*Chris Plicht "Schwabe, Samuel Heinrich (1789 - 1875)" [http://www.plicht.de/chris/32schwab.htm]*The Sun—History [http://www-istp.gsfc.nasa.gov/Education/whsun.html]
* Chris Plicht «Schwabe, Samuel Heinrich (1789—1875)» [http://www.plicht.de/chris/32schwab.htm]* The Sun—History [http://www-istp.gsfc.nasa.gov/Education/whsun.html]