The Paris Observatory is in possession of a 53 y record of solar diameters and sunspot positions during the Maunder minimum (1666 - 1719). For the period 1666 to 1684, the solar diameter was 32arcmin9arcsec and slowly decreased down to 32arcmin6arcsec when sunspot activity had resumed. Nowadays, the solar diameter is 32arcmin2arcsec. During the same period, the sunspot rotation was smaller than the present one and the differential rotation was greater. The two phenomena suggest that the Sun undergoes a cyclic expansion and contraction.
Advances in Helio- and Asteroseismology
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