Carrington's 1870 sunspot drawing yields a Wolf number of 40 and three group positions, computed by Hayakawa and Teague (2026)

astronomysolar-physicshistory-of-sciencecarringtonsunspot-numbermeasurement

Working from the newly located drawing described in claim-hayakawa-teague-2026-found-carringtons-unpublished-1870-sunspot-drawing, Hayakawa and Teague counted 3 sunspot groups and 10 individual spots and applied the standard Wolf-number formula, R = 10G + F (per Rudolf Wolf's own definition, as used in modern sunspot-number recalibration work), giving a relative sunspot number of 40 for 23 Dec 1870. They further derive heliographic group positions — N14° W37°, N11° W46°, and S08° W08°, with longitude measured as angular distance from the central meridian rather than Carrington longitude — using NASA JPL ephemeris data and a geometric deprojection of the drawing, with a stated uncertainty of roughly ±3°.

The authors use this single data point as part of a broader methodological argument: that Carrington's drawing shows a visibly lower group count than contemporaneous observers recorded on the same day, which they cite as a caution against the "Schmidt backbone" assumption in modern sunspot-number recalibration — that an individual historical observer's detection threshold stays constant across their observing career (see Schmidt backbone). That methodological argument is the authors' own interpretive layer on top of the measurement and is not independently tested against other backbone observers in this paper.