Abstract
We discuss the significant implications of three eye-witness drawings of the total solar eclipse on 1706 May 12 in comparison with two on 1715 May 3, for our understanding of space climate change. These events took place just after what has been termed the “deep Maunder Minimum” but fall within the “extended Maunder Minimum” being in an interval when the sunspot numbers start to recover. Maria Clara Eimmert’s image in 1706 is particularly important because she was both a highly accomplished astronomical observer and an excellent artist: it was thought lost and was only re-discovered in 2012. Being the earliest coronal drawings of observational value yet identified, these drawings corroborate verbal accounts a corona without significant streamers, seen at totality of this and another eclipse event in 1652 during the Maunder Minimum. The graphical evidence implies that the coronal solar magnetic field was not lost but significantly weakened and the lack of coronal structure means there was little discernable open flux (either polar or at lower latitudes) even during the recovery phase of the Maunder Minimum. These observations provide evidence for a different state of oscillation of the solar dynamo, and hence behaviour of the Sun, in comparison with that during normal solar cycle minima (when a streamer belt between two polar coronal holes is visible) or near normal sunspot maxima (when coronal structure is caused by coronal holes at all latitudes) even to observers without a telescope.
Highlights
In addition to the regular Schwabe cycles of 11 years duration, solar activity has a longer-term and wider variability between the grand minima and grand maxima (Steinhilber et al, 2010; Hathaway, 2015; Usoskin, 2017)
We confirm a striking contrast of the coronal structure between the eclipses in 1706 without significant radial streamers in the late MM and 1715 with crossshape streamers immediately after the MM
The corona without significant radial streamers in the late MM is interpreted as: either (1) the F-corona was brighter than the K-corona at all distances from the Sun; or (2) open flux decayed significantly, sufficient to make it incapable of inducing structure in a K-corona
Summary
In addition to the regular Schwabe cycles of 11 years duration, solar activity has a longer-term and wider variability between the grand minima and grand maxima (Steinhilber et al, 2010; Hathaway, 2015; Usoskin, 2017). The “extended” MM has been split into three phases by Vaquero & Trigo (2015): a “decay phase” (1618–1645), a “deep Minimum” phase (1645–1700) and a “recovery phase” (1700–1723) and we here investigate two total eclipses of the Sun during the recovery phase In this context, it has been discussed to what extent the Sun kept its magnetic structure during the MM in comparison with the normal cycle minima that have been detected since the end of the MM (e.g., Eddy, 1976; Cliver & Ling, 2011; Riley et al, 2015), partially on the basis of the coronal structure of the MM as an indicator. The solar corona during total eclipses at solar cycle maxima becomes radial with numerous streamers, whereas that at solar cycle minima has symmetric extension of streamers only around the solar equator, as illustrated by Figure 1
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