The Arids meteor shower
Key facts
- Peak
- around late September to early October, in some years
- Active
- late September to early October, when Earth meets fresh trails
- Rate at peak (ZHR)
- usually none; weak outbursts in 2021
- Speed
- about 15 km/s
- Radiant
- Ara (the Altar, in the far southern sky)
- Parent body
- Comet 15P/Finlay
Dates shift slightly from year to year. This year's peak is in the events calendar.
The Arids are a slow southern shower first seen in 2021 from dust released by comet 15P/Finlay. Their story shows how forecasters can predict a brand-new shower and watch it arrive.
The parent comet. Comet 15P/Finlay was discovered in 1886 by William Henry Finlay at the Royal Observatory at the Cape of Good Hope in South Africa. It is a Jupiter-family comet, orbiting the Sun about every six and a half years, on an orbit that does not pass far from Earth's. During its 2014–2015 return it had two sudden outbursts, flaring brightly as fresh material burst from its surface.
The 2021 encounters. Calculations showed that dust trails released by the comet in recent decades, and debris from the 2014 outbursts, would reach Earth in late September and early October 2021. Some forecasts suggested strong activity. Southern hemisphere video networks in New Zealand and Chile, and a meteor radar in Argentina, recorded the shower on 27–30 September, with a short peak on 29 September. Most of the meteors were faint. A second burst was recorded in early October from the debris of the comet's 2014 outbursts. The rates were far below the most optimistic forecasts, but the shower was clearly real and was named after its radiant in Ara.
Why so slow? The comet's orbit is very like Earth's in direction, so its dust arrives at only about 15 kilometres per second, one of the slowest entry speeds of any shower. Slow meteors glide across the sky, but they are also fainter than fast ones of the same size.
What to expect. In most years nothing. Future returns depend on further trail crossings, which forecasters will announce.
Viewing. Ara lies far south, below Scorpius, and never rises from the UK or most of Europe. It is well placed from Australia, New Zealand, southern Africa and South America in the evening.
Viewing tips
- Watch from the southern hemisphere in the evening, when Ara is high.
- Find the tail of Scorpius; Ara lies just south of it.
- Check forecasts, as activity depends on fresh dust trails.
- Use a sensitive camera, since many Arids are faint.
- Expect slow, gliding meteors if a return occurs.
Read about the parent: Comet Finlay, and the other comets behind meteor showers.