NEW YORK, Mar. 20, 2011 (Reuters) — An especially large moon will appear to rise on Saturday in the most extreme example of a so-called super-moon phenomenon in nearly 20 years, according to the U.S. Naval Observatory.
For such a visible super-moon to be visible, the moon must be full and passing through its closest approach to earth, known as the perigee, in its month-long, elliptical orbit, the Observatory said on its web site.
This perigee is the closest one for the entire year, the Observatory said.
While less spectacular super-moons occur several times a year, Saturday's is the best example of a perigee-syzygy, to use astronomers preferred term, since March 8, 1993, it said.
The effect may be at its most striking as the moon is rising and still close to the horizon, it said.
A common belief that a super-moon can cause flooding through its impact on tides is incorrect, according to the National Oceanic and Atmospheric Administration, which said tidal ranges typically increase at most by a negligible couple of inches.
(Reporting by Jonathan Allen, editing by Ellen Wulfhorst)
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