Meteors of the Eta Aquarid shower are most likely to be seen in the midnight-to-morning-twilight hours of May 5 and 6.
“Most likely” is an example of almost unavoidable ambiguity! The Eta Aquarids have on those nights their best chance of being seen, but they are not extremely likely to be seen. The shower is more favorable for south-hemisphere observers; and, this year, the Moon, not long past full, will be in the sky from not long after sunset until dawn.
These meteors are fragments, from dust up to pebbles or boulders, that separated from the mountain-like nucleus of Halley’s Comet, perhaps centuries ago, and are continuing in orbits that gradually diverge from the comet’s. The general orbit crosses inward over the October part of Earth’s orbit and outward south of the May part.
This is made clear by the space diagram in our web page on “Halley meteors.”
So we see the stream as the Orionid shower in October, and the Eta Aquarid shower in May.
The angle at which the stream approaches us determines the radiant, that is, the position in the sky from which the meteors appear to fly out. The radiant is slightly south of the celestial equator, near Eta Aquarii, one of the stars forming a distinctive small triangle, known as the Urn or Water-Jar of the constellation Aquarius the water-carrier.
Because these meteors are coming from in front of us and striking the advancing or morning side of Earth, the radaant does not come up into view until after midnight.
Here is the scene for an American location as the radiant climbs from the eastern horizon. Each hour, it will slope up higher, parallel to the celestial equator, so that more of the meteor streaks will be above the horizon.
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