Sunspot positions from observations by Flaugergues in the Dalton Minimum

Abstract

French astronomer Honoré Flaugergues compiled astronomical observations in a series of hand-written notebooks for 1782–1830, which are preserved at Paris Observatory. We reviewed these manuscripts and encoded the records that contain sunspot measurements into a numerical table for further analysis. All measurements are timings and we found three types of measurements allowing the reconstruction of heliographic coordinates. In the first case, the Sun and sunspots cross vertical and horizontal wires, in the second case, one vertical and two mirror-symmetric oblique wires, and in the third case, a rhombus-shaped set of wires. Additionally, timings of two solar eclipses also provided a few sunspot coordinates. As a result, we present the time–latitude (butterfly) diagram of the reconstructed sunspot coordinates, which covers the period of the Dalton Minimum and confirms consistency with those of Derfflinger and Prantner. We identify four solar cycles in this diagram and discuss the observed peculiarities as well as the data reliability.

Karl von Lindener’s sunspot observations during 1800–1827: Another long-term dataset for the Dalton Minimum

“…Figure 7 also confirms more sunspot groups in the northern solar hemisphere over Solar Cycle 6. This trend is consistent with the butterfly diagrams reconstructed from manuscripts of Prantner and Flaugergues (Hayakawa et al, 2021a;Illarionov & Arlt, 2023) and contrasted with those of the Maunder Minimum (Ribes & Nesme-Ribes, 1993;Vaquero et al, 2015b;Hayakawa et al, 2021bHayakawa et al, , 2021c.…”

“…2024, 13, 33 group positions from Schwabe (Senthamizh Pavai et al, 2015). Figure 6 confirms von Lindener's sunspots in both solar hemispheres, following other contemporary sunspot observers' data (Hayakawa et al, 2020b(Hayakawa et al, , 2021aIllarionov and Arlt, 2023). This result contrasts the Dalton Minimum with the Maunder Minimum (Ribes & Nesme-Ribes, 1993), unlike some claims that classify both of them as the same solar-activity categories (Zolotova & Ponyavin, 2015).…”

“…Therefore, we had to revise them to spotless days. Although sunspots were active around 1802, neither Derfflinger nor Flaugergues reported them during this period (Hayakawa et al, 2020a;Illarionov & Arlt, 2023). However, we can also accommodate another scenario in which von Lindener depicted empty disks for his observation days but eventually failed to fill these solar disks for an undocumented reason.…”

“…Recent studies have added several short-term observers overlooked in the existing databases (Denig & McVaugh, 2017;Hayakawa et al, 2018;Carrasco et al, 2018). Furthermore, recent studies have examined original manuscripts from several long-term observers' records around the DM, especially those of Thaddäus Derfflinger in 1802-1824 (Hayakawa et al, 2020a), Stefan Prantner in 1802-1844 (Hayakawa et al, 2021a), Cornelis Tevel in 1816-1836 (Carrasco, 2022), and Honoré Flaugergues in 1782-1830 (Illarionov & Arlt, 2023). These results significantly improved the sunspot group number and confirmed sunspot distributions in both hemispheres during DM (as a secular minimum), in contrast to the MM (as a grand minimum).…”