Hokey Data In The Maunder Minimum

The stunning lack of sunspots from 1645 to 1715 (Maunder Minimum) and the cool years associated have to be addressed when you talk about the sun and climate change.  Willis Eschenbach  writing at WattsUpWithThat was busy checking into something else (possible links between volcanos and sunspots) when he discovered unseemly holes in the original sun spot diaries.

Johann Zahn

This is the Zahn's data for the year 1632 in Germany.  The -99 number means there were five days that year when no observations were taken.  All the other entries are zero which means that there were 360 un-cloudy days in Germany that year and no spots were seen in all 360.  Eschenbach writes that most of the years just prior to the Maunder Minimum appear to have about two thirds of the data missing.   Bizarrely, during the Minimum, the opposite is the case with only 3% of the data missing.

No one is saying there was no Maunder Minimum but it looks to have been overstated.   The original entries by Herr Zahn may have conflated days with no sunspots and days when no observations were attempted.  There's a lot more detail at the site with links to sources.