04 june 2009, 10:10 мск

This year's largest group of sunspots passes across the solar disk

This year's largest group of sunspots passes across the solar disk (observations of the TESIS on CORONAS-PHOTON)
This year's largest group of sunspots passes across the solar disk (observations of the TESIS on CORONAS-PHOTON)

Today this year's largest group of sunspots will cross the Sun's central meridian. The group, registered as number 1019 in the international NOAA catalogue, was literally formed before astronomers' eyes several days ago on the visible side of the Sun. The first two spots appeared on the Sun's surface on May 31st. The next day, the number of spots in the group reached five, and the day after, on June 2nd, it was possible to count thirteen sunspots on solar disk, which had been clear prior to this. All of the spots fitted into an area with a lateral dimension of less than 100 thousand kilometers.

This active beginning to summer has allowed the Sun to beat one of this year's main records; establishing a new maximum Wolf number value - the key parameter of solar activity, based on daily sunspot counts. These counts have been continuously made for over 260 years (the first sunspot counts began in 1749 at an observatory in Zurich). The Wolf number, counted for June 2nd, came to 23. This exceeds the previous maximum for this year by more than twice (on January 11th, the Wolf number reached 10). The last time the index exceeded W=20 was on March 31st, 2008, when the Wolf number reached W=25.

Such a rapid rise in activity did not come as a surprise to astronomers. Observations from space X-ray telescopes show that one of this year's most beautiful active areas, with a very complex magnetic structure, has been developing in this sector of the Sun for several days. What is amazing is its speed of formation. The area appeared from behind the Sun's eastern edge on May 27th, and was already fully formed, although there was no sign of activity either in the solar corona or in the chromosphere two weeks prior, when this sector of the Sun was only beginning to disappear behind the solar horizon.

At the present time, the Sun is very close to setting a three-year record for activity - for this to happen the Wolf number must exceed 40. The last time such a value was observed was on November 3rd, 2006, and now there is another chance of reaching this level. This year's two most powerful active areas, which passed across the solar disk at the beginning of May, 2009, are set to appear in the Sun's eastern sector in two days, on June 6th. The edge of one of these areas is now being observed by the NASA STEREO vehicle, which operates at a significant distance from the Earth and looks behind the edge of the solar disk. TESIS will be able to observe these areas in a day's time and observatories on Earth - in 1-2 days.

It should be noted that all three active areas are now in the Sun's northern hemisphere, or rather in its belt of activity. The south of the Sun seems to have gone into "hibernation", following a short burst of activity. However, the northern belt, which now finally seems to be approaching the growth phase of a solar cycle, also developed in this way.

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