by Anura Guruge
>> Lyrid meteor shower … — Apr. 20, 2013.
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The Eta Aquariids meteor shower, like all such showers, is an annual event; this one taking place between late-April and early-May.
As with all meteor showers, the meteors associated with shower are detritus left in the wake of comets; periodic comets such as Halley’s that make routine visits obviously leaving behind more matter in their trail each time they make a pass. The Eta Aquariids meteor shower is caused by the Earth crossing through the debris field left behind by 1P/Halley, with its 75.3 year orbital period, over the centuries.
Actually there is another meteor shower associated with 1P/Halley — that being the typically prolific, Orionids in late October. Having two showers associated with a ‘frequent’ visitor like Halley is to be expected. If nothing else, as should be fairly clear with all the attention that Comet ISON is getting, comet’s that are heading past Earth to circumnavigate the Sun have an inbound and outbound path, that crossed the Earth’s orbital path. So there are are two debris trails — and in the case of ISON, if it survives perihelion, Earth will be crossing those two paths, two weeks apart in January 2014. In the case of Halley, due to regular perturbations by Jupiter, its orbital path also changes, albeit not majorly, from trip to trip. So it, over the centuries, has laid down ‘rubber’ in different parts of the sky. Contrary to what you might read in the media, this meteor shower is not the result of Halley’s last apparition in 1986. It is debris left behind over the centuries.
Meteor showers, confusingly, are named after the constellation from which they appear to originate — though the constellation has nothing to do with the shower. It just provides astronomers with a reference as to where to find the shower. The constellation in this instance is Aquarius. Eta Aquariids the nearest distinguishing star, one of the brightest in the constellation.
I doubt whether I will get up that early to see this shower. I have seen quite a few in my time.
Halley on March 14, 1986, taken ‘close-up’ by European spacecraft ‘Giotto’ that was sent up as part of the ‘Halley Armada’ to meet-and-greet it. From NASA.