Sunspot observations by Charles Malapert during the period 1618-1626: a key dataset to understand solar activity before the Maunder minimum

TL;DR

This study revises Charles Malapert's sunspot observations from 1618-1626, revealing higher solar activity levels than previously recorded, and provides a key dataset for understanding solar activity before the Maunder minimum.

Contribution

It offers a revised and more accurate account of Malapert's sunspot data, improving the historical solar activity record before the Maunder minimum.

Findings

Revised Malapert's sunspot group counts show 30% higher activity.

Good agreement with other astronomers' observations of the period.

Malapert's records represent a lower limit of solar activity.

Abstract

A revision is presented of the sunspot observations made by Charles Malapert from 1618 to 1626, studying several documentary sources that include those observations. The revised accounting of the group numbers recorded by Malapert for that period shows new information unavailable in the current sunspot group database. The average solar activity level calculated from these revised records of Malapert is by almost one third greater than that calculated from his records included in the current group database. Comparison of the sunspot observations made by Malapert and by other astronomers of that time with regard to the number of recorded groups and sunspot positions on the solar disk shows good agreement. Malapert reported that he only recorded one sunspot group in each sunspot drawing presented in Austriaca Sidera Heliocyclia (the documentary source which includes most of the sunspot records made by Malapert), although he sometimes observed several groups. Therefore, the sunspot counts obtained in this present work on Malapert's sunspot observations represents the lower limit of the solar activity level corresponding to those records.