The moon will officially become full Saturday (May 5) at 11:35 p.m. EDT. And because this month's full moon coincides with the moon's perigee its closest approach to Earth it will also be the year's biggest. The moon will swing in 221,802 miles (356,955 kilometers) from our planet, offering sky watchers a spectacular view of an extra-big, extra-bright moon, nicknamed a supermoon. And not only does the moon's perigee coincide with full moon this month, but this perigee will be the nearest to Earth of any this year, as the distance of the moon's close approach varies by about 3 percent, according to meteorologist Joe Rao, SPACE.com's sky watching columnist. This happens because the moon's orbit is not perfectly circular.

This month's full moon is due to be about 16 percent brighter than average. In contrast, later this year on Nov. 28, the full moon will coincide with apogee, the moon's farthest approach, offering a particularly small and dim full moon. Though the unusual appearance of this month's full moon may be surprising to some, there's no reason for alarm, scientists warn. The slight distance difference isn't enough to cause any earthquakes or extreme tidal effects, experts say. However, the normal tides around the world will be particularly high and low. At perigee, the moon will exert about 42 percent more tidal force than it will during its next apogee two weeks later. To view this weekend's supermoon to best effect, look for it just after it rises or before it sets, when it is close to the horizon. There, you can catch a view of the moon behind buildings or trees, an effect which produces an optical illusion, making the moon seem even larger than it really is.

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 higher than usual,” astronomer Tony Phillips wrote in a NASA supermoon alert. “Local geography can amplify the effect to about 15 centimeters not exactly a great flood.” The word supermoon didn’t come from astronomy. Instead, it came from astrology. Astrologer Richard Nolle of the websiteastropro.com takes credit for coining the term supermoon. May 2012 presents the moon’s closest encounter with Earth since March 19, 2011, at which time the moon was a scant 380 kilometers closer to Earth. The moon won’t come as close as tonight’s extra-close moon until August 10, 2014 although in 2013 the moon at its closest June 23, 2013 will lie only 36 kilometers farther away than the closest moon in 2012. Maybe this helps you see that supermoon while interesting are fairly routine astronomical events.