Space Notes

Reference

The nine showers worth
staying up for

Every year brings a few dozen recognised meteor showers. Nine of them produce enough meteors to justify a cold hour in a deck chair. These are those nine.

Annual peaks

Peak dates shift by up to a day between years. Rates are zenithal hourly rates: what a single observer would see under a genuinely dark sky with the radiant overhead. Expect a third of that on a normal night.

ShowerPeakActive periodZHRSpeedParent body
Quadrantids3–4 Jan28 Dec – 12 Jan11041 km/sasteroid 2003 EH1
Lyrids22–23 Apr16 – 25 Apr1849 km/scomet Thatcher
Eta Aquariids5–6 May19 Apr – 28 May5066 km/scomet 1P/Halley
Delta Aquariids30 Jul12 Jul – 23 Aug2541 km/scomet 96P/Machholz
Perseids12–13 Aug17 Jul – 24 Aug10059 km/scomet 109P/Swift–Tuttle
Orionids21–22 Oct2 Oct – 7 Nov2066 km/scomet 1P/Halley
Leonids17–18 Nov6 – 30 Nov1571 km/scomet 55P/Tempel–Tuttle
Geminids13–14 Dec4 – 17 Dec15035 km/sasteroid 3200 Phaethon
Ursids22–23 Dec17 – 26 Dec1033 km/scomet 8P/Tuttle

Reading the table honestly

ZHR is a ceiling, not a forecast

It assumes the radiant is at the zenith and the faintest visible star is magnitude 6.5. Drop the radiant to 30° above the horizon and you lose half. Add suburban skyglow and you lose most of the rest.

After midnight is not superstition

Before midnight your side of the planet faces away from its direction of travel, so you only catch meteors that overtake the Earth. After midnight you face forward and sweep them up head-on.

Speed shapes what you see

The fast showers — Leonids, Orionids, Eta Aquariids, all above 60 km/s — leave persistent trains that hang for a second or two. The slow Geminids produce long, deliberate streaks that are easier to point at.

Two of them come from rock

Quadrantids and Geminids trace back to asteroids rather than comets. The Geminids are also the youngest major stream, and by far the most reliable in a bad year.

Practical method

Lie back so the sky fills your field of view, pick a patch about 50° away from the radiant, and stay there. Meteors near the radiant are foreshortened to short stubs; the long ones appear well off to the side. Do not use binoculars — the field is far too narrow.

Count in fixed blocks, an hour at a time, and write down the clock time of every meteor. Rates vary enough between half-hours that an impression formed over ten minutes is worthless.

Moon first, shower second. A shower peaking three days either side of full Moon is not worth a long drive. Check the phase before you check the peak date — a quiet night with a dark sky beats a rich one washed out by moonlight.