Johann Georg Tralles discovers the Great Comet of 1819, (C/1819 N1). It is the first comet analyzed using polarimetry, by François Arago.

Johann Georg Tralles was a German mathematician and physicist.

The Great Comet of 1819, officially designated as C/1819 N1, also known as Comet Tralles, was an exceptionally bright and easily visible comet, approaching an apparent magnitude of 1–2, discovered July 1, 1819 by the German astronomer Johann Georg Tralles in Berlin. It was the first comet analyzed using polarimetry, by French mathematician François Arago.

Polarimetry is the measurement and interpretation of the polarization of transverse waves, most notably electromagnetic waves, such as radio or light waves. Typically polarimetry is done on electromagnetic waves that have traveled through or have been reflected, refracted or diffracted by some material in order to characterize that object.

Dominique François Jean Arago, known simply as François Arago, was a French mathematician, physicist, astronomer, freemason, supporter of the Carbonari revolutionaries and politician.