THE GIST
- This Saturday, the moon will come within 221,802 miles from Earth.
- This month's full moon is due to be about 16 percent brighter than average.
Skywatchers take note: The biggest full moon of the year is due to arrive this weekend.
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 skywatchers 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 skywatching 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, Rao said.
The last supermoon occurred in March 2011.
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. ~Discovery
Binocular exploration –see how many lunar seas and craters you can spot. The seas are obvious, while the four most prominent craters labeled at right require only a little extra effort. A huge system of bright rays surround each crater and make them easy to spot. The rays originated when boulders sent aloft from the crater impacts rained back down, striking the moon and creating thousands of mini-craters, each of which excavated fresh soil from the moon’s surface.
Terminator madness – At full moon, the sun, Earth and moon are lined up in that order, and the sun shines squarely on the moon’s face, lighting it up completely. During other phases, we see only part of the moon; the terminator, or day-night line, separates the lit part of the moon from the unlit. At full moon, the terminator essentially disappears because the entire face of the moon is in sunlight. Truth be told, it doesn’t disappear completely. The lineup that I mentioned earlier is exact only in the case of a total lunar eclipse. The moon’s orbit is slightly inclined with respect to Earth’s orbit, so it’s usually a little north or south of the sun-Earth line. Tonight it’s far enough north of that line that telescopic observers will see the terminator running along the south edge of the disk below the prominent crater Tycho. To the naked eye, the moon will appear perfectly circular with no nibbling about the edges. By tomorrow, the terminator will have swung around to its usual post-full moon position on the west side of the disk.
Slip slidin’ away -The difference in the moon’s gravitational pull on the nearside versus the farside of Earth causes the two tidal bulges. Coastal residents are familiar with as the ocean tides. Some of the energy from this moon-Earth interaction causes our planet’s spin to gradually slow down. The spin energy is not wasted, but transferred out to the moon, causing it to move 1 1/2 inches farther from our planet each year. Over several billion years, the Earth’s spin will slow to eventually match the orbital period of the moon. On that far future day, we’ll be locked facing one another so only the inhabitants of the moon-facing side of the Earth will see the moon. Those living on the Earth’s “farside” will have to travel to the other hemisphere for a look-see at the moon. Weird to contemplate, but it’s inevitable. One other consequence of this tug of war is that a more distant moon will also appear smaller, and a smaller moon won’t be able to completely eclipse the sun. The days of the total solar eclipse will be over.
The Earth's tilted axis is stabilized by the moon's gravitational influence.
Thank you for being our friend – One of the wonderful things the moon does for our planet is keep its axial tilt stable. Without the moon, the Earth’s axis would wobble to more extreme tilts like Mars’ axis does, causing catastrophic climate changes. The moon stabilizes our axis and keep our planet’s alignment from going to extremes.
Eminently quotable – You’ll find many mentions of the moon, particularly the full moon, in literature, TV and other media. Here’s a sampling:
“Promises are like the full moon, if they are not kept at once, they diminish day by day.” – German proverb
“Moonlight is sculpture; sunlight is painting.” – Nathaniel Hawthorne
” Everyone is a moon, and has a dark side which he never shows to anybody.” – Mark Twain
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