The Perseids meteor shower
Key facts
- Peak
- around 12–13 August
- Active
- about 17 July to 24 August
- Rate at peak (ZHR)
- about 100
- Speed
- 59 km/s
- Radiant
- Perseus
- Parent body
- Comet 109P/Swift–Tuttle
Dates shift slightly from year to year. This year's peak is in the events calendar.
For many people the Perseids are the meteor shower. They arrive in the middle of summer, when evenings are warm and holidays give time to stay up late, and they are rich and reliable. If you have only ever seen one meteor shower, it was probably this one.
People have watched the Perseids for nearly 2,000 years. In parts of Europe they became known as the Tears of St Lawrence, because they appear around 10 August, the feast day of Lawrence, a Roman deacon martyred in the third century. The meteors were imagined as sparks or tears falling from the sky in his memory.
The scientific story is just as remarkable. In 1862 two American astronomers, Lewis Swift and Horace Tuttle, independently discovered a bright comet. Within a few years the Italian astronomer Giovanni Schiaparelli showed that its orbit matched the path of the Perseid meteoroids. It was one of the first times anyone had proved that a meteor shower is made of debris from a comet, and it transformed the study of meteors.
The parent comet. Comet 109P/Swift–Tuttle has a nucleus about 26 km across, large for a comet, and it orbits the Sun about every 133 years. It last passed close to the Sun in 1992 and will return in 2126. Over countless orbits it has laid down a broad river of dust, and every August the Earth ploughs through it. The particles are mostly smaller than a grain of rice, but they strike the atmosphere at about 59 km/s and blaze into light about 100 km above the ground.
What to expect. The ZHR at the peak is about 100, meaning that under perfect conditions an observer might see around 100 meteors an hour. In practice, under a good dark sky in the early hours, 40 to 70 an hour is a fine result. Perseids are fast, often bright and frequently leave glowing trains. The shower also produces a good number of fireballs. Activity builds gradually from late July, peaks around 12 to 13 August and then fades more quickly, so the nights either side of the peak are also well worth watching.
Viewing from the UK. The UK is one of the best places to see the Perseids. The radiant in Perseus lies in the north-east in the evening and climbs high overnight, so meteors appear all night long. Rates are lower in the evening and increase steadily after midnight, with the best hours usually from about 1 a.m. until dawn begins. In the far north of Scotland, August nights are still fairly bright, so southern Britain has slightly darker skies. Get away from streetlights if you can; a rural spot, a hilltop or a dark-sky park can triple the number you see.
Viewing worldwide. The Perseids are a northern hemisphere shower. Europe, North America and northern Asia all see them well. From the tropics they are lower and fewer, and from much of the southern hemisphere the radiant barely rises, so only a few long meteors appear low in the north before dawn.
You do not need a telescope or binoculars, which would narrow your view. All you need is a clear, dark sky, a comfortable place to lie back and some patience. Moonlight can wash out the fainter meteors, so the phase of the Moon makes a real difference. Exact peak dates vary slightly from year to year.
Viewing tips
- Watch after midnight, when the radiant is high and rates are at their best.
- Lie back on a reclining chair or rug and look at a wide area of sky, not just towards Perseus.
- Get away from streetlights and let your eyes adjust for at least 20 minutes.
- Try the nights either side of the peak too, because activity is good for several days.
- Bring a warm layer and insect repellent, because summer nights still turn cool.
Read about the parent: Comet Swift–Tuttle, and the other comets behind meteor showers.