Although the run of strong to storm Leonid returns seen from 1998-2002 is unlikely to repeat again until the 2030s (or perhaps even till next century), independent model calculations by David Asher, Esko Lyytinen & Marku Nissinen, Mikhail Maslov and Jeremie Vaubaillon have indicated 2009 may bring strong rates again. Various possible maxima and Zenithal Hourly Rate (ZHR) strengths have been proposed, primarily due to dust trails left by the shower's parent comet 55P/Tempel-Tuttle at its 1466 and 1533 returns, with the better peaks expected between roughly 20:40 to 22:00 UT on November 17.
Esko & Marku have suggested the 1466 trail may produce ZHRs above 20 from about 06:30 UT on November 17 till 00:30 UT on November 18, with a denser dust region likely producing ZHRs above 40 from circa 16h-23h UT on the 17th. This denser 1466 region will probably combine with the 1533 trail to push ZHRs up perhaps towards 150 or higher at some stage between 21h-22h UT that day. A recently-published re-evaluation by these two analysts in the August issue of the International Meteor Organization's (IMO's) journal WGN has suggested the peak ZHR may be somewhere between 150 to 300, centred around 21:28 UT on November 17. Mikhail has suggested ZHRs should peak between 21h-22h UT then too, at ~130-140. Jeremie's modelling has been revised yet more recently, following the Earth's encounter with the 1466 dust trail in 2008. Unfortunately, this has led to the downgrading of what he originally thought could be storm-proportion rates to probably 'only' strong activity. The time such rates are anticipated has altered hardly at all in this fresh examination however, suggesting ZHR peaks on November 17 around 21:43 (1466 trail; ZHR ~115) and 21:50 UT (1533 trail; ZHR ~80). The proximity of these two encounters may mean combined rates of about 200 could occur briefly. The 1466 encounter may happen between 30 to 60 minutes later than this though.
Aside from these main events, other less active submaxima may occur as well, on November 17 around 07:27 (ZHR maybe ~25; the timing marginally adjusted, and the strength of this event also now greatly downgraded by Jeremie) and 09h UT (ZHR ~25-30), and on November 18, at about 00:04 (~15), 03:29 (1102 AD trail; low rates?) and 19h UT (~10-15, probably of faint meteors). The Earth passes closest to the node of the comet's orbit just after 15h UT on November 17, with a likely ZHR of ~10-20.
Clearly, the evening to early morning UT hours of November 17-18 will create most interest for watchers, but none of these predictions is guaranteed of course, nor can other unexpected peaks be ruled-out. Whatever takes place, new Moon on November 16 ensures perfect viewing conditions.
The Leonid radiant rises only by ~23h UT, and reaches a fully usable elevation after midnight from Britain. Consequently, we will likely miss the very best Leonid activity, if the predictions are accurate. However, watching from the UK will probably be most rewarding towards dawn on November 16-17, plus around and shortly after radiant-rise on November 17-18. Coverage at times when the radiant is readily-seen on these nights, and others, would be important as well, and could catch any unanticipated peaks. If the 1466 trail peak is an hour later than predicted, so around 22:45 UT on the 17th, and does produce rates of 100+, one or two Leonids might be seen near then from Britain, at or shortly before radiant-rise. Such meteors would be very long-pathed, so might seem to be moving slower than the usually very swift Leonids should do, while heading away from the radiant area as normal. Worth looking out for, just in case.
For more information and a Leonid radiant chart, see the November meteor activity webpage at:
http://www.popastro.com/sections/meteor ... ov2009.htm
Good luck, and clear skies!
Meteor Director, Society for Popular Astronomy.
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