How rare is this week's Friday the 13th Micro Moon?
While it doesn’t officially become full until 12:33 a.m. in the Eastern time zone, Friday night's full moon is a rare one.
Only about 1 percent of full moons occur on Friday the 13th somewhere in the world. This last happened in the Eastern time zone in June 2014, and we won’t see another for 30 more years.
A micro moon, sometimes called a mini moon, is the opposite of a super moon. Super moons look a little larger and brighter in the sky, appearing at perigee, the closest point in the Moon’s orbit to Earth.
Micro moons occurs at apogee, the furthest point in the Moon’s orbit, and look a bit dimmer and smaller. Neither happen on Friday the 13th very often.
The last micro moon on a Friday the 13th occurred in July 1832 and won’t happen again for more than 500 years.
There are 12,368 full moons across 1,000 years of the Gregorian calendar, first adopted on Oct. 15, 1582. Eighty-nine of them fall on Friday the 13th here in the Eastern timezone. Only four micro moons and sic super moons fall on a Friday the 13th. This calendrical coincidences are so rare because because the many ways to measure months do not align very well.
The Moon takes 27.32 days to complete an orbit around the Earth (a sidereal month). By then, the Earth has moved into a new position in its orbit around the Sun. The Moon needs another 2.2 days to get back into alignment with the Sun (a synodic month), bringing on the new full moon.
Neither aligns very well the 7 day cycle of weeks.
With a chance of evening thunderstorms Friday evening, the micro moon will likely be making an appearance between clouds.
Mark your calendar for the next big event in sky, the transit of Mercury on Nov. 11, when Mercury will pass in front of the Sun. If you’ve kept your eclipse glasses from 2017 safe, they’ll help you see the tiny planet as it moves across the disk of the Sun beginning around 7:30 a.m. and continuing over the next 5.5 hours.
