The year 2016 has been a year of supermoons, almost, with three of these events happening in the last three months of the year – in October, November and December.
The term supermoon was originally used modern astrology for a new or full moon that occurs when the moon is within 90 per cent of its closest approach to Earth in a given orbit, but now they are more often referred to a full moon that is closer to Earth than average. But how close is the question. If well look at Moon’s orbit, it is elliptical, one side (perigee) is about 30,000 miles (50,000 km) closer to Earth than the other (apogee). The term syzygy is the scientific name for when the Earth, sun, and moon line up as the moon orbits Earth. When perigee-syzygy of the Earth-moon-sun system occurs and the moon is on the opposite side of the Earth from the sun, we get a perigee moon or more commonly, a supermoon!
This coincidence happens three times in 2016. On October 16 and December 14, the moon becomes full on the same day as perigee. On November 14, it becomes full within about two hours of perigee—arguably making it an extra-super moon. The full moon of November 14 is not only the closest full moon of 2016 but also the closest full moon to date in the 21st century. The full moon won’t come this close to Earth again until November 25, 2034.
The supermoon of December 14 is remarkable for a different reason: it’s going to wipe out the view of the Geminid meteor shower. Bright moonlight will reduce the visibility of faint meteors five to ten fold, transforming the usually fantastic Geminids into an astronomical footnote. Sky watchers will be lucky to see a dozen Geminids per hour when the shower peaks.
A supermoon, or perigee full moon can be as much as 14 per cent bigger and 30 per cent brighter than an apogee full moon. However it’s not always easy to tell the difference. A 30% difference in brightness can easily be masked by clouds or the competing glare of urban lights. Also, there are no rulers floating in the sky to measure lunar diameters. Hanging high overhead with no reference points to provide a sense of scale, one full moon looks much like any other.
Low-hanging moons, on the other hand, can create what’s called a “moon illusion.” When the moon is near the horizon it can look unnaturally large when viewed through trees, buildings, or other foreground objects. The effect is an optical illusion, but that fact doesn’t take away from the experience.
A supermoon is undeniably beautiful. And we can multiply that beauty by three as 2016 comes to a close. Two supermoons have already gone by and now is the time for the last one of 2016 – December 14 – so mark your calendar and enjoy the super moonlight.