Bay City News Service—Astronomers are encouraging people to take a moment to observe the moon on Saturday night, May 5, when it will appear bigger and brighter than normal in what's known as a "super moon."
The moon will appear roughly 14 percent larger and 30 percent more luminous than most full moons because it will be about 50,000 miles closer than its farthest point in its elliptical orbit, according to NASA.
The moon will reach perigee, or the part of its orbit closest to Earth, at 8:34 p.m. and will align with the sun one minute later, appearing even more resplendent, according to NASA.
The super moon, or "perigee moon," last occurred on Mar. 19, 2011, but Alan Gould, the associate director of the Lawrence Hall of Science planetarium in Berkeley, said that this year's super moon is slightly smaller than last year's event.
"The one this year is just a tiny, tiny bit smaller than the one of last year," Gould said, because of fluctuations in the moon's orbit, which is inclined relative to the plane of the Earth's orbit around the sun. "It's not really any difference that you can actually see, you can barely measure it even," he said.
Gould noted that the super moons may occur annually during this 18.6-year lunar nodal cycle, but that the largest of the super moons occurs once during those nearly 19 years. Prior to last year, the previous maximum super moon was visible in 1993. Following that schedule, the next such major super moon will occur in 2029.
Other than its visual impacts, a super moon also creates especially exaggerated tides known as "perigean tides," with tidal waters rising about an extra inch, according to the National Oceanic and Atmospheric Administration.
Scientists say that the best time to observe the super moon is when the moon is near the horizon, during either moonrise or moonset. At those points, the moon appears much larger than normal, as objects in the foreground provide references for estimating the moon's size, opposed to when the moon is high in the vast sky.
Gould said this "moon illusion" is nothing explained by physics but is instead a matter of the mind. "It's almost like an optical illusion," he said.
The Lawrence Hall of Science is not holding any event to mark the celestial occasion, but visitors are welcome to go to the hall's outdoor plaza to observe the night skies, according to a hall representative.
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