Sunspot Observations in 1684-1702: John Flamsteed and Philippe de La Hire

TL;DR

The paper reconstitutes sunspot activity during the Maunder Minimum by systematically curating and reanalyzing Flamsteed and La Hire observations (1684–1702), including drawings and engravings from Cassini and contemporaries. Using VSOP87-based ephemerides and pixel-weighted solar coordinates, the authors reconstruct sunspot positions, areas, latitudes, and group tracks, and estimate sidereal rotation rates from both nearby-day and long-interval methods. The results reveal sunspot latitudes clustered around roughly -10°, rotation rates near 14.0–14.5° per day, and a tendency for Joy's law to be obeyed rather than violated, with notable activity nests and occasional discrepancies due to instrument and orientation effects. The study highlights the value of historical records for calibrating long-term solar indices and for informing models of differential rotation and the solar-cycle behavior during grand minima, while providing openly accessible, digitized data for future work.

Abstract

In this work, we present an extensive review and detailed analysis of sunspot measurements, drawings, and engravings made by John Flamsteed and, mainly, by Philippe de La Hire during the Maunder minimum. All available information and contemporary knowledge about the sunspot nature are shown. The coordinates, areas, and numbers of sunspots and sunspot groups are reconstructed. Based on these observations, La Hire, Jean-Dominique Cassini, and his son Jacques Cassini regularly published results that shed light on the purpose of sunspot measurements and the scientific paradigm of that time. In particular, astronomers believed that sunspots were recurrent over decades. We compare the reconstructed time-latitude diagram with those obtained by Spoerer (Ueber die periodicitat der sonnenflecken seit dem Jahre 1618..., 1889) and Ribes and Nesme-Ribes (Astron. Astrophys. 276, 549, 1993). The sidereal differential rotation rate is estimated, and its latitudinal profile is reconstructed. We also evaluate the fraction of sunspot groups that obey or violate Joy's law.

Figures (13)

• Figure 1: (a) Color-enhanced and $6^{\circ}$-rotated modification of the original engraving from 1684RSPT...14..535F with the heliographic grid and Gregorian dates imposed. The Equator position from 7 June is marked in blue. The black square on the top center is the original engraving of the sunspot scaled and oriented with the grid. (b) and (c) Sunspot latitudes deduced from the engraving. The latitude calculated by 1684RSPT...14..535F on 6 May is shown with a black asterisk. (d) and (e) The longitudes deduced from the engraving and that calculated by 1684RSPT...14..535F (asterisk). The gray shaded area illustrates the expected longitudes at a rotation rate of $14.26^{\circ}$ d$^{-1}$.
• Figure 2: (a) Sunspot position derived from measurements in Flamsteed_1712 in blue and 1684RSPT...14..535F in red. Reliable data are represented by filled circles, whereas unreliable data are shown as unfilled circles. The blue rectangle and annular sector show the range of possible sunspot locations. The heliographic grid corresponds to the equatorial setup of a telescope. (b) Sunspot longitudes and rotation rate deduced based on reliable data.
• Figure 3: Sunspot drawings and engravings from 5 to 9(!) May 1684: (a -- f) from La_Hire_1683_1684 and (g) Monnier_1741.
• Figure 4: (a) Sunspot position derived from the measurements by La_Hire_1683_1684 from 5 May to 28 July 1684. Reliable data are represented by filled circles, whereas unreliable and incomplete data are shown as unfilled circles and annular sectors. The heliographic grids correspond to the equatorial mount. (b) Sunspot longitudes and rotation rate.
• Figure 5: Visualization of sunspot transits reconstructed from the measurements and sunspot drawings by La_Hire_1683_1684. Yellow denotes faculae. Black circles indicate objects with the size of $30"$ and $40"$. The orange sunspot out of the solar disk reproduces the horizontally and vertically mirrored sunspot engraving from the Journal des Sçavans (Scavans_1684).