The full moon falling later this week on September 16 offers several unique features. It’s the 2016 Harvest Moon, the full moon closest to the autumn equinox. The equinox falls on September 22.
It may also be a supermoon—a full moon that occurs at or close to perigee, the point at which the moons orbit is closest to earth. Not everyone agrees whether September 16’s moon will be a supermoon. An astrologer (not an astronomer), Richard Nolle, is credited with coining the term supermoon, and he does not include September 16 as one of the supermoons occurring in 2016. His list of supermoons includes full moons that fall at their closest perigee for the year.
However, Nolle’s original definition of a supermoon was “a new or full moon which occurs with the Moon at or near (within 90% of) its closest approach to Earth in a given orbit.” Astronomer Fred Espenak therefore calculates the supermoon based on the perigee of each orbit, and includes September 16 as a supermoon. (Bruce McClure, earthsky.com/tonight) Either way, it’s bound to be big and beautiful, if clouds don’t get in the way.
In addition to being a harvest moon and possibly a supermoon, September 16 will also offer a subtle penumbral eclipse in earth’s eastern hemisphere—unfortunately not visible in the U.S.
For more details about this week’s moon show, follow the link: http://earthsky.org/astronomy-essentials/harvest-moon-2
