Solar Data

• Greenwich Sunspot Group Reports
  1874 to 1981
• Mount Wilson Sunspot Group Reports
  1962 to 1999
• USAF observatory (and Mt.Wilson) Sunspot Group Reports
  1981 - 1999
• Royal Observatory Greenwich Photo Heliographic Results
  1874 - 1976
• Solar Images on glass and print 1903 - 1942: Online catalogue