Solar Terrestrial Activity Report
Overview of solar and geomagnetic activity. Graphical comparison of recent solar cycles, sunspots, and solar flux. Generally updated once a day.
www.dxlc.com/solar
Galileo Project: Sunspots
Records of their occurrence from the 1600s.
es.rice.edu/ES/humsoc/Galileo/Things/sunspots.html
Inter-Sol Programme (ISP)
International programme with the purpose of observing the daily sunspot activity.
www.Inter-Sol.org
Sunspot Numbers
Introduction to how they were first computed by Rudolph Wolf in 1848, and how they are computed today.
web.ngdc.noaa.gov/stp/SOLAR/SSN/ssn.html
Exploratorium's Guide to Sunspots
Explore the nature of sunspots and the fascinating history of our efforts to understand them.
www.exploratorium.edu/sunspots