Due to the weather, some customers may experience late delivery of The Roanoke Times. We apologize for the delay.
Sunday, May 26, 2013
Supermoon. The name foretells something spectacular coming our way. Surely, it must be special and probably rare. You be the judge.
The recent full moon, as bright as it was, was not a supermoon. However, our next full moon, the one found glowing brightly on the night of June 22 into the following morning, will be. It will be the brightest full moon of 2013. By itself, this does not qualify it as a supermoon.
The moon revolves around our planet following an elliptical path, resulting in it, at times, lying comparatively close to Earth, while, at other times, being relatively far away. At its closest approach, known as perigee, the moon averages about 229,000 miles from Southwest Virginia, and when it reaches its farthest point, known as apogee, it averages 250,000 miles from us. These two values averaged together give the commonly quoted Earth-moon distance of 240,000 miles.
When at a typical perigee, the moon’s apparent diameter is 9 percent wider than at apogee, because it is 9 percent closer. It also covers 19 percent more area in the sky. When the full moon occurs at perigee these values increase, appearing 14 percent wider and nearly 30 percent greater in both area and brightness than when it happens at apogee. This creates a supermoon.
As with many orbital phenomena in the solar system, the ultimate cause for the supermoon rests with the sun’s immense gravitational field. A full moon occurs when the moon, Earth, and sun lie ordered in a straight line. If this alignment occurs when the moon is also at perigee, its closest point to Earth, the sun’s gravity pulls the moon slightly closer toward it and Earth, making this perigee closer than average. The full moon appears consequently larger and brighter in our night sky, producing a supermoon.
If, instead, the moon reaches apogee when it is full, the sun’s grip on it is somewhat lessened since it moves slightly farther from the sun. The apogee full moon then appears slightly smaller and glows less brightly in our night sky. Since this doesn’t warrant people’s attention, or the media’s, there is no term for this condition. Why not call it a “submoon?”
How often does a supermoon (or submoon) occur? The period between successive full moons is 29.5 days and that between perigees is 27.6 days. It turns out that the time between every 14 full moons is almost equal to the time between 15 perigees, or about 413 days. So, there is about one year, one month and 18 days between supermoons. The last one of these special full moons occurred on May 5, 2012, and the next one comes on August 10, 2014.
The supermoon of May 5, 2012, created a media stir. As you can see, though, these special moons aren’t particularly rare or unusual. Will any media attention be warranted for the June 22-23 event? Only you can be the judge.
Weather JournalSo ... WHERE is this storm?