Leonids (LEO)
Active: November 10-21
Maximum: November 17 15h10m UT
(nodal crossing at λo = 235°27) but see below
ZHR = 100+?
Radiant: α = 152° δ = +22°
Radiant drift: see Table 6
v∞ = 71 km/s; r = 2.9
TFC: α = 140° δ = +35° and α = 129° δ = +06° (β > 35° N) or
α = 156° δ = -03° and α = 129° δ = +06° (β < 35° N)
IFC: α = 120° δ = +40° before 0h local time (β > 40° N);\p
α = 120° δ = +20° before 4h local time and α = 160° δ = 00° after 4h (β > 0° N)
α = 120° δ = +10° before 0h local time and α = 160° δ = -10° (β < 0° N)
The most recent perihelion passage of the Leonids' parent comet, 55P/Tempel-Tuttle, in 1998 may be more than a decade ago now, but the shower's activity has continued to be fascinatingly variable from year to year. This year may produce another enhanced return, with ZHRs predicted to peak at 100+ according to independent theoretical work by David Asher, Esko Lyytinen & Marku Nissinen, Mikhail Maslov, and Jérémie Vaubaillon. Trails laid down by the comet in 1466 and 1533 are expected to be the chief contributors to whatever happens, with peaks on November 17, due at sometime from about 20h40m to 22h UT then. Esko & Marku's work suggests the 1466 trail may produce heightened rates generally, with ZHRs above 20, from about 6h30m UT on November 17 till 0h30m UT on November 18, and likely above ~ 40 from ~ 16h-23h UT on November 17. This increased ZHR level will probably combine with that from the 1533 trail to push ZHRs up perhaps towards 120 at some stage between 21h-22h UT on the 17th. Mikhail suggested ZHRs should peak in that hour too, with ZHRs of ~ 130-140, but Jérémie's modelling implied the chance of a possible meteor storm, with ZHR peaks around 21h44m (ZHRs ~ 950+) and 21h51m UT (~ 600) combining to give a rate perhaps in the 1000-1500 range briefly. Other submaxima with lower rates are possible too, around November 17, 7h26m (ZHRs ~ 200+), 9h (~ 25-30), November 18, 0h04m (~ 15) and 19h UT (~ 10-15, faint meteors), according to some of these same researchers. The nodal crossing time listed above is another possible peak, based on previous non-enhanced returns, though its ZHR is likely to be a more modest 10-20.
Clearly, the evening to early morning UT hours of November 17/18 are likely to be of greatest observer interest. Luckily, new Moon on November 16 ensures perfectly dark skies for covering whatever events happen (remembering that there are no guarantees in meteor work!). As the Leonid radiant rises usefully only around local midnight (or indeed afterwards south of the equator), the 21h-22h UT apparently critical interval will fall best chiefly for sites across Asia, from the extreme east of Europe eastwards to Japan and places at similar longitudes, but with the possibility of some unusual activity at almost any stage from ~ 6h-24h UT on November 17, only European and African longitudes look set to miss out. Even here, radio coverage of the shower will be possible for part of that time. Of course, other possible maxima are not excluded (look out for updates nearer the time), and observers should be alert as often as conditions allow throughout the shower, in case something unexpected happens. All observing techniques can be usefully employed.
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