Comet Donati

Lore & Background

Donati first observed the comet on 2 June from the Florence Observatory, initially as a small nebula-like object of magnitude 7 near the 'head' of Leo. By mid-August it had brightened sufficiently to be visible to the naked eye. In September it passed into Ursa Major, and for much of its apparition it occupied a unique position among great comets in the sky, particularly well placed for Northern Hemisphere viewers. It was nearest Earth on October 10, 1858, and for much of October was a brilliant object with a long, scimitar-like dust tail and prominent gas tail. It remained a naked-eye object until November for Southern Hemisphere observers. The final observation was by William Mann, chief assistant at the Royal Observatory, Cape of Good Hope, who detected it as a faint nebulosity on March 4, 1859.

The comet was successfully photographed on September 27 by W. Usherwood, a portrait photographer at Walton-on-the-Hill, Surrey, using a 7-second exposure with an f/2.4 portrait lens, the first time a comet had been photographed. Usherwood's photograph, now in archival storage at Harvard College Observatory’s Astronomical Photographic Glass Plate Collection, showed the bright region around the comet's nucleus and a part of the tail. G. P. Bond also successfully photographed the comet on September 28 at Harvard College Observatory, the first comet photograph through a telescope. He made several attempts with increasing exposure times, finally achieving a discernible image, writing that 'only the nucleus and a little nebulosity 15" in diameter acted on the plate in an exposure of six minutes'.

Orbits for the comet were calculated by Friedrich Emil von Asten and George William Hill, the latter's based on nearly 1000 positions. The comet had an orbital inclination of 116.9°. With an epoch 2200 barycentric orbital period approximated at 1739 years, it is estimated that Donati's Comet will not be seen passing by Earth again until somewhere around the year 3600. As of 2023, JPL Horizons estimates that the comet is 147 AU from the Sun and continuing to move away at 2.4 km/s. The comet's orbit lies very close to that of Venus, with the minimum intersection distance being 0.0047 astronomical units (700,000 km; 440,000 mi), the smallest known distance a great comet can approach a terrestrial planet. It is possible the comet produces a strong meteor shower at the northern hemisphere.

Reader's Guide

Donati's Comet is considered one of the most beautiful comets observed and was one of the brightest of the century, making a strong impression both on artists and the general public. After a prior period of hysteria on the subject of comets, especially in Paris (caused partly by incorrect calculations by John Russell Hind which suggested that one would strike the Earth in June 1857), Donati's Comet went on to be the most-observed of the century due to its excellent visibility in dark skies for Northern Hemisphere viewers, particularly in Europe, and fine weather in September and October. William Henry Smyth recalled it as 'one of the most beautiful objects that I have ever seen'. Donati himself, a relatively obscure figure, was propelled to the status of an astronomical hero, and the comet helped cultivate a general enthusiasm for astronomy among the public.

The comet appears as a streak and star in the early evening sky of a painting by William Dyce, Pegwell Bay, Kent – a Recollection of October 5th 1858. It was featured in a number of sketches and at least one painting by William Turner of Oxford, and in a painting, 'The Comet of 1858, as seen from the Heights of Dartmoor', by Samuel Palmer. The Comet at Yell'ham, a 1902 poem by Thomas Hardy, was inspired by his recollections of Donati's Comet. Abraham Lincoln, then a candidate for a seat in the U.S. Senate, sat up on the porch of his hotel in Jonesboro, Illinois, to see 'Donti's Comet' on September 14, 1858, the night before the third of his historic debates with Stephen Douglas. Naturalist Alfred Russel Wallace wrote of seeing the comet in October 1858 off the island of Tidore in Indonesia, describing its brilliant white nucleus and sharply defined upper tail margin. The influence of the comet, particularly in visual and design terms, was such that traces of its appearance can be found in magazine and commercial illustrations, household objects, children's books and other items up until the early years of the 20th century.

Did You Know?

• Donati's Comet was the first comet ever photographed, captured by W. Usherwood on September 27, 1858.
• Abraham Lincoln observed the comet on September 14, 1858, the night before his third debate with Stephen Douglas.
• The comet's orbit has the smallest known approach distance to a terrestrial planet (Venus) at 0.0047 AU.
• Naturalist Alfred Russel Wallace saw the comet from the Malay Archipelago in October 1858.