Comet of the Week: 3D/Biela 1846 II

Ice and Stone 2020: Week 08 Content

The two components of Comet Biela on February 19, 1846 as sketched by Otto Wilhelm von Struve at Pulkovo Observatory near St. Petersburg, Russia.

Comet 3D/Biela 1846 II’s Perihelion: 1846 February 11.49, q = 0.856 AU 

The stories of the first two numbered periodic comets, 1P/Halley and 2P/Encke – both of which are future “Comets of the Week” – are well known. The third numbered periodic comet also has an interesting story, but unlike the earlier two, it will likely never be seen again, at least, in “cometary” form. 

The comet was first discovered on March 8, 1772 by the French astronomer and comet hunter Jacques Montaigne, a contemporary and competitor of Charles Messier (who himself independently spotted it shortly thereafter). It remained just below naked-eye visibility (i.e., around 7th magnitude) and was followed for slightly under one month. Five returns later the French comet hunter Jean Louis Pons discovered it on November 10, 1805; on December 9 of that year, it passed just 0.037 AU from Earth and was easily seen with the unaided eye at 4th magnitude or brighter. Some of the mathematical astronomers of that era, among them Carl Gauss, noticed a similarity between the 1806 comet and the 1772 comet but could not establish an identity between them. 

An Austrian army officer, Wilhelm von Biela, discovered a comet on February 27, 1826; as he was also skilled at computing orbits he soon determined it was likely that this comet was the same as the comets that had appeared in 1772 and 1806. It was followed for long enough that year such that the link between them could be firmly established, and the orbital period was determined as being 6.7 years. 

The comet returned as expected in 1832 but was missed at the unfavorable return in 1839. At the following return the then-Director of the Vatican Observatory, Francesco de Vico, recovered it on November 26, 1845. Initially, there didn’t seem to be anything unusual about it, but starting in mid-January 1846 a “companion” comet was found to be accompanying the main one. This “companion” remained visible until the end of March with the primary comet subsequently being followed for another month. The following return, in 1852, was not an especially favorable one, but once again the “companion” comet appeared alongside the primary one during most of the one-month-long interval that they were visible. 

The next return, in 1859, was very unfavorable and the comet was not recovered. The viewing geometry at the return after that, in 1866, was very favorable, however, with the comet’s being expected to pass 0.22 AU from Earth in late February, but despite several careful searches the astronomers of that era found . . . nothing. The comet likewise failed to show up at the subsequent return in 1872, however on November 27 of that year an intense meteor shower – with rates up to 10,000 meteors per hour was seen coming from the general area of the constellation Andromeda. Similar strong “Andromedid” showers appeared in 1885 – during which the first successful photograph of a meteor was taken, by Hungarian astronomer Ladislaus Weinek – and in 1892, and a weaker shower appeared in 1899. All of these were around the time that Comet Biela would have been passing through perihelion, and although the Andromedid shower itself had been known since 1741, the shower’s strong displays those years combined with the comet’s splitting and then failure to appear have been construed as evidence that the comet completely disintegrated not too long after the middle of the 19th Century. 

A representation of the Andromedid meteor shower over France on November 27, 1872, as presented by French science journalist Amedee Guillemin.

There have nevertheless been some attempts to recover Comet Biela in the years since then. One of the strongest efforts took place in 1971, when Brian Marsden calculated that if some asteroidal fragment remained and if it had ceased activity around 1859, it would be passing close to Earth late that year. Despite several searches, no trace of Biela was found then, nor at any other time. For what it’s worth, in 2001 the NEAT survey program discovered a faint periodic comet that travels in an orbit quite similar to that of Biela, but is apparently an unrelated object; now known as Comet 207P/NEAT, it will pass 0.22 AU from Earth in March 2024. 

The lack of any strong Andromedid activity after 1899 has often been taken as a sign that Comet Biela has all but completely dispersed, however meteor expert Peter Jenniskens has pointed out that the dust stream that produces the Andromedid shower has likely shifted away from Earth due to gravitational perturbations from the planets, and in fact there does appear to be some very weak Andromedid activity from time to time. On December 5, 2011, a moderately strong Andromedid shower, with a peak rate of some 50 meteors per hour, was seen from Canada. A shower with similar rates that was expected to occur in 2018 apparently did not take place, but a possible Andromedid shower with potential rates as high as 200 meteors per hour may occur in 2023. The entire art of predicting meteor showers has developed dramatically during the past couple of decades, and the linkage between comets and meteor showers is the subject of a future “Special Topics” presentation. 

Meanwhile, there seems to be a modern-day equivalent, of sorts, to Comet Biela. Comet 141P/Machholz 2 abruptly brightened to 7th magnitude and was accompanied by up to four “companion” comets (two of which were fairly bright) during its discovery return in 1994. One of these “companion” comets returned with the primary component in 1999, although it soon faded out. The comet was poorly placed for observation in 2005 and 2010, but was well placed in 2015; it was significantly fainter (12th magnitude) than it had been previously but was again accompanied by a fainter “companion” comet. It passes perihelion again late this year, under favorable viewing conditions (with its passing 0.52 AU from Earth in mid-January 2021) and . . . we’ll see what happens. 

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