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Leonid Predictions 1999
Coming Perseid Meteor Storms

AUTHOR: Esko Lyytinen
E-mail: Esko.Lyytinen@MINEDU.FI

The orbit of comet P/Swift-Tuttle has been passing outside the Earth's orbit at least for the last 2000 years. The last return in 1992 was an exception. Already during the previous return in 1862, the perihelion distance might have had a lower value than during any of the previous history that can be reliably calculated.

Four revolutions back, the perihelion distance was almost as low as in 1862.   It is doubtful that the Earth has ever encountered a fresh meteor trail from this comet. In 2004, the one-revolution trail from 1862 will pass inside the Earth's orbit. At the time of Perseids (the annual meteor shower associated with this comet), the rE-rD has a value of about +0.0012 au. Earth passes the trail node at solar longitude (2000.0) 139.441°. This occurs at 11 August 20:54 UT. If there were a closer approach, a real meteor storm would be expected. But with these conditions and no prior storms to judge by, it is uncertain what kind of a shower this will give.

The Moon will be a relatively narrow waning crescent in 2004, with Europe and Western Asia in the most favorable viewing locations. The principles I use in my unpublished Leonid ZHR-model would give zenith hourly rates about 100 from this trail, if the numbers of particles released were the same as for Leonid-parent-comet Tempel-Tuttle. But since the Perseid parent comet is a lot bigger than the Leonid comet, there may be a chance of storm level activity. Because the planet Jupiter lowers the ecliptic crossing radii in general this year (2004), there may be enhanced general activity as well.

The one-revolution trail may give a short shower with a half-strength duration of only about fifteen minutes. In the year 2028, the Earth will pass within about -0.0004 au (rE-rD) of the 4-revolution trail from the year 1479, with a mean anomaly factor of about 0.15. I expect this to produce a real storm over the U.S., although under unfavorable moonlight conditions.

Figure 1

Figure 1. The ecliptic crossing of 1-to-4-revolution meteor trails left by comet Swift-Tuttle. In the calculations, the original particle density is the same for 1-to-3-rev. trails. For the 4-rev. trail, the density is four times bigger. For the 1 rev. trail, the number of visible meteors is expected to start to decline more than about 10 years behind the comet. So prospects for a good shower from the 1-revolution trail are clearly best in 2004. In each figure, the vertical line is the start of the year. Similarly, the line at the location 2005 extending a bit downward from the others (for example) denotes the start of the year 2005. Visible Perseids meteors occur at about 0.61 of the way through each year.

Figure 2

Figure 2. The 1-revolution trail at a different scale in 2004. The year is divided into 12 months.

Figure 3

Figure 3. The 4-revolution trail plotted after the year 2020. The trail is getting irregular, but the number of visible meteors within the trail is expected to be dense enough in 2028 to give storm-level activity. This shower/storm is expected on 12 August at about 05:30 UT.

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