The full moon is looking bigger and brighter this week than it’s looked since 1948 – and although you may not notice just how much more super this “supermoon” is, it’s definitely worth looking up. If the skies are ever clear, that is.
The moon is due to be at its closest at 3:22 a.m. PT Monday, and it’ll reach the peak of its full phase a few hours later at 5:52 a.m. The bottom line is that the lunar disk will look about 14 percent wider than it does at its farthest distance from Earth, and shine about 30 percent brighter.
This doesn’t mean you’d have to get up in the wee hours of Monday morning to catch a super view.
“I’ve been telling people to go out at night on either Sunday or Monday night to see the supermoon,” Noah Petro, deputy project scientist for NASA’s Lunar Reconnaissance Orbiter mission, said in a NASA feature about the phenomenon. “The difference in distance from one night to the next will be very subtle, so if it’s cloudy on Sunday, go out on Monday.”
Seeing the moon on the rise just after sunset, in autumnal twilight, can make for a romantic picture. And some say the moon looks biggest under those conditions, due to what’s known as the “moon illusion.” But German science writer Daniel Fischer argues in his Sky & Telescope preview that the sight is actually most super at midnight, when the moon’s glow is directly above. This chart illustrates the difference.
“As the moon arcs from the horizon to nearly overhead, its distance changes by a few thousand kilometers,” he explains. “This changes the disk’s apparent diameter by about 1 percent.”
So-called supermoons result from the combination of factors. Because the moon traces an elliptical rather than a precisely circular orbit around Earth, its distance shrinks and grows over the course of each lunar cycle. If the moon happens to be relatively far away at the time that it’s full, it looks smaller and shines less brightly than average. If it’s super-close, it’s bigger and brighter than average.
Some skywatchers take the view that a supermoon occurs anytime the moon goes full when it’s within 90 percent of its closest approach to Earth. By that measure, this is just one of several supermoons taking place during the latter half of the year.
I prefer to define a supermoon more simply: It’s the closest full moon for a given year. By that measure, this month’s full moon is the one and only supermoon of 2016. That turns Monday into a “Moon-day” worth celebrating as a loony holiday.
Seattle’s November weather isn’t ideal for catching this week’s supermoon. The forecast calls for cloudy skies until midweek. But even then, it’s worth taking a moment with an almost-super moon. And if we’re completely clouded out, make a note to look for photos on SpaceWeather.com.
While you’re at it, mark your calendar for the supermoons ahead. But you’ll have to mark a lot of calendars to get to an opportunity as good as this week’s: The next time the full moon comes this close will be in the year 2034.