A CLOSER LOOK: Comet Schwassmann/ Wachmann 3, picture courtesy NASA

Eclipses come and go. But here?s astronomical phenomenon as rare as it gets.

Calcuttans, along with people from around the world, will get the opportunity to watch a comet ? and its disintegrated pieces ? come as close as 11 million km to earth, in the night sky this weekend.

Comet Schwassmann/Wachmann 3 was discovered in Germany by Arnold Schwassmann and Arno Arthur Wachmann in 1930. The comet disappeared for a while and resurfaced in the 1970s.

In 1995, the comet was found broken into three pieces. ?According to observations through Hubble and other big telescopes, the comet now has at least eight pieces,? said Debiprosad Duari, director (research & academics) of MP Birla Planetarium.

During May 11 to 13, Schwassmann/Wachmann 3 will come as close to earth as any comet has in the past 20 years.

?It will be dimly visible with the naked eye, but a powerful binocular or a three to four-inch telescope should help,? Duari said.

The comet can be best observed by those in and around Calcutta on the night of May 12, 9.30 pm onwards, at 30 degrees east of north in the constellation of Cygnus. At 12.30 am, it will be 40 degrees above the horizon.

?The phenomenon is rare because the splitting up may continue and the comet may cease to exist, as in the case of the comet Biela, which started disintegrating in 1846 and vanished in 1872,? Duari offered.

A comet is made up of dry ice, frozen methane, ammonia and dust. When it comes close to the sun during its journey, the ice begins to evaporate, leaving a spectacular tail millions of km long.

The comet may disintegrate when its icy nucleus breaks by the thermal stress due to its proximity to the sun. It may also disintegrate on collision with another small solar system body. ?Debris from the disintegration may expand slowly and cause a meteor shower over earth,? Duari added.

But bad news for Doomsday forecasters ? there?s hardly any possibility of the comet posing a threat to the life and environment of the earth.