The Great Comet of 1811 was thought to have had an exceptionally large coma, perhaps reaching over 1 million miles across—fifty percent larger than the Sun. The comet's nucleus was later estimated at 30–40 km in diameter. Before perihelion passage on September 12, 1811, the comet had an orbital period of 2742 years. After perihelion passage the comet has a period of 2974 years. In many ways the comet was quite similar to Comet Hale–Bopp: it became spectacular without passing particularly close to either the Earth or the Sun, but had an extremely large and active nucleus.