What are Earth-grazing meteors?

When a shower's radiant is just above the horizon, its meteors skim the upper atmosphere at a shallow angle and leave long, slow-looking trails across the sky. Early Eta Aquariids, seen when the radiant has only just risen, are often of this kind.

Why does the shower have such a long name?

Showers are named for the constellation, and sometimes the star, nearest their radiant. The Eta Aquariid radiant lies close to Eta Aquarii, a star in the constellation Aquarius.

Is it worth watching the Eta Aquariids from Europe or North America?

Yes, with modest expectations. From mid-northern latitudes the radiant rises only shortly before dawn, so rates are low, perhaps 10 to 20 per hour at best. Southern and tropical observers usually see two or three times as many.

Eta Aquariid Meteor Shower: Dates and Tips

Eta Aquariid meteor shower at a glance

Detail	Value
Activity window	about April 19 to May 28
Peak	around May 6
Zenithal hourly rate (ZHR)	about 50 (varies, roughly 40 to 85)
Radiant	Aquarius, near the star Eta Aquarii
Parent body	comet 1P/Halley
Entry speed	about 66 km/s

These values follow the calendar of the International Meteor Organization (IMO). For every shower in one place, see the meteor shower calendar.

A second shower from Halley’s Comet

Comet 1P/Halley orbits the Sun about every 76 years. Over thousands of years it has shed a broad stream of dust along its path. Earth’s orbit passes near that stream twice a year. In early May we cross one side and see the Eta Aquariids. In October we cross the other and see the Orionids.

Both showers have the same parent and similar fast meteors, but the Eta Aquariids are usually the stronger of the two for observers well placed to see them.

Why the Southern Hemisphere has the advantage

The radiant in Aquarius rises only a few hours before the Sun in early May. From southern and tropical latitudes it climbs fairly high before dawn, so observers there can see a good share of the shower. From mid-northern latitudes, such as most of Europe, the United States and Canada, the radiant is still low when morning twilight begins, and many meteors are lost below the horizon.

That is why the ZHR, which assumes the radiant is overhead, can be misleading. A ZHR of 50 may translate into 20 to 40 meteors an hour in the Southern Hemisphere on a good morning, but only about 10 in northern locations.

Fast meteors and persistent trains

Like the Orionids, Eta Aquariid particles meet Earth at about 66 km per second. Many are bright, and a good proportion leave persistent trains: glowing trails that remain visible for a second or more. The maximum is broad, with good rates for several days on either side of May 6.

When and where to look

The best time is the last two hours or so before the start of morning twilight, when the radiant is as high as it gets before the sky brightens. You can check when twilight begins with the sunrise and sunset times for your location.

Look toward the east, then up. Meteors can appear anywhere, and those farther from the radiant have longer paths. Facing east and looking about halfway up the sky is a good choice.

Moonlight

The Moon’s phase can make a big difference. A bright Moon in the morning sky will hide many of the fainter meteors. Check the moon phases for early May and the moonrise and moonset times to see whether the Moon is up before dawn. Since the peak is broad, a morning a few days away from the maximum can be better if it is darker.

Viewing tips

Set an alarm. This is an early-morning shower; evening watching shows almost nothing.
Find a clear eastern horizon. Trees or buildings in the east block the low radiant.
Get away from light pollution. Dark skies show many more of the fainter meteors.
Let your eyes adapt. Spend 20 to 30 minutes in the dark without screens.
Use no optical aid. The naked eye covers the most sky.
Try several mornings. Rates stay fairly good for a few days around the peak.