Outburst of the Eta Aquarids?

Mikiya Sato and J. Watanabe (National Astronomical Observatory of Japan) forecast possible enhanced activity in the Eta Aquarid meteor shower on May 6, 2007. Their announcement appears on Electronic Telegram 944, issued to subscribers by the Central Bureau for Astronomical Telegrams.

In general, meteor-shower calendars have downplayed this year's Eta Aquarids because the shower's peak coincides with a waning gibbous Moon, and its glare will seriously reduce the numbers of meteors seen. Even under ideal conditions — a dark, moonless sky — observers in north temperate latitudes seldom see more than 20 Eta Aquarids per hour. They can be identified by the fact that their paths, extended backward, intersect at a radiant near Zeta and Eta Aquarii.

However, Sato and Watanabe find that a certain dust trail left by Halley's Comet in 836 BC, nearly three millennia ago, could encounter Earth between 13h and 15h Universal Time on May 6th. "This particular trail is so old," the circular notes, "that its shape is very complex due to the accumulated effect of the perturbations." As a result, the peak is not expected to be very sharp and could extend well before and after these times.

Sato and Watanabe's calculations were inspired by an unexpected outburst that many observers witnessed in the Orionid meteor shower on October 21, 2006, including some unusually bright fireballs. The Orionids and the Eta Aquarids are both produced by dust particles from Halley's Comet. Earth encounters these particles each year around October 21st and again around May 6th, on opposite sides of its orbit.

Check our meteor pages for general tips on monitoring meteor showers. Both the American Meteor Society and the International Meteor
seek reports of unusual as well as routine meteor activity; their sites have online forms for submitting observations.

While conditions aren't ideal for visual monitoring of this shower, Christian
Steyaert (Vereniging Voor Sterrenkunde, Belgium) points out that radio
observations are not hampered by moonlight or even daylight. Changes in Eta
Aquarid activity levels should show up in the data being gathered by a
worldwide network of radio meteor observers, whose results are continuously displayed and updated at radio.data.free.fr.

Please check the online version of this AstroAlert on Sky & Telescope's website for possible minor updates:

Any major updates will be announced via subsequent AstroAlert messages. Good luck, and clear skies!

Roger W. Sinnott

Senior Editor

Sky & Telescope