The Tau Herculids meteor shower
Key facts
- Peak
- around 30–31 May, mainly in outburst years
- Active
- late May to early June
- Rate at peak (ZHR)
- usually very low; about 60 during the outburst of 31 May 2022
- Speed
- about 16 km/s
- Radiant
- Historically Hercules; in 2022 Boötes, north-west of Arcturus
- Parent body
- Comet 73P/Schwassmann–Wachmann 3
Dates shift slightly from year to year. This year's peak is in the events calendar.
The Tau Herculids are a shower from a comet that broke apart. For most of the time since its discovery they have been barely detectable, but in 2022 debris from the comet's break-up gave a memorable outburst.
The parent comet. Comet 73P/Schwassmann–Wachmann 3 was discovered in 1930 by two German astronomers, Arnold Schwassmann and Arno Arthur Wachmann, while they were photographing the sky to search for asteroids. It orbits the Sun about every five and a half years. In 1930 it came within about 9 million kilometres of Earth, and observers in Japan reported meteors from a radiant near the star Tau Herculis, which gave the shower its name. The comet was then lost for decades before being recovered.
In 1995 the comet suddenly brightened and split into several pieces. By its 2006 return it had broken into dozens of fragments, some of which were photographed falling apart by the Hubble Space Telescope. A comet that shatters releases far more dust than usual, and forecasters calculated that dust from the 1995 break-up would reach Earth on 31 May 2022.
The 2022 outburst. The forecast was right. On 31 May 2022 observers, mainly in North America where it was dark, saw a two-part peak with rates equivalent to about 60 meteors an hour, centred around 04 to 05 hours Universal Time. The meteors entered the atmosphere at only about 16 kilometres per second, so most were faint, though some bright meteors and a fireball were recorded. Because Earth met fresh debris, the radiant was not near Tau Herculis but in Boötes, north-west of the bright star Arcturus.
What to expect. In most years, very few meteors. Further encounters with debris from the comet are possible in coming decades, so watch for forecasts.
Viewing. The 2022 radiant was well placed from the UK in the evening, but the peak fell around or after British sunrise. Northern summer twilight also hampers faint meteors in northern Britain. Any future outburst will favour whichever part of the world has darkness at the predicted time.
Viewing tips
- Look out for forecasts, as activity depends on meeting debris from the 1995 break-up.
- Find orange Arcturus by following the curve of the Plough's handle.
- Expect slow, faint meteors and pick the darkest site available.
- Leave a camera running through the predicted time to catch faint members.
- Note the exact time of any meteor, because outbursts last only a few hours.
Read about the parent: Comet Schwassmann–Wachmann 3, and the other comets behind meteor showers.