Supermoon Saturday: Why it's the biggest, brightest of 2012 (+video)
Supermoon Saturday: It's also called the 'Flower Moon,' and 'Milk Moon.' The 'supermoon' will be only 221,802 miles from Earth, the closest to our planet this year.
On Saturday (May 5) at 11:35 p.m. EDT, the moon will officially turn full. And only 25 minutes later the moon will also arrive at perigee, its closest approach to Earth — a distance of 221,802 miles (356,955 kilometers) away.
The effect of this coincidence is a stunning skywatching sight called the "supermoon."
In fact, this month's perigee is the closest of any perigee in 2012 (they vary by about 3 percent, because the moon's orbit is not perfectly circular). The result will be a 16 percent brighter-than-average full moon accompanied by unusually high and low tides this weekend and into the new week.
In contrast, later this year, on Nov. 28, the full moon will closely coincide with apogee, the moon's farthest point from Earth. [Amazing Supermoon Photos from 2011]
Every month, "spring" tides occur when the moon is full and new. The word "spring," in this case, is derived from the German springen, to "spring up," and is not — as is often mistaken — a reference to the spring season. At these times the moon and sun form a line with Earth, so their tidal effects add together. The sun, because of its distance, exerts a little less than half the tidal force of the moon.
"Neap" tides, on the other hand, occur at those times when the moon is at first and last quarter and work at cross-purposes with the sun. At these times, tides are weak.