Friday, 18 March 2011

The story of the super moon: earth's natural satellite at its perigee

Syed Akbar
Hyderabad, March 18: The full moon on Saturday will be 14 per cent bigger and 30 per cent brighter, but those living in urban areas may miss this spectacular celestial sight thanks to light and smoke pollution.

The moon will be at its closest point to the earth on March 19 and astrophysics refer to this phenomenon as "perigee" (in Greek peri means around, and gee means earth). Because of its nearness to the earth by about 50,000 km, the full or super moon will shine 30 per cent brighter. It will be larger than the ordinary full moon by 14 per cent.

While people living in villages will get an opportunity to enjoy the rare beauty of the full moon, unfortunately urbanites may miss the opportunity. "There's the problem of light and other pollution in cities. One can't really make out the difference here. But if one goes away from the city to a rural area, one can really enjoy the beauty of the super moon," Birla Planetarium director Dr BG Siddharth said.

Since the orbit of the moon is elliptical or egg like, the distance between the earth and the moon keeps changing, with the farthest distance (apogee) being 4.06 lakh km and the nearest at 3.56 lakh km. The super moon thus will be about 50,000 km closer to the earth, though in astronomical terms this distance is quite insignificant.

This Saturday's moon will be the biggest in about two decades, the last such super moon happening in March, 1993. The moon was "almost closer" to the earth two years ago, in December, 2008. Super moons occur regularly but a perfect perigee full moon occurring less than one hour away from perigee, happens once in 18 years.

"Astronomically it is not significant. It is not rare either, but if there's no light pollution it will be a beautiful sight worth watching," Dr Siddharth said, adding that though the sea tides may be stronger, they will not cause any damage.

Planetary Society of India general secretary N Sri Raghunandan Kumar says since the moon revolves around the earth in 29.5 days, every month witnesses a perigee and an apogee. But the full moon occurring within an hour of perfect perigee takes place once in many years. The Saturday's moon is one such instance. From India's point of view, ISRO would have sent man into the lunar world by the time the next super moon occurs. ISRO plans to put man on the moon in the next 10 years.

"There's nothing super about this so-called super moon. Actually, astrologer Richard Nile coined the term super moon, giving it astrological connotations. But the super moon has nothing to do with the geological events back on the earth. The best time to watch the celestial spectacle is when the moon is near the horizon," he said.

According to NASA, in most places, lunar gravity at perigee pulls tide waters only a few centimetres (an inch or so) higher than usual. Local geography can amplify the effect to about 15 centimetres (six inches) - not exactly a great flood.

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