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132 WGN, the Journal of the IMO 30:5 (2002) The Leonids

Summary: 132 WGN, the Journal of the IMO 30:5 (2002)
The Leonids
Leonid Dust Trail Structure and Predictions for 2002
Robert H. McNaught and David J. Asher
We discuss the in uence of non-linearities in dust trail dynamics caused by the passage of the Earth close to or
through dust trails. The e ect is to make the derived parameters of these non-linear dust trail sections unreliable
for prediction or for use in tting observed data. These non-linearities become more common in dust trails as
they age, but linear sections remain. The timing of encounters with linear sections of dust trails is con rmed as
being within 10 minutes and typically 5 minutes. A qualitative examination of incipient dust trails show that
they have a pro le that is skewed away from the Sun, that the dust trail pro le is a function of a 0 and that
trails have a dense core at formation which will di use out over a few revolutions. Despite this, the density model
now gives a reasonable t over the region of parameter space responsible for storms. There is evidence that the
peak region in our model for young trails may be underpredicted due to the existence of this enhanced core. A
new model to predict the FWHM of linear dust trail sections is given. The predictions for the two major peaks
in 2002 are: (i) 7-rev trail, 2002 November 19, 03:56  5 min UT, ZHR 1000 (810{2000), FWHM  130 min; (ii)
4-rev trail November 19, 10:34  5 min UT, ZHR 6000 (2900{6000), FWHM 71 min. The 7-rev encounter will
have a lower population index than the 4-rev.
1. Introduction
The technique for calculating dust trails from comets has been around for some fty years,
during which time it has been rediscovered on several occasions. Mostly it has been overlooked.


Source: Armagh Observatory


Collections: Physics