Analyses on Wassenius' Report for Total Solar Eclipse in 1733: Quantifications of the Solar Radius and the Earliest Reported Prominences

TL;DR

This study analyzes Wassenius' 1733 report on the total solar eclipse, quantifying the solar radius and prominences, and discusses implications for solar minimum timing and prominence classification.

Contribution

It translates Wassenius' original report, provides precise measurements of the solar radius from 1733, and links prominence observations to solar activity phases.

Findings

Measured solar radius during 1733 eclipse closely matches modern values.

Reported prominences at high latitudes suggest a solar minimum around 1733.

Classified prominences as quiescent, indicating early polar magnetic activity.

Abstract

Total solar eclipses (TSEs) offer a unique opportunity to observe the solar atmosphere, detect limb phenomena, and accurately measure the solar radius. Following the TSE in 1733, Wassenius first reported the existence of prominences to the scientific community. Wassenius' original manuscript is held in the Royal Academy Archives of Sweden; this study translates his report and documents the associated source materials and local eclipse visibility. The solar radius (R_Sun) during the TSE in 1733 are 696250 +/- 170 km and 959.99 +/- 0.24" in the absolute and apparent scales, respectively. This result contrasts with the modern standard (helioseismic) R_Sun of 695780 +/- 160 km and 959.34 +/- 0.22"; however, it is consistent with the solar radius recorded in 1715. The observed prominences are located at +23.5 +/- 22.5{\deg}, +66.5 +/- 22.5{\deg}, and -68.5 +/- 22.5{\deg} in the heliographic latitude. The appearance of prominences at such high latitudes contrasts with the sunspot butterfly diagram for 1725-1750, confirming 1733 as a solar minimum. These high-latitude prominences can potentially be attributed to the so-called 'polar rush' prominences that appear a few years after a solar minimum. If they are categorised as 'polar rush' prominences, the solar minimum must be re-dated to before 1733 May. Furthermore, the latitudes of at least two of the prominences reported by Wassenius enable their classification as quiescent prominences, suggesting the presence of a polarity inversion line in the polar regions in early 1733.