An auroral and unusually big supermoon' was seen lighting up the sky on Saturday, offering a visual treat to an enthusiastic audience of curious sky-gazers.

The phenomenon was special, as the moon came closest to the earth in 18 years, becoming the biggest and brightest full moon of the year. The moon was around 14 per cent bigger and 30 per cent brighter than the other full moons, Nehru Planetarium Director N. Rathnasree said.

The supermoon' is the biggest and brightest of 2011, C.B. Devgun, director of the Science Popularisation Association of Communicators and Educators (SPACE), told PTI.

The moon was only 3,56,577 km away. The phenomenon occurred in 1955, 1974, 1992 and 2005.

Full moons coinciding with the moon's closest point to the earth in fact happen after every one year, one month and 18 days when it is about 3,63,104 km from the earth, Mr. Devgun said. This is because the moon's orbit is an ellipse, with one side 50,000 km closer to the earth than the other. In astronomy, the two extremes are called apogee' [far away] and perigee' [nearby].

A public sky-watch with telescopes and a live show with full dome visuals were organised by the Nehru Planetarium on Saturday evening for sky-gazers to have a better view of the perigee full moon, Ms. Rathnasree said. Hundreds of people thronged the planetarium to see the earth's natural satellite, she said, adding it was totally safe to watch the moon with naked eyes.

Dispelling reports that a correlation existed between the moon and earthquakes, she said the data for the past 100 years and more showed no correlation.

It is meaningless to equate the supermoon' with earthquake or tsunami. No inference should ever be drawn from looking at just two data points; any statistical correlation has to be checked over a number of data points.

Earthquakes and tsunami were earth's internal affairs, R.C. Kapoor, a retired professor of the Indian Institute of Astrophysics said. The moon could cause a higher tide and nothing else.

The term supermoon' was first coined by astrologer Richard Nolle in 1979. He defined it as a situation in which the moon is slightly closer to the earth on its orbit than the average, which is 90 per cent or more of its closest orbit, and the moon is a full or new moon.

At the closest, the moon lies roughly 3,56,630 km from the earth.