Eta Aquariids: Halley's Comet in the dawn sky

Two showers from one comet

Halley's Comet circles the Sun every 75 or 76 years, and it leaves dust all along its path. Earth crosses that path twice a year: in early May, giving the Eta Aquariids, and in October, giving the Orionids. If you have never seen the comet, this is the nearest you can get.

The meteors are fast, hitting the atmosphere at about 66 km per second, and many leave glowing trains that last for seconds.

Why the south has the advantage

The radiant is near the Water Jar of Aquarius, close to the celestial equator. It rises only shortly before the Sun for people far north, so there is a narrow window before dawn with the radiant low. In the tropics and the south, it climbs much higher, and rates of 30 or more an hour are normal there.

Observers at mid-northern latitudes should expect more like 10 to 20 meteors an hour, though some of them are long, low skimmers.

An early start

A red-light torch preserves your night vision, and so does keeping your phone dim or away. Many people also find it pleasant to watch with a friend, taking turns to doze while the other counts, because the quiet early hours reward a patient pair of eyes.

• Set the alarm. The best time is the dark hour or two before the sky starts to brighten.
• Face east. That is where the radiant rises.
• Look for the grazers. When the radiant is low, meteors cross the sky in long, shallow arcs.
• Keep going to the end. Twilight comes quickly, but the last quarter hour is often rewarding.

An old story in the dust

Halley's Comet has been recorded since at least 240 BC, and was once seen as an omen of great events. Today we know it as a ball of ice and rock about 15 km long, and the meteors you see are particles smaller than a pea. The shower is broad, so the days around the peak also produce good rates. See the rest of the year on the meteor showers hub.