Leonids

The tabulated ZHR is 12.5, which is a modest shower — around one meteor every five minutes at the theoretical best, and considerably less after the radiant-altitude correction. What the Leonids offer instead is speed: 70.3 km/s is the fastest of the twelve showers here, which produces bright, sharp meteors and a high proportion of persistent trains. In a dark-Moon year with a clear sky it is worth an hour. In a moonlit year it is not.

No forecast is made here. Leonid storms happen when Earth passes through a dense, recently released dust trail, which requires modelling the parent comet's ejecta trails forward in time. Historically they cluster near the perihelion passages of comet 55P/Tempel-Tuttle, which returns roughly every 33 years: 1833, 1866 and 1966 produced true storms, and the 1999 to 2002 returns produced outbursts with rates in the thousands per hour. The comet last passed perihelion in 1998 and is next due around 2031. The methodology page lists outbursts as an explicit limitation of this engine. The numbers on this site are the regular-activity baseline — a tabulated ZHR of 12.5 — and a specialist trail forecast, when one exists for a given year, is the better source.

The Geminids, comfortably, in an ordinary year: ZHR 150 against 12.5, and a radiant at declination +32.3° that is better placed for mid-northern observers than the Leonid radiant at +21.8°. The Leonids only become the better choice in a predicted outburst year, or when the Geminid peak falls under a bright Moon and the Leonid peak does not.

Between 2026 and 2030: 2028 are dark, 2027 and 2029 are washed out. With a base ZHR of 12.5 there is very little margin — a moonlit Leonid peak is usually not worth the lost sleep.

Not because of the speed itself, but the population index matters and for the Leonids it is 2.5. Each magnitude of sky brightness divides your count by that factor, so a two-magnitude suburban penalty costs roughly 6.3× the rate. The compensation is that fast meteors are more likely to be bright, so the ones that survive a compromised sky are the spectacular ones.

Judged only on how much of the Moon is lit at the peak instant: 2026 — 17 November 2026 (Moon 55% lit); 2027 — 18 November 2027 (Moon 80% lit); 2028 — 17 November 2028 (Moon 1% lit); 2029 — 17 November 2029 (Moon 90% lit); 2030 — 18 November 2030 (Moon 53% lit). The dark-Moon years are 2028; the washed-out ones are 2027 and 2029. Moon illumination is the only one of the four factors that is knowable years ahead — cloud cover is not, and neither is whether you will be somewhere dark.

Because 12.5 is the zenithal hourly rate: what one observer would count under a magnitude 6.5 sky with the radiant straight overhead. Two corrections pull it down before you ever look up. Rate scales with the sine of the radiant altitude, so a radiant 30° up delivers half of what it delivers at the zenith. And the population index for this shower is r = 2.5, which means each magnitude of sky brightness you lose costs you a factor of 2.5 in the count. A suburban sky two magnitudes shallower than the reference therefore divides the rate by about 6.3. Real counts are typically 30–50% under the modelled figure even after those corrections.