The Andromedids meteor shower
Key facts
- Peak
- around 27 November historically; now weak, in late November to early December
- Active
- late November to early December
- Rate at peak (ZHR)
- usually under 2; storms of thousands an hour in 1872 and 1885
- Speed
- about 19 km/s
- Radiant
- Andromeda and Cassiopeia (historically near Gamma Andromedae)
- Parent body
- Comet 3D/Biela (broken up and lost since the 1850s)
Dates shift slightly from year to year. This year's peak is in the events calendar.
The Andromedids, also called the Bielids, are the ghost of a comet. In the nineteenth century they produced two of the greatest meteor storms ever seen. Today they are almost gone, but they taught astronomers that comets can fall apart and turn into meteors.
The parent comet. The comet was first seen in 1772. In 1826 an Austrian army officer and amateur astronomer, Wilhelm von Biela, recovered it and showed that it returned about every six and a half years, so it was named after him. In late 1845 and early 1846 observers saw it split into two comets travelling side by side. Both pieces returned in 1852, further apart. After that, the comet was never seen again.
The storms. Biela's orbit crossed Earth's in late November. On 27 November 1872, when the comet should have been passing, Europe saw a meteor storm, with thousands of slow meteors an hour radiating from Andromeda. On 27 November 1885 the storm was even stronger, with estimates of many thousands an hour. The lost comet had become a cloud of dust.
On 27 November 1885, during the storm, an iron meteorite fell at Mazapil in Mexico. For a while some people thought it was a piece of Biela's comet. It was a coincidence: iron meteorites come from the cores of asteroids, not from comets, and shower meteoroids are far too small and fragile to reach the ground.
Since then. Displays of a few hundred an hour occurred in 1892 and 1899, then the shower faded as planetary gravity moved the stream. Forecasters predicted that Earth would meet old Biela dust in early December 2011, and radar and cameras duly recorded a small outburst of faint meteors. The radiant has shifted from Andromeda towards Cassiopeia.
What to expect. Very few meteors in most years; slow ones, at about 19 kilometres per second.
Viewing. The radiant is high in the evening from the UK and northern countries. It is poorly placed from the southern hemisphere.
Viewing tips
- Watch in the evening, when Andromeda and Cassiopeia are high overhead.
- Find the W of Cassiopeia and the chain of Andromeda's stars below it.
- Look for slow meteors that drift across the sky.
- Check forecasts for predicted encounters with old Biela dust.
- Remember that shower meteors never reach the ground as meteorites.
Read about the parent: Comet Biela, and the other comets behind meteor showers.