★ Eta Aquariid Meteor Shower

The Eta Aquariids are one of two meteor showers made by Halley's Comet; the other is the Orionids in October. They bring fast meteors, often with glowing trains, in the last hours before dawn in early May. For the tropics and the Southern Hemisphere they are one of the best showers of the year.

Where the meteors come from

The parent is 1P/Halley, which goes around the Sun about every 76 years. Each time it returns, its very dark nucleus, about 16 by 8 by 8 km, sheds ice and dust along its orbit. Earth passes through this debris twice a year: in early May, giving the Eta Aquariids, and in October, giving the Orionids. The grains hit the atmosphere at about 66 km/s. Halley last passed through the inner solar system in 1986 and will not return until 2061, but its dust arrives every year.

When to watch

The shower runs from April 19 to May 28, with a broad maximum around May 6. The table above gives the expected peak time and the Moon.

The radiant rises in the east only around 2 to 3 a.m. and would be highest around 8 a.m., in daylight, so the best time is the last two hours before morning twilight. Observers in the tropics and the Southern Hemisphere have longer nights at this time of year, so the radiant gets higher before the sky brightens. IMO notes that useful observations are possible from anywhere south of about 40°N.

How to find the radiant

The radiant lies in Aquarius, right next to the star Eta Aquarii, one of four stars that form the Water Jar, a small Y-shaped pattern. Aquarius has no bright stars, so use the Great Square of Pegasus as a guide: seen from northern latitudes before dawn, the Square is rising in the east, and the Water Jar is to its right and slightly lower, about two fist-widths at arm's length from Markab, the Square's right-hand corner star. Face east.

From about 40°N the radiant is only about 15 to 20 degrees up when morning twilight begins; from around 30°S it reaches 40 to 45 degrees. Meteors seen soon after the radiant rises are often Earthgrazers, long meteors that skim across the sky almost parallel to the horizon.

What to expect

IMO gives a peak ZHR of about 50, ranging from about 40 to more than 80; recent years have come in nearer 40. From the tropics or the Southern Hemisphere, a dark rural site can give about 20 meteors an hour before dawn, sometimes more, and the suburbs 5 to 10. From mid-northern latitudes, about 10 an hour from a dark site is a good result, and only a few from the suburbs.

The meteors are fast, at 66 km/s, and a population index of 2.4 means a fair share of bright ones. Some leave glowing trains that last several seconds, occasionally minutes.

Viewing tips

• Set an alarm and be in place well before the sky starts to brighten.
• Choose a site with a low, open eastern horizon.
• Watch on several mornings in early May; the broad maximum gives you more than one chance.
• From the north, scan near the eastern horizon for Earthgrazers as well as higher up.

History and notable displays

Halley's Comet has been recorded for more than 2,000 years; one of its returns appears on the Bayeux Tapestry, which shows the Battle of Hastings in 1066. In 1705 Edmond Halley noticed that the bright comets of 1531, 1607 and 1682 had similar orbits, proposed that they were one comet, and predicted its return in 1758.

IMO analyses of visual observations going back to 1984 have found no regular cycle in the peak rate. In 2008, resonant meteoroids, grains whose orbits keep them bunched together, pushed the peak ZHR to about 85. Since then it has generally declined, from 70 in 2009 to 50 in 2019 and 2020 and roughly 40 in the most recent years, with a preliminary 35 in 2026.