|Discovered by||Johann Georg Tralles|
|Discovery date||July 1, 1819|
Great Comet of 1819
|Orbital characteristics A|
|Last perihelion||June 28, 1819|
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.
On July 1, 1819, Johann Georg Tralles in Berlin observed a brilliant comet low in the sky during the evening twilight. It was confirmed the next night by the astronomer Johann Elert Bode, also in Berlin.
On July 2, Tralles found the comet to have a coma of 40″. On July 3, Friedrich Georg Wilhelm von Struve measured the nucleus at 8″ with a tail of several degrees. Heinrich Wilhelm Matthias Olbers reported that the nucleus had an apparent magnitude of 1–2 and a tail about 7–8° long. The comet was last sighted by Struve on October 25.
Also on July 3, François Arago used a polarimeter of his own invention to analyze the light from the comet's tail and discovered that it was polarized. He then observed the nearest star, Capella, which did not show polarized light. This indicated that some light from the comet's tail was reflected from the sun. This marked the first polarimetric observation of a comet.
After the orbital elements of the comet were calculated by Olbers, he discovered that a transit of the Sun by the comet had occurred on June 26, days before its first observations. He reported this to Bode on July 27.
Orbital elements for the comet were calculated by several astronomers. The orbit is classified as parabolic and is nearly perpendicular to Earth's orbital plane, with an inclination of 80°. It passed closest to the Earth on June 25 at a distance of 0.67 AU (100,000,000 km; 62,000,000 mi) and closest to the Sun on June 28 at 0.34 AU (51,000,000 km; 32,000,000 mi).
In 2016, the orbit was recalculated based observations of the comet taken in 1819.
The comet was widely seen and noted by people who were not astronomers. Poet John Keats noted how he and his wife Fanny had stared at the comet. Historian Nathaniel Philbrick writes about the great comet seen in July 1819 by the people on the island of Nantucket, Massachusetts in his 2000 book, In the Heart of the Sea.
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