The time series of the #sunspot number — long used as a proxy for solar activity — covers more than 400 years of observations.

However, earlier data suffer from temporal gaps and variable quality. These issues are taken into account in the creation of a way to visualize long-term #solar variability.

This is probsbly the longest running observational project conducted by modern scientists.

#astronomy #sun #astrophotography
https://www.nature.com/natastron/volumes/3/issues/3