Perseids 2015

This week marks the peak of the Perseids Meteor Shower – one of the best meteor showers of the year, typically producing up to 60 meteors an hour at its peak. This year’s shower should peak on August 11, 12 and 13 but we should be able to see some meteors any time over the next 2 weeks. Look for fast moving streaks of light, about as bright as a star, although you may get lucky and see a fireball – a very bright meteor with a small disk. Try to find a pretty clear, unobstructed view of as much of the sky as you can manage – trees and buildings can really block the view, and of course, the darker the sky, the better.

This meteor shower is named for the constellation Perseus, but you don’t need to be able to spot that constellation, since the meteors can appear anywhere in the sky. Only if you record the path of any meteor you see, might you be able to trace the paths back towards Perseus high in the north east. Most meteors are likely to be seen in the early hours, after midnight, as our section of the Earth turns into the dust and debris sitting in the Earth’s orbit.

Meteors are tiny bits of dust, in this case linked to Comet Swift-Tuttle. This comet was discovered independently by Swift and Tuttle in 1862 and has a period of about 128 years. It was linked with the Perseids at the time, but the exact orbit of this comet was tricky to work out. It was predicted to return in 1982 or possibly 1992, the difference due to the fact that there were two earlier 18th century comets that could have been the same comet. Each earlier comet gave a different year when used in the calculations.

It was looked for in 1982, but only appeared in 1992 – and about 17 days out from the predicted time frame. This was not due to any error in the mathematics – but likely due to a slight break up of the comet as it had passed near the sun, causing it to alter its orbit. As it swooped in close to the Sun on this orbit, it shed a lot of dust in its wake – this dust is what burns up in the Earth’s atmosphere in a meteor shower. For a few years after 1992, there were up to 300 Perseid meteors seen per hour, but it is uncertain what kind of a shower we are due for this year. 2028 looks to be promising, with the Earth due to pass directly through a major debris pocket of the comet.

Calculations made in the mid 90s on the orbit of Swift-Tuttle raised the possibility that it might pass very close to the Earth in 2126, or even hit us. This has since been revised to a much more comfortable distance of over 20 million kilometres – barely enough to raise any alarm, although the views of it are due to be spectacular!

The header image is of the 2010 Perseids, seen above ESO’s Paranal Observatory in Chile.  Credit ESO/S. Guisard

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