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Thursday, May 3, 2012

Good Moon Rising

The moon exerts a gravitational pull on the waters of the earth, whether it be in plants or in the oceans. This can affect the flavor of fruits -- even coffee! -- and can certainly influence floods in low-lying coastal areas. Because we do not understand all of the possible effects of tides, people sometimes worry about the effects the moon --especially a full moon -- might have. A special full moon, such as the "super moon" expected on Saturday night, May 5, can lead to more intense concerns.

The images below compare the apparent size of the moon at perigree and apogee. Of course, the moon does not actually change size or brightness; it just looks that way to observers at the earth's surface.
As explained by National Geographic, a super moon occurs when the moon achieves its full phase at the same time it has its closest approach (perigree) to the earth in a given year. This will occur Saturday night, and in fact the two events (full moon and close approach) will occur within minutes of each other near midnight. Just as it reaches the full phase, the moon will be only 356,955 kilometers away, compared to its average distance of 384,400. The result is that the moon will appear to be 16 percent larger and 30 percent brighter than average.

Because the moon appears largest when it is near the horizon, the best time for photographers to take advantage of the "super moon" will be just after sunset, as the moon is rising. If you go out to observe the moon at this hour, notice that the sun will have just set exactly opposite of where you see the moon rise!

And finally: do not worry! The impacts of this coincidence will be limited to tides and possibly fruits!

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