Biela's Comet

The comet was first recorded on 8 March 1772 by Jacques Leibax Montaigne; During the same apparition, it was independently discovered by Charles Messier. The comet was also recorded in 1805 by Jean-Louis Pons, but was not recognized as the same object at the time.

Observational history

Discovery

Around 9 December 1805, Comet Biela passed about 0.0366 AU (5.48 million km) from Earth. After the 1805 apparition a number of attempts were made by Gauss (1806) and Bessel (1806) to calculate a definitive orbit. Gauss and Olbers both noted a similarity between the 1805 and 1772 comets but they were not able to prove a link.

Confirmation as periodic

It was Wilhelm von Biela, an army officer serving at the fortress town of Josefstadt, who observed the comet during its 1826 perihelion approach (on February 27) and calculated its orbit, discovering it to be periodic with a period of 6.6 years. At the time it was only the third comet known to be periodic, after comets 1P/Halley and 2P/Encke. The comet was named after Biela, although there was initially some controversy due to a later but independent discovery by Jean-Félix Adolphe Gambart, who also provided the first mathematical proof linking the 1826 and 1805 comets (letters from Biela and Gambart were published in the same issue of the Astronomische Nachrichten). A third claim was made by Thomas Clausen, who had independently linked the comets.

Olbers in 1828 predicted that in 2500 years, a collision with earth was probable. This became the framing story of The Year 4338: Petersburg Letters.

The comet appeared as predicted during its 1832 apparition, when it was first recovered by John Herschel on 24 September. The orbital elements and ephemeris calculated by Olbers for this return, and updated by Marie-Charles Damoiseau to take into account the gravitational effects of the planets, created something of a popular sensation, as they showed that the comet's coma would likely pass through the Earth's orbit around October 29, but at an Earth distance of about 0.55 AU (82 million km). Subsequent predictions, in the media of the time, of the Earth's likely destruction overlooked the fact that the Earth itself would not reach this point until November 30, a month later, as pointed out by François Arago in an article designed to allay public fears. He put the probability of collision to 1/281 million, though admitted that the comet tail gases may cause "the death of all animals, or produce epidemics".

Despite this, the fact that Biela's Comet was the only comet known to intersect the Earth's orbit was to make it of particular interest, both to astronomers and the public, during the 19th century. In 1832, Greek-Austrian astronomer Georgios Konstantinos Vouris published his own calculations of the elliptical orbit of the comet entitled: Elliptical orbit calculation of Biela's Comet from 96 observations of the year 1832 (Elliptische bahnbere chung des Biela'schen cometen aus 96 beobachtungen des Jahres 1832). His article was a comprehensive overview of the elliptical orbit of Biela's Comet.

The 1839 apparition was extremely unfavourable and no observations were made as the comet never came closer than 1.8 AU from Earth since the comet was on the other side of the Sun. During 1839 the comet never had a solar elongation greater than 50 degrees. Despite its disintegration, Rudolf Falb predicted in 1899 that it would collide with earth on 1899-11-13, destroying it. The prediction "caused no little dismay among the poorer classes of the Continental peasantry".

Biela and Lexell's Comet may have inspired Edgar Allan Poe's The Conversation of Eiros and Charmion (1839).

Disintegration

As of 1832, Comet Biela had an Earth-MOID (Minimum orbit intersection distance) of only 0.0005 AU (75,000 km). The comet was rediscovered on 26 November 1845, by Francesco de Vico. Initially sporting small, faint nebulosities, subsequent observations showed that something remarkable had happened to it. Matthew Fontaine Maury, observing on 14 January 1846, noted that an apparent companion was located 1 arc minute north of the comet. After this announcement many astronomers began observing the comet, and noted that the two elements (usually referred to as "Comet A" and "Comet B" in modern nomenclature) alternated in brightness, developing parallel tails as they approached perihelion. Some observations indicated an "archway of cometary matter" extending between the two nuclei, which might suggest that the comet had split into many more pieces than two, but the smaller pieces were simply too faint to be observed individually.

In 1852, the comet was again rediscovered more or less as predicted, with "Comet A" being rediscovered first, by Angelo Secchi on August 26. "Comet B" was finally relocated on September 16, and once again both nuclei alternated in brightness during the period of observation. "A" was last detected on this apparition on September 26 and "B" on September 29, in both cases by Otto Wilhelm Struve. Subsequent orbital calculations indicated that the nuclei had probably split around 500 days before the 1845 apparition, though more recent work has determined that it may have occurred near aphelion in late 1842.

Neither part could be found on their predicted periodic returns in 1859 (in any case an unfavorable return for viewing), 1865, or 1872. However, on 27 November 1872, a brilliant meteor shower (3,000 per hour) was observed radiating from the part of the sky where the comet had been predicted to cross in September 1872. This was the date when Earth intersected the 1839 and 1846 meteoroid streams. These meteors became known as the Andromedids or "Bielids" and it seems apparent that they were produced by the breakup of the comet. The meteors were seen again on subsequent occasions for the rest of the 19th century, but have now faded away, due to gravitational perturbations moving the node outside of Earth's orbit.