Meteor Showers

The night of the Geminids' peak, 14 December. The ring is the shower's radiant, beside Castor and Pollux in Gemini: trace any of tonight's shower meteors backwards and it points here. The readout is the radiant's height, and that height is most of what you will count.

Why one point? The meteors are grains shed by 3200 Phaethon, all flying along one orbit, so they reach the air on parallel tracks at 35 km/s. Parallel lines seen in perspective fan out from one vanishing point, like rails. Streaks appear anywhere in the sky — like the arrows — but all point back to the ring.

Now run the night. The radiant is low in the east at dusk and climbs until the small hours. A meteor can only come from above the horizon, so with the radiant low most tracks are lost below it. The count rises all night — and the best hours of almost every shower are after midnight.

The night as a graph. The rule is the published ZHR, 150 an hour: a perfect sky with the radiant overhead. The dashed curve is a perfect sky with the radiant where it is. The solid one is a suburban Bortle 5 sky, with the Moon.

How to watch: a dark site, lie back, and look about 40° from the radiant, not at it — meteors near the radiant come almost head-on and are short. No telescope: they are anywhere. Then wait. Your eyes need twenty to thirty minutes of dark to reach full sensitivity, and a bright white screen sets them back.