The Meteor Storms of November – Part I – The Andromedids
November 15, 2008
Meteor showers are called “showers” for a good reason. The steady fall of meteors resembles the steady fall of raindrops in a rain shower. But similar to rain, there are times when a large number of meteors are seen and we experience a “storm”. More akin to thunderstorms, meteor storms produce very short (10-60 minute) “downpours”.
The month of November is witness to three different meteor showers that have caused major meteor storms in the past. Most years these showers are minor and produce rates much lower than last month’s Orionids. But a few times per century, the skies have opened and a storm has occurred. This post will focus on the first of the three storm producing showers, the Andromedids, or the Bielids, as they are sometimes called. This year the Andromedids have already passed. The reason why I made no mention of it before is because this shower has become a very minor shower. In fact, visual observers have had a hard time detecting it over the past century. Only in video meteor camera data has a hint of activity been detected.
The Rise, (Split) and Fall of Comet Biela
The story of the Andromedids starts with the discovery of Comet Biela, or to be more exact, the many discoveries of Comet Biela. Similar to the discovery story of Comet Encke in the Taurid Preview post, Comet Biela was found a few times before astronomers recognized it as the same comet. The first person to see the comet was Jacques Leibax Montaigne of Limoges, France, who found it on 1772 March 8. Since the comet was observed for less than a month, an accurate orbit could not be computed and the comet’s periodic nature was not recognized.
The comet was re-discovered on 1805 November 10 by J. L. Pons. During this return the comet passed very close to the Earth (0.037 AU). Enough observations were made that a reasonable orbit was calculated and some astronomers noticed the similarity between the orbits of this comet and Montaigne’s comet of 1772. But the link wasn’t definite and it would take another re-discovery to make a perfect link.
The 3rd discovery happened on 1826 February 27 when Wilhelm von Biela of Josephstadt, Austria, found a faint comet in the constellation of Pisces. Biela and other astronomers quickly noted that this comet was one and the same with Pons’ 1805 comet and Montaigne’s 1772 comet. With a period of ~6.6 years the comet was observed again in 1832. After being missed during the unfavorable return of 1839, the comet was recovered in 1845 which is when the story gets really interesting.
For a month and a half after recovery, the comet showed no sign of anything unusual. Then in mid-January of 1846, observers found a companion comet traveling along side Comet Biela. [See the post on Comet Giacobini for a recent example of a split comet.] The two comet components slowly separated over the next few months.
When the comet returned in 1852, the two pieces of Comet Biela were observed once again. Due to poor observing circumstances in 1859, the comets were next expected to be seen in 1866. But the comets were never seen again and their whereabouts, or even if they still exist or not, is unknown. [A comet discovered by the NEAT asteroid survey in 2001 may be a piece of Comet Biela. Whether Comet 207P/NEAT is related to Comet Biela is still conjecture.]
The Rise and Fall of the Andromedid Meteor Shower
On the night of 1741 December 6, a large number of meteors were noted over the city of St. Petersburg, Russia and marks the first sighting of the Andromedid meteor shower. Additional strong outbursts were seen in 1798, 1825, 1830, 1838 and 1847. None of them compared to the showing the Andromedids would make in 1872.
By 1872, the story of Comet Biela had unfolded. Also by this time, the link between comets and meteor showers was well established. Some astronomers, such as Edmond Weiss whose book included the drawing shown in the last section, predicted that the Andromedids would be observable on 1872 November 27-28. And what a meteor display that was. Modern research into the 1872 storm suggest that rates reached as high as ~7000 meteors per hour, or roughly 2 meteors per second.
Thirteen years later, another major storm was observed on 1885 November 27 when ~6000 meteors per hour were observed. At the time, astronomers thought the large number of meteors were due to the complete break-up of Comet Biela. It was suggested that the Earth must have traveled through the debris left over from the comet’s demise. But work reported by Peter Jenniskens in his excellent book on meteor showers, “Meteor Showers and Their Parent Comets“, suggests that the 1872 and 1885 storms were due to the Earth crossing the dust trails left behind by Comet Biela in 1846 and 1852. Based on the number of meteors observed, he finds that the meteor storms could be accounted for by a normal level of cometary activity. This suggests that Comet Biela did not release a large amount of dust when it broke into two. This means that even if Comet Biela not split, the Andromedids would still have stormed.
Though much smaller outbursts were observed in the years after the 1885 storm, the shower was nearly impossible to observe by the early 20th century. What happened? The Andromedid meteor shower is still out in space but its orbit has shifted an no longer intersects the orbit of the Earth. As a result, no additional Andromedid storms are possible. At least not for a few centuries when the orbit will once again be in the vicinity of Earth.
Analysis of meteors detected by video camera over the past few years found evidence of very low level Andromedid activity. The meteors were observable between November 1 and 19 with a peak on November 5. Though even at their peak, these residual Andromedids accounted for less than 1% of all the meteors observable that night. As a result, this meteor shower is more of a historical curiosity than something that modern observers can experience.
Next on our tour of November meteor storms, the Leonids…