Super-sizing the moon

Three perigee, or "super" full moons occur this summer - Saturday, Aug. 10 and Sept. 9.

On average a full moon occurs near perigee every 13 1/2 months.

Because the moon's orbit makes it change "size" daily, scientists first calculated the orbit by taking photographs and comparing measurements. Today they do it with radar and lasers.

Even though the moon appears larger on the horizon, the positioning makes it measure a little smaller.

Sources: NASA, Terry Richardson

Here it comes, another really, really BIG moon. A "super" full moon rises just about sunset Saturday, the first of three this summer.

How big? Well, about as big as the three that occurred last year - 14 percent larger and 30 percent brighter than usual. And frankly, not as large as the supermoon in August will be. That one will be "almost the biggest possible moon you could have," said College of Charleston astronomer Terry Richardson.

Now you're talking. Supermoons appear when the moon is at perigee, or a point closest to earth in its oval-shaped orbit, according to NASA. The moon on Aug. 10 will become full within an hour of making its closest approach to our planet, "arguably making it an extra-super moon," according to the NASA release.

Pretty exciting stuff, huh? Not so much. Most times, a perigee moon in the sky isn't noticeably larger unless you're looking for it. Of the three that occurred last year, only one was paid much attention.

When people are expecting a big moon, they tend to latch onto the "moon illusion," a not-so-completely-understood phenomenon that makes the moon appear larger as it rises and sets.

"I guarantee that some folks will think (the August moon) is the biggest they have even seen if they catch it rising over a distant horizon because the media will have told them to pay attention to this one," said Geoff Chester, of the U.S. Naval Observatory. But for astronomers, the occurrence just isn't special.

"It's kind of neat," Richardson said, mostly because it gets people interested in celestial mechanics.

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