Jeremy. In reviewing the 4 definitely observed eruptions, Brad Schaefer’s comments that the recurrence timescales are 7×81.4, 78.5, 79.7, and then states a likely 78.3 ± 0.3 yr should apply between 1946 and the next eruption. So that translates to 2024.4 ± 0.3. I don’t understand how he can ascribe such a small uncertainty (± 0.3 yr) in this prediction. Statistically from the above numbers you could envisage a distribution in which 9 eruptions span the range 77 to 85 yr, and that since the last two have been in the lower half of that distribution, the next event has more chance of being in the higher half, i.e. more like 82 ± 3 yr, which then takes it to the beginning of 2026. It does look like he has made an assumption that the periodicity is for some reason decreasing on average monotonically in a somewhat linear fashion. Is there some theoretical reason why that might be the case, I wonder?
P.S. Brad Schaefer has done all sorts of research over the years. Am putting together a paper at present that uses three references to his work from 1985, 1986 and 1987. He writes that he was the first to work on this subject since antiquity and few if any other visual observers have since investigated this topic. The references are:
Schaefer, B.E., 1985. “Predicting heliacal risings and settings”, Sky and Telescope, lxx, 261–3.
Schaefer B. E., 1986, “Atmospheric extinction effects on stellar alignments”, Archaeoastronomy (Supplement to Journal for the History of Astronomy), (10), S32–42.
Schaefer, B.E., 1987. Heliacal rise phenomena. J. Hist. Astron., 18(11), S19.