The Perseid meteor shower, clearly visible in night skies from late July to the end of August, is due to provide a spectacular show of meteors, otherwise known as shooting stars. These are tiny particles of dust from space that burn up in Earth's atmosphere, creating bright streaks across the night sky as they shoot across it. When Earth passes through the trail of a comet's orbit, hundreds of streaks of light in the sky are visible. Together, these are known as a meteor shower. The Perseids, named after the constellation from which they appear to radiate, Perseus, is often the most spectacular meteor shower in the Northern Hemisphere.

27th July 2022

Comet Swift-Tuttle

The comet responsible for the Perseid meteor shower is officially called 109P/Swift-Tuttle. Independently discovered by Lewis Swift and by Horace Parnell Tuttle in 1862, it orbits the Sun approximately every 133 years. With a nucleus about 26 kilometres (16 miles) wide, Comet Swift-Tuttle is the largest object known to repeatedly pass by the Earth. It last came near during its orbit around the Sun in 1992, and the next time will be in 2126. We see the Perseids every year, however, when the Earth cuts across the comet’s orbit, where debris left behind by the comet's passage enters our atmosphere.
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A comet is a large lump of ice mixed with dust and small rocky fragments. As it orbits the Sun, the ice sublimes—it changes directly from a solid to a gas. The gas is swept out into a tail behind the comet along with the dust and sand. These spread out along the comet's orbit forming a stream of debris known as meteoroids.

Such a stream, known the Perseid cloud, stretches along the highly elongated orbit of Comet Swift–Tuttle, where it has remained for many hundreds of years. Every year, from 17th July to 24th August, the Earth passes through the Perseid cloud, entering the densest, dustiest area on or around 12th August. As it does so, thousands of meteroids pour into the Earth's atmosphere.

Meteors

Most meteoroids are no bigger than a grain of sand. As they enter the atmosphere, travelling at speeds of 59 kilometres (37 miles) per second, they come into contact with its particles and ions. The meteoroids are quickly heated up by friction before burning up in a bright burst of light—known as a meteor or shooting star—streaking a bright path across the sky for a few seconds. Brighter meteors, made by larger, pebble-sized meteoroids, can create spectacular fireballs that blaze across the sky.

Radiant point

During a meteor shower, hundreds of meteors all appear to originate, or radiate, from a single point in the night sky, known as the radiant point. This effect is caused by streams of meteoroids entering Earth's atmosphere at high speeds in parallel paths (similar to parallel railroad tracks converging at a single vanishing point on the horizon). The Perseid meteors appear to come from the constellation Perseus, hence their name. The constellation—a pattern of stars that lie at vast distances away from us—is not the source of the meteors, but the point in the sky from where they appear to originate.

Seeing the Perseids

The shower is visible from mid-July each year as the Earth moves into the Perseid cloud, with the peak in activity around 12th August. During the peak, the rate of meteors normally reaches 100 or more per hour and can be seen all across the sky—not just in Perseus—from just before midnight until sunrise. Clearly visible in the Northern Hemisphere, they can also be seen in the Southern Hemisphere very close to the north horizon—from where they seem to hurtle upwards into the sky.