Thursday 3 May 2012

The eta Aquarid Meteors.

The eta Aquarid Meteor Shower peaks on (or about) 6 April each year, when the Earth passes through the orbital path of Halley's Comet; the meteor shower is caused by material from the comet's tail hitting the planets atmosphere and burning up. This occurs even though the comet is not currently close to us - it last visited the Inner Solar System in February 1986 and will not return until July 2061. The comet has been on its current orbit for at least 16 000 years (possibly as long as 200 000 years), and during this time a lot of material has been shed from its tail, and continues to follow roughly the same orbital path.

The orbit of Halley's Comet. University of Alaska Fairbanks.

Halley's Comet visits the Inner Solar system every 75-76 years, making it a short period comet; long period comets return to the Inner System less than once every 200 years. At its closest to the Sun it reaches a distance of 0.6 AU, 60% of the distance at which the Earth orbits the Sun, between the orbits of Venus and Mercury. At its furthest it reaches 35 AU, roughly the average orbital distance of Pluto. During each visit it crosses the orbital path of the Earth twice, creating two yearly meteor showers, the eta Aquarids in May and the Orionids in October.

The eta Aquarids are named for the point in the sky at which they originate, close to the star Eta Aquarii. They are best seen from the Southern Hemisphere, as the point of origin is close to the horizon in the Northern Hemisphere, though the display is likely to be poor in 2012, due to a bright Moon. At the peak of the shower about 30 meteors an hour should be visible. The visible meteors are tiny particles burning up high in the atmosphere, it is highly unlikely that any material from the shower could ever reach the ground (a meteor is a shooting star, an object visible in the sky; a meteorite is a piece of rock on the ground of extra-terrestrial origin).

The point of origin of the eta Aquarid Meteor Shower. NASA/

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