canon of Lunar Eclipses, 1500 B.C. – A.D. 3000, by Bao-Lin Liu and Alan D. Fiala (Willmann-Bell Inc., 1992). …for a total eclipse of a Blue Moon, we have to go all the way back to March 31, 1866. So, the upcoming eclipse on Jan. 31 will be the first total eclipse of a Blue Moon in nearly 152 years!*
Here in the northeast, the event will be a fleeting partial eclipse that begins at dawn as the big moon approaches the west-northwest horizon. It will be challenging to see even the partial eclipse; it is essential to locate a horizon view. The penumbra (see diagram), which is very subtle, is first visible at 6:20am. Partial eclipse begins at 6:48am. According to Sky and Telescope, “Within 10 minutes, by 6:58am, the lunar orb looks like a giant sugar cookie with a bite taken out of it.” Nine minutes later, 7:07am, the moon sets! The whole timeframe is from 6:20am until 7:07am. Simultaneously, the Sun rises in the east-southeast, also at 7:07am.
In any umbral lunar eclipse, the moon always passes through Earth’s very light penumbral shadow before and after its journey through the dark umbral shadow. Courtesy EarthSky.org
Even if there wasn’t an eclipse, I’d be out there to witness the beauty of the setting full moon at perigee. Add the possibility of catching the shadow of the Earth on the moon’s face and I might climb a mountain in the twilight for a better view.
My impetus for writing about the upcoming lunar eclipse early in the month is to give readers time to make plans, should you be compelled to travel west to see the total or nearly total eclipse somewhere over America. Look closely at the attached map, especially the western two-thirds of the country.
Resources
*https://www.space.com/39241-first-blue-moon-total-eclipse-150-years.html
https://www.space.com/39208-super-blue-blood-moon-guide.html
http://www.skyandtelescope.com/sky-and-telescope-magazine/januarys-total-lunar-eclipse/