55P/Tempel-Tuttle, the parent comet of the Leonid stream, returns to perihelion every 33 years or so (in fact very close to 3 times a century), generating a new trail of meteoroids and dust each time. Until they disperse after a few centuries into the Leonid stream as a whole, these narrow trails are regions that have a high density of meteoroids, and so there is a meteor storm if the Earth passes through a trail. A review article by David Asher entitled `Leonid dust trail theories' is available as paper number 346 in the Armagh preprint/reprint series.
Plots are available on these web pages for the following years:
Plots copyright David Asher, Armagh Observatory; may be reproduced for private or educational use.
This work has been done in collaboration with Robert H. McNaught, Research School of Astronomy and Astrophysics, Australian National University.
Description of plots
The Earth's path is shown in blue with the Earth's physical size enlarged 10 times. The place where the comet crossed the ecliptic is a green cross. Particles in the trails move pretty much in the opposite direction to the Earth, except that their path is inclined at about 17 degrees (moving downwards; plots being viewed from above), and so just the positions where the trails intersect the ecliptic are shown. These cross sections are labelled by the year in which the trail was generated. Generally, positions have been calculated for the 6 most recent trails, i.e., up to 200 years old. The 7, 8 and 9 revolution old trails have been added in 1999-2002. Trail cross sections can be absent when the relevant bit of the trail has already been perturbed or dispersed, so that there is no intersection with the ecliptic in mid-November of the year in question. The cross sections are drawn schematically as coloured ellipses. In reality, there is some density profile that falls away the further one is from the centre of the trail, and cross sections of different trails, and at different points along the same trail, are not identical. The different colours give the age of the trail, not the density, although younger trails have some tendency to have stretched out less and to be therefore denser. McNaught and Asher have developed a model to estimate Zenithal Hourly Rates of meteors during trail encounters. As Leonid meteors are generally observable in the second half of the night, the dates (given in Universal Time in the plots) when the Earth encounters various trails determine which parts of the world can experience the meteor storms or outbursts. As examples, when the fractional part of the date is roughly 0.1, 0.4 and 0.8, respectively Europe & Africa, the Americas, and
East Asia are favoured. For example, the visibility map for the 2006 outburst shows that this outburst, which peaks at around Nov 19.2, can be seen from regions at the west of Europe and the west of Africa, and from some eastern parts of the Americas. Note that the plots are only to illustrate encounters with young trails within the Leonid shower; overall, Leonid activity lasts, at a fairly low level, for several days.
Many of the Earth's encounters with Leonid trails were calculated by Kondrat'eva, Murav'eva and Reznikov, and further encounters were identified in the research of Esko Lyytinen (who has also found some very interesting results on the Perseids). The determinations of encounter times are independently confirmed by Kondrat'eva et al., Lyytinen, and McNaught & Asher, and are also consistent with the work of Brown & Jones, who have constructed an extensive physical model of the whole Leonid stream.
Last Revised: 2009 November 10th