The Orionids meteor shower
Key facts
- Peak
- around 21–22 October
- Active
- about 2 October to 7 November
- Rate at peak (ZHR)
- about 20
- Speed
- 66 km/s
- Radiant
- Orion (north of the bright star Betelgeuse)
- Parent body
- Comet 1P/Halley
Dates shift slightly from year to year. This year's peak is in the events calendar.
The Orionids are the autumn half of a pair. Together with the Eta Aquariids in May, they are made of dust from Comet Halley, the comet that returns about every 76 years and was last seen near the Sun in 1986. The Earth crosses near Halley's orbit twice a year, and in October we pass through the stream on the opposite side to the May encounter.
The connection with Halley was recognised in the nineteenth century, when astronomers noticed that both showers share an orbit very similar to the comet's. Halley itself has been recorded at every return since at least 240 BC, and over thousands of years it has shed enough dust to keep both showers going. When Halley returns in 2061 it will add fresh material, though it takes a long time for new dust to reach the part of the orbit the Earth crosses.
Fast meteors and lasting trains. Orionids enter the atmosphere at about 66 km/s, among the fastest of all showers. They are often bright, and a good share of them leave glowing trains, trails of ionised gas that can linger for a second or two, occasionally longer. On a good night you may also see the odd fireball.
What to expect. The Orionids are a modest but dependable shower. The ZHR is about 20, so under dark skies before dawn you might see 10 to 20 an hour. The maximum is broad and fairly flat, so several nights around 21 October give similar rates. Activity varies a little from year to year, and between 2006 and 2009 the Orionids were noticeably stronger than usual, with rates two or three times the normal level. This was traced to older clumps of Halley's dust, held in place by the gravity of Jupiter.
Finding the radiant. Orion is one of the easiest constellations to recognise, with three bright stars in a row forming the Hunter's belt. The radiant lies a little north of the reddish star Betelgeuse, close to the border with Gemini. You do not need to look straight at it; meteors can appear anywhere, but if you trace them backwards they will lead to this area.
Viewing from the UK. The UK is well placed. Orion rises in the east late in the evening in October and climbs into the southern sky by the early hours, so the best time is from about 1 a.m. until dawn twilight begins. Late October nights are long and often clear and crisp. The clocks go back at the end of October, a few days after the peak, so if you watch later in the shower check whether times are given in BST or GMT. Look south-east and south, about halfway up the sky.
Viewing worldwide. Because the radiant lies close to the celestial equator, the Orionids can be seen from almost everywhere on Earth. Observers in both hemispheres see similar rates, which makes this one of the most widely enjoyed showers. In the southern hemisphere Orion appears upside down compared with the view from Britain, with Betelgeuse below the belt, but the meteors are just the same.
The Moon's phase matters for a shower of this strength. Peak dates shift slightly from year to year, so check before you go out.
Viewing tips
- Watch from about 1 a.m. until dawn, when Orion is high in the south.
- Use Orion's belt to find the radiant, a little north of reddish Betelgeuse.
- Look out for glowing trains left behind by the fastest, brightest meteors.
- Try several nights around 21 October, because the peak is broad.
- The UK clocks go back a few days after the peak, so check whether times are in BST or GMT.
Read about the parent: Halley's Comet, and the other comets behind meteor showers.