A solar cycle lost in 1793--1800: Early sunspot observations resolve the old mystery

TL;DR

This study uses newly recovered 18th-century sunspot drawings to identify a previously unrecognized solar cycle starting in 1793, resolving a long-standing mystery and suggesting revisions to historical solar activity records.

Contribution

It provides the first direct evidence of a solar cycle in 1793 using historical sunspot drawings, challenging traditional sunspot series and improving understanding of solar cycle timing.

Findings

Identification of a new solar cycle starting in 1793

Confirmation of the existence of a lost solar cycle in the late 18th century

Implications for solar cycle statistics and solar activity models

Abstract

Because of the lack of reliable sunspot observation, the quality of sunspot number series is poor in the late 18th century, leading to the abnormally long solar cycle (1784--1799) before the Dalton minimum. Using the newly recovered solar drawings by the 18--19th century observers Staudacher and Hamilton, we construct the solar butterfly diagram, i.e. the latitudinal distribution of sunspots in the 1790's. The sudden, systematic occurrence of sunspots at high solar latitudes in 1793--1796 unambiguously shows that a new cycle started in 1793, which was lost in traditional Wolf's sunspot series. This finally confirms the existence of the lost cycle that has been proposed earlier, thus resolving an old mystery. This letter brings the attention of the scientific community to the need of revising the sunspot series in the 18th century. The presence of a new short, asymmetric cycle implies changes and constraints to sunspot cycle statistics, solar activity predictions, solar dynamo theories as well as for solar-terrestrial relations.