One limitation, related to the failure of Blackett's theory, is that any electric circuit rotating like a solid body will not produce "dynamo currents." Even if part of the circuit follows the axis of rotation, and can therefore be viewed as non-rotating, solid rotation will not create any currents. An essential feature of the Faraday disk dynamo is that part of its circuit is outside the disk, not sharing its rotation.

    The rotation of the Sun around its axis, therefore, does not by itself contribute to its magnetism. What is important in this case is that the Sun does not rotate like a solid ball. Its equator has a shorter rotation period than higher latitudes-- about 25 days for the equator, 27 days for latitude 40 degrees (the Earth meanwhile moves some distance around the Sun, so from here the period seems to be 27 and 29 days). If Earth rotated that way, Florida (for instance) would soon pull away from the rest of the US, into the Atlantic Ocean. Such an uneven motion, deforming the surface, can drive a dynamo, and in the Sun's case, it is indeed believed to be the source of sunspot magnetism.

Posted by Jay Roberts at 02:16 AM | Permalink