The solar differential rotation in the 18th century

Abstract

The sunspot drawings of Johann Staudacher of 1749--1799 were used to determine the solar differential rotation in that period. These drawings of the full disk lack any indication of their orientation. We used a Bayesian estimator to obtain the position angles of the drawings, the corresponding heliographic spot positions, a time offset between the drawings and the differential rotation parameter δΩ, assuming the equatorial rotation period is the same as today. The drawings are grouped in pairs, and the resulting marginal distributions for δΩwere multiplied. We obtain δΩ=-0.048 \pm 0.025 d^-1 (-2.75^o/d) for the entire period. There is no significant difference to the value of the present Sun. We find an (insignificant) indication for a change of δΩthroughout the observing period from strong differential rotation, δΩ\approx -0.07 d^-1, to weaker differential rotation, δΩ\approx-0.04 d^-1.

6 pages, 6 figures, accepted for Astronomy and Astrophysics

References in corpus (1)

• The butterfly diagram in the 18th century

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• Sunspot Drawings by Japanese Official Astronomers in 1749-1750
• Bošković's method for determining the axis and rate of solar rotation by observing sunspots in 1777
• The solar rotation in the period 1853-1870 from the sunspot catalogues of Carrington, Peters, and de la Rue
• Bošković's Spherical Trigonometric Solution for Determining the Axis and Rate of Solar Rotation by Observing Sunspots in 1777