[ChessExpert]

The variation in sunspot numbers has revealed the Sun's 11-year cycle of activity

Would those be 11 earth years? Jupiter years? Mars years? Is that 11.000 years? Does this 11.000 year sun cycle have a standard deviation of 0.000?

I suspect we can compute an average (in earth years). It is not 11.000. I think I read 11.29 someplace. But if you collect a different sample of years, you will get a different mean. And who says the mean is the best measure? Maybe we should use the median or mode? The standard deviation is not zero. So let’s acknowledge it. Maybe a proper formulation would sound like this: The solar cycle is 11.295 years plus or minus 2, based upon data from 1006 to 2006. The number of sunspots vary with each cycle.

[Robert A Cook PE]

A “year” (in terms of time measurement for science) is always an “earth-year” and “earth-second when shorter intervals need to be measured) - and for this article, I agree with you that the precise 11.29 interval is rounded out.

Accurate enough.

What was not immediately clear is how the author extrapolated back from direct measurements to get the nbr of sunspots before Galileo started watching the sun itself. Since the 1600’s, we can count them (have counted them) but before then ...