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The Next 11-Year Solar Cycle Begins

    Naturevolume 155page15 (1945) | Download Citation



    THE recent appearance of a big sunspot (visible at times to the unaided eye), together with four or five smaller groups overlapping in time, probably signifies that the rise in solar activity towards its next maximum has now definitely begun. This major group of spots in south latitude 22° crossed the sun's disk between December 8 and 20 last, the time of central meridian passage being December 14·3. A considerable disturbance in the earth's magnetic field occurred on December 16–17, with associated disturbed conditions for long-distance radio communication. For the past eighteen months, high latitude (20°–40°) sunspots have begun to appear in increasing numbers, giving the characteristic overlap seen at this epoch of the 11-year cycle with the decreasing old-cycle spots in equatorial latitudes (0°–10°). The routine observations of the magnetic fields of sunspots, carried out at the Mount Wilson Observatory (Proc. Ast. Soc. Pacific, Oct. 1944) show that the anticipated reversal of the magnetic polarity of comparable sunspots has taken place with the appearance of the new cycle spots, as first observed by Hale at the sunspot minimum of 1913. Sunspot frequency during 1943–44 gives a minimum at about 1944·5. The rise from minimum to the following peak of the cycle takes on the average 3½–4 years; but individual cycles vary in amplitude and time of phase, not subject to prediction.

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