Strong evidence of low levels of solar activity during the Maunder Minimum

TL;DR

This study provides strong evidence that solar activity during the Maunder Minimum was very low, based on detailed analysis of sunspot data from 1709, surpassing previous estimates of activity levels.

Contribution

The paper introduces a new analysis of Muller’s sunspot observations from 1709, establishing a robust lower bound on solar activity during the Maunder Minimum.

Findings

Solar activity in 1709 was lower than during the Dalton Minimum.

The analysis sets an upper threshold for active day fraction in 1709.

Results confirm very low solar activity levels during the Maunder Minimum.

Abstract

The Maunder Minimum (MM) was a period of prolonged solar activity minimum between 1645 and 1715. Several works have identified a significant number of problematic spotless days in the MM included in existing databases. We have found a list of exact spotless (in the second half of 1709) and spot days (January and August 1709) provided by Johann Heinrich Muller. We computed the most probable value and upper/lower limits of the active day fraction (ADF) from Muller's data using the hypergeometrical probability distribution. Our sample is not strictly random because Muller recorded observations in consecutive days when he observed sunspots. Therefore, our result represents an upper threshold of solar activity for 1709. We compared this result with annual values of the ADF calculated for the Dalton Minimum and the most recent solar cycles. We concluded that it was less active than most years both in the Dalton Minimum and in the most recent solar cycles. Therefore, the solar activity level estimated in this work for 1709 represents robust evidence of low solar activity levels in the MM.