Ursids

The Ursids are a meteor stream, which is observable in the last decade of December. The parent body of this meteor stream is the comet 8P/Tuttle. His Radiant is located in the constellation Ursa Minor at Kochab. The radian is therefore circumpolar. The Ursids have a ZHR of 10 meteors per hour. However, significantly higher numbers were observed sporadically.

History

The Ursids were discovered in 1900 by William F. Denning, but learned a long time little attention. On December 22, 1945 Czech astronomers observed by chance a strong outbreak of the meteor shower, with a ZHR of about 100 was reached. In the following years the Ursids were systematically investigated, the observed meteor numbers were compared with 1945 but always very low. Therefore, the interest in this meteor shower was soon after again. Only in the early 70s made ​​further investigation by British amateur astronomer, with very low ZHR were found. However, a short burst with a ZHR of about 30 was detected in the daylight hours of December 22, 1973 by radio observations. Comparable strong were the Ursids on 22 December 1979 in appearance, this time it was Norwegian observers could view the meteors in the night sky. In several European countries a much stronger burst of Ursids, with ZHR was observed up to 100 on 22 December 1986.

It has long been known that it is the origin of comets Ursids at 8P/Tuttle. The orbital period of this tail star is 13.5 years. Interestingly, the observed outbreaks of Ursids fell in the years 1945, 1973 and 1986, not with the sun nearby, but with the aphelion of the comet together. Peter Jenniskens and Esko Lyytinen developed a model that this unusual phenomenon among others explained by the gravity of Jupiter. The same authors said on 22 December 2000 - again, the comet was in aphelion - a new outbreak of Ursids before. Many observers lay in wait, but the results were contradictory. First of all video recordings and radio echoes pointed to increased meteor activity, but there were doubts about the methodology applied here. In addition to that visual observers recorded only the usual low Ursids rates.