Newly found sunspot observations by Peter Becker from Rostock for 1708, 1709, and 1710

TL;DR

This paper uncovers and analyzes newly found historical sunspot observations from 1708-1710, providing new data on solar activity during the end of the Maunder Minimum and enhancing the historical sunspot record.

Contribution

It presents previously unknown sunspot observations from Peter Becker and G. Kirch, including detailed drawings and measurements, enriching historical solar activity data.

Findings

New sunspot locations and sizes for 1708-1710

Revised sunspot group numbers for the period

Enhanced understanding of solar activity recovery post-Maunder Minimum

Abstract

We present a few newly found old sunspot observations from the years AD 1708, 1709, and 1710, which were obtained by Peter Becker from Rostock, Germany. For 1709, Becker gave a detailed drawing: he observed a sunspot group made up of two spots on Jan 5, 6, and 7, and just one of the two spots was observed on Jan 8 and 9. We present his drawing and his explanatory text. We can measure the latitude and longitude of these two spots and estimate their sizes for all five days. While the spots and groups in 1708 and the spot on four of the five days in January 1709 were known before from other observers (e.g. Hoyt & Schatten 1998), the location of the spots in early January 1709 were not known before, so that they can now be considered in reconstructed butterfly diagrams. The sunspots detected by Becker on 1709 Jan 5 and 1710 Sep 10 were not known before at all, as the only observer known for those two dates, La Hire, did not detect that spot (group). We estimate new group sunspot numbers for the relevant days, months, and years. The time around 1708--1710 is important, because it documents the recovery of solar activity towards the end of the Maunder Grand Minimum. We also show two new spot observations from G. Kirch for 1708 Sep 13 \& 14 as described in his letter to Wurzelbaur (dated Berlin AD 1708 Dec 19).