Sunspot Records by Antonio Colla just after the Dalton Minimum

TL;DR

This paper recovers and analyzes 71 sunspot observations by Antonio Colla from 1830-1843, highlighting the value of his records for sunspot counting but cautioning against using his area and position data for scientific analysis.

Contribution

The study uncovers previously unrecognized sunspot records by Antonio Colla, providing new data on sunspot counts during the post-Dalton Minimum period.

Findings

Colla's sunspot counts are comparable to contemporaneous observers.

His drawings reliably indicate the number of sunspot groups.

Sunspot area and position data from his drawings are unreliable.

Abstract

Antonio Colla was a meteorologist and astronomer who made sunspot observations at the Meteorological Observatory of the Parma University (Italy). He carried out his sunspot records from 1830 to 1843, just after the Dalton Minimum. We have recovered 71 observation days for this observer. Unfortunately, many of these records are qualitative and we could only obtain the number of sunspot groups and/or single sunspots from 25 observations. However, we highlight the importance of these records because Colla is not included in the sunspot group database as an observer and, therefore, neither his sunspot observations. According to the number of groups, the sunspot observations made by Colla are similar as several observers of his time. For common observation day, only Stark significantly recorded more groups than Colla. Moreover, we have calculated the sunspot area and positions from Colla's sunspot drawings concluding that both areas and positions recorded by this observer seem unreal. Therefore, Colla's drawings can be interpreted such as sketches including reliable information on the number of groups but the information on sunspot areas and positions should not be used for scientific purposes.