Skywatch by Neil Norman

The Perseid Meteor Shower 2023

Everybody loves to see a meteor shooting across the night sky and all through the year you can witness sporadic meteors which appear to come from any direction at any time, but at certain intervals of the year more organised meteors can be seen in what is called meteor showers.

Meteor showers are created by comets that make close passes to Earth as they race in and away from perihelion, or their closest pass to the Sun. For example, the comet responsible for the Perseids is a comet named 109P/Swift-Tuttle which was discovered in 1862 but was originally observed as far back as 1737. The designation for the comet can be deciphered as follows; 109P/ indicates that it was the 109th comet of periodicity to be discovered. A comet must be observed on at least two separate returns to be given a designation and a definitive orbit to be determined and have an orbital period of under 200 years to be classed periodical. Swift-Tuttle refer to the discoverers, in this case both astronomers were American Lewis Swift and Horace Parnell Tuttle.

A comet can be imagined to be a dirty snowball hurtling through space on their trajectories taking them from deep frozen space until they return to the proximity of the Sun where Solar radiation warms them and volatile ices sublimate from their surfaces which also contains dust that create the distinctive tails associated with comets.

In the case of comet Swift-Tuttle, it is not so much a snowball it’s more a mountain as it is one of the largest known comets at an impressive size of 26 km in diameter. It also passes close to the Earth when it comes to perihelion and at closest can pass just 84,000 miles from us which in cosmic terms is a near miss.The comet last appeared in 1992 and will then return next in 2126. The dust lost at each return of the comet spreads around its orbit and due to that orbit passing close to Earth we pass through the densest part of the debris early on in August every year. These micro-sized pieces of dust hit the upper atmosphere at relative velocity of 17 km/s or 38,00 mph this causes great friction between the small body an atmosphere which leads to friction and the particles being vaporised some 40 miles above our heads but not before we see them as a brief glowing train speedily crossing the sky.

One of the best showers to occur during the year is that of the Perseids which can be seen from late July to late August each year with the peak of the showers activity, or best chance to see numerous meteors an hour, occurring on the night/morning of August 12/13.

On this night/morning one can expect to visually observe around 80 meteors an hour on a good clear night with no moon interference and no light pollution, obviously if the moon is near or at full phase and you live in a built up area your rate of meteors per hour will be greatly decreased. For 2023 the moon will be a slender crescent with just 6 percent of its surface illuminated and with it rising at 01.42 conditions will be perfect for observing.

The Perseids are some of the most beautiful meteors that you can observe and appear as soon as darkness falls in the direction of the constellation of Perseus which rises in the NE at this time. Also, this is a perfect shower to get all the family involved. The children will be on school holidays and it could be a great chance to offer an incentive to the child that sees the most meteors over the evening. It's also a great opportunity to learn a few of the constellations too.

Neil Norman (FRAS)