Analyses for graphical records for a total solar eclipse in May 1230: a possible reference for the “Medieval Grand Maximum”

Abstract

Abstract Datable graphical records of total solar eclipses allow us to assess contemporaneous variability of Earth's rotation speed, solar coronal structure, and solar-wind conditions. Such records are known back to the early 18th century. Here, we examine Matthew Paris’ medieval manuscript, an eyewitness account of a total solar eclipse just after local sunrise, and analyse his eclipse drawings on 14 May 1230. We philologically identify his observational site as St. Albans and compute local eclipse visibility. To locate St. Albans in the totality path, our analysis requires ΔT in 555 s < ΔT < 923 s (loose scenario), consistent with the latest published ΔT spline curve, which indicates that only the upper part of the eclipsed Sun should have been visible in this case. The eclipsed Sun sould have been entirely visible over the local horizon if we set the ΔT margins to 555 s < ΔT < 571 s (strict scenario), which requires slightly modifying the latest ΔT spline curve. Matthew Paris’ drawing of the total solar eclipse showed streamer-like structures similar to solar-minimum-type coronal streamers, consistent with the local tilt of the apparent solar equator. This is morphologically consistent with the minimum-type solar coronal streamers predicted from the open solar flux reconstructed from the 14C dataset. This record potentially demonstrates a similarity in solar cycles between the ‘Medieval Grand Maximum’ and modern solar cycles. Collectively, historical eclipse records could be used to assess Earth's rotation speed, solar coronal dynamics, and background solar dynamo activity on a millennial timescale.