Leonids (LEO)
Active: November 10–23;
Maximum: November 17, 21h15m UT (nodal crossing at λˆ = 235 .°27), but see below;
ZHR = 20?;
Radiant: α = 152g, δ = +22°;
Radiant drift: see Table 6;
V∞ = 71 km/s;
r = 2.5;
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);
α = 120°, δ = +20° before 4h local time and α = 160°, δ = 00° after 4h local time (β > 00° N);
α = 120°, δ = +10° before 0h local time and α = 160°, δ = −10°(β < 00° 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 recently. This year is not expected to produce enhanced rates, but theoretical work by Mikhail Maslov suggested peak ZHRs of ~ 20 might occur around November 17, 15h UT instead of at the usual nodal crossing time above. ZHRs from that later possible peak are likely to be ~ 10–20. The waxing gibbous Moon will not set until 2 to 3 a.m. local time on November 17 across the mid-latitude globe (later moonsets for places further north). As the Leonid radiant rises usefully only around local midnight (or indeed afterwards south of the equator), there will still be plenty of dark-sky time between moonset and the onset of morning twilight to observe whatever happens this year. The ~ 15h UT peak timing would coincide with moonless skies from the extreme east of Russia east to Alaska and places at similar longitudes on the Pacific Ocean. The ~ 21h UT timing would favour locations at comparable longitudes to central-eastern Asia, from roughly India east to Japan/western Australia. Other possible maxima are not excluded, 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. VID indicated Leonid activity might be detected that way from about November 8–28, though this remains unconfirmed visually.