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Since 1st March, 1999
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Blot on sun, as big as 7 earths
An artistís conception of the European Space Agencyís Huygens Probe as it descends to Saturnís moon Titan. (Reuters)

Calcutta/New Delhi, Jan. 14: In three days, an invisible speck on the sun has swollen to a giant shadow, the size of seven earths.

The dark side of the sun was visible today even to the shortsighted human eye. Bathers taking the holy dip in the Hooghly on the morning of Makar Sankranti were taken aback to see a sullied sun.

In this season of unusual ' and disastrous ' natural phenomena, they were a little afraid, too. After all, it was only yesterday that Saturn could be spotted creeping close to the earth.

'We received at least 20 phone calls in the morning about spots on the sun visible to the naked eye,' said Debiprosad Duari, director, research & academics, MP Birla Planetarium in Calcutta.

'With solar filters, we observed and found an exceptionally large sunspot at almost the centre of the sun.'

Can it cause misery on the face of this already ravaged earth' It can but so far it hasn't.

Sunspots are relatively cool dark spots appearing periodically in groups on the surface of the sun that are associated with strong magnetic fields. 'These spots are caused due to high magnetic field activity on the sun,' said Duari. 'They are generally not visible to the naked eye but in this case the size of the sunspot allowed that.'

They can trigger flares ' or bursts of high-energy X-rays and particles ' which can travel to the earth and cause magnetic storms, disrupting satellite and terrestrial communication.

The US Space Environment Centre today upgraded the sunspot dubbed No. 720 as a 'beta-delta' type, which, scientists say, has the potential to trigger disruptive flares.

What is a sunspot: A relatively cool, dark spot appearing on the sunís surface periodically
Why this one is special: Sunspots this big ó seven times the size of earth ó occur rarely
What can happen: Disturbance in radio communication, high-altitude flight communication and high-voltage power transmission

'Delta sunspots are known to cause flares that affect communications on earth,' said Parameswaran Venkatakrishnan, director of the Udaipur Solar Observatory.

No. 720 started growing since January 11. 'But it was only yesterday and today that it began developing rapidly till it acquired the giant size,' Duari said.

The sunspot may continue to grow or disintegrate into smaller spots.

Don't try to watch what happens, though. An astronomer warned that peering at the sun even in the early morning or late in the evening could damage the eyes. 'It's never safe to observe sunspots directly,' said Nandivada Rathnasree, the director of the Nehru Planetarium in New Delhi.

Sunspot 720 has formed at a time when the sun is approaching the nadir of the 11-year solar cycle marked by an increase and decrease in sunspot activity. The last maximum sunspot activity occurred about five years ago, and the next maximum is expected in 2011.

'But it's not unusual for a large sunspot to appear at this time,' Venkatakrishnan said.

An international space weather forecast issued early Friday said there was a 60 per cent probability that an M-class solar flare would occur in the next 48 hours. An M-class flare is a medium-sized event that may cause partial communication disruption.

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