Tuesday, September 23, 2008

How long the solar minimum will last: what statistics say

Solar observers are celebrating a small sunspot from the new cycle that has just appeared - after so many months of low activity even this minute visitor is welcome. But is the current solar minimum really longer than any in recent memory? Indeed it is, an important analysis by Peter Meadows in The Astronomer (45 [Aug. 2008] 99-100) recently showed, but there have been much longer minima in the past centuries. He defines the length of the minimum as the interval when the 13-month average of the international sunspot number falls below 20: These periods have ranged from just one year in 1965 to 8 years in the early 19th century.

The smoothed number fell below 20 in January 2006, and thus the current minimum will last at least 2.5 and perhaps 3.5 years. In any case it is the longest since the one from 1931-35, confirming the suspicions of an unusually long one - on the timescale of a human life, that is. Meadows also finds a moderate correlation between minimum duration and the height of the next peak: expect a moderate one with a maximum smoothed number of 110 to 120. According to Ulysses data, by the way, the solar wind is at a 50-year low: NASA will hold a telecon about that finding later today.

In other news here is an idea about Jupiter's Red Spot Junior color change: "an upward and inward diffusion of either a coloured compound or a coating vapour that may interact later with high energy solar photons." • Comet 29P is in outburst, having risen from 14 to 11.5 mag. • There was an impressive fireball over SoCal on Sep. 19. • A minor planet passed close to Uranus, looking like another moon. • Some images (more, more, more and more) of the Moon vs. the Pleiades on Sep. 20 as seen from Europe. • And image processing seems to reveal blue Earth reflected by the ISS ...

1 comment:

cing said...

^^ nice blog!! ^@^

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