If the full moon looks like it's a little larger than usual this weekend, that's because it is -- or at least, because it's a little closer than usual.
Saturday night marks the year's "super moon" -- the name given to the full moon that best coincides with the moon's closest pass to Earth in any given year. (The full moon is technically at 4:30 a.m. Sunday but the moon will look most dramatic just after sunset Saturday evening when it's low on the horizon.)
The moon's orbit around the Earth is slightly elliptical which means there is about a 27,000 mile variance between the moon's closest point (called "perigee" ) and furthest point (called "apogee") each month. The "super moon" is the name given each year to the full moon that happens closest to the perigee.
This year's super moon will have the moon at exact "full" status sitting at 221,334 miles away from Earth -- just 22 minutes after the moon reaches its closest point -- according to EarthSky. It isn't quite as "super" as last year's super moon when it was 23 miles closer.
However, the moons get "extra" super in the coming years, EarthSky reports: 2014's super moon (Aug. 10) will be 59 miles closer than this year ("Super Duper Moon?") and in 2015 (Sept. 28), it'll be even another 13 1/2 miles closer (perhaps coinciding with the Sonics' return? A "SuuuuuuuuuuperSonics Suuuuuuper moon?") and in 2016 (Nov. 14)? The closest Super Moon of the decade when it's almost 300 miles closer than this year. (A "Supercalifragilistic..." well, you get the idea.)
In each instance, the moon will appear about 14 percent larger than when it's at apogee, but it'll be hard to notice with the naked eye.
What you might notice instead is that the moon could look artificially super large when it is on the horizon as it's setting and rising just before and after sunset. That's due to the mysterious moon illusion where full moons near the horizon apparently trick the human eye into making it look larger than it is -- an effect that will be enhanced this weekend. Scientists have yet to explain how the illusion works, but suffice to say "object on horizon may appear closer than it really is."
The supermoon will bring unusually high tides because of its closeness and its alignment with the sun and Earth, but the effect will be modest, says Geoff Chester of the U.S. Naval Observatory.
The forecast is looking like it'll cooperate for Seattle with mostly clear skies expected at sunset Saturday evening -- the best time for the show will be just after sunset when the moon rises around 9:30 p.m.
If you're up early Sunday, you can get a similar effect as the moon sets just before sunrise (5:10 a.m.) in the west. Sky forecasts are reasonably clear for the Puget Sound area early Sunday but socked in on the coast so there, I'd go with Saturday evening's show.
If you get any great photos, we'd love to see them. Local photographer Liem Bahneman gave some great photography tips after last year's moon.
You can post them to our YouNews site or email them to our station!