If the full moon looks a bit bigger and brighter in Saturday night's sky, you're not seeing things: It's just the "supermoon" — the biggest moon of 2012. And there's a meteor shower from Halley's Comet that's peaking as well, adding to the sky show.
The full moon of May will hit its peak overnight Saturday night and early Sunday, just one minute after the moon makes its closest approach to Earth. The timing means the moon, weather permitting, could appear up to 14 percent bigger and 30 percent brighter than a full moon at its farthest distance — an event scientists have nicknamed the "supermoon."
The moon will be at its fullest at 11:35 p.m. ET just after hitting perigee, the point in its orbit that brings the moon closest to Earth. The technical name for the event is a "perigee moon."
The moon will be about 221,802 miles (356,955 kilometers) from Earth, about 12.2 percent closer to our planet than when the moon is at apogee, its farthest point. The average Earth-moon distance is about 230,000 miles (384,400 kilometers).
The last time a supermoon occurred was in March 2011. That supermoon was actually closer to Earth than the moon will be tonight by about 248 miles (400 kilometers). [Amazing Supermoon Photos from 2011]
Big moon rising
A good time to watch is during moonrise or moonset. At these times, the moon can appear much larger than when it is higher in the sky. The view is actually an optical illusion.
The moon is no larger than it is when it's overhead in the night sky and you can prove it yourself. Here's how: When the moon is low on the horizon, measure its size with a ruler or your thumb and forefinger. When it's higher up in the sky, try again. The distances will be the same.
The precise time of moonrise varies, depending on location. For observers in California, the moon will rise at about 7:37 p.m. PT. Skywatchers with a clear horizon on the East Coast will see it rise at 7:46 p.m. ET. You can find the exact time for your location using the Old Farmer's Almanac.
The extra big full moon of May can mean higher tides on Earth, an effect called "perigean tides," but there is no chance of the supermoon posing a threat to Earth.
"In most places, lunar gravity at perigee pulls tide waters only a few centimeters (an inch or so) higher than usual," astronomer Tony Phillips wrote in a NASA supermoon alert. "Local geography can amplify the effect to about 15 centimeters (6 inches) — not exactly a great flood."
Meteors from Halley's comet
The supermoon is not the only celestial sight gracing the evening skies this weekend. On Saturday night, the annual Eta Aquarid meteor shower is due to hit its peak, promising up to 60 meteors per hour for skywatchers with optimum viewing conditions (clear weather and away from city lights).
The Eta Aquarid meteor shower is one of two "shooting star" displays created by dust left over by the famed Halley's comet as it makes its 76-year trip around the sun. The Orionid meteor shower in October is the other meteor show from the comet.
While the supermoon is expected to outshine the fainter Eta Aquarid meteors, NASA meteor expert Bill Cooke predicts that some bright fireballs may be visible. Cooke and his observing team at NASA's Marshall Space Flight Center have already recorded several bright fireballs from the Eta Aquarids and are looking forward to seeing more using the agency's network of all-sky meteor cameras.
"Ideal viewing conditions are clear skies away from city lights, especially just before dawn," NASA officials wrote in an Eta Aquarid meteor observing guide. " Find an area well away from city or street lights. Lie flat on your back on a blanket, lawn chair or sleeping bag and look up, taking in as much of the sky as possible. After about 30 minutes in the dark, your eyes will adapt and you will begin to see meteors. Be patient — the show will last until dawn, so you have plenty of time to catch a glimpse."
Views from NASA's all-sky cameras are available to view the Eta Aquarid meteor shower remotely here: http://www.nasa.gov/connect/chat/allsky.html
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