Members of the press are calling it a “supermoon.”  The scientific term is “perigee Moon.” These terms mean the same thing: The Moon is going to be as much as 14% bigger and 30% brighter than lesser moons we have seen in the past.

“The last time we had such a close full Moon was January 26, 1948,” says Geoff Chester of the US Naval Observatory, “and it won’t happen again until November 25, 2034.”

Full moons vary in size because the Moon’s orbit is not a circle, it’s an ellipse. One side of the Moon’s orbit (perigee) is 50,000 km closer to Earth than the other side (apogee): diagram. This Monday’s Moon becomes full about 2 hours away from perigee, a coincidence that makes it remarkable.

But will we be able to tell the difference … just by looking?  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.

“I think that the hype over the term ‘supermoon’ is a bit overblown,” says Chester.  “In my book every full Moon has something to offer!”

To get the most out of Monday’s apparition, Chester makes this recommendation: “Try to catch the Moon just as it is rising.”  A perigee Moon magnified by the Moon Illusion could look super, indeed.

Source: Space Weather