The annual Orionid meteor shower is peaking this week, with the best viewing opportunity for Australians falling in the early hours of Thursday morning. The shower, caused by debris shed by Halley's Comet as Earth passes through its trail each October, is active through to Saturday, but sky watchers are being urged to set their alarms early and temper their expectations due to a bright moon interfering with visibility.
When and Where to Watch the Orionid Meteor Shower
The prime window for catching meteors this week is between 3am and 4am AEDT on Thursday morning, with Wednesday night formally forecast as the best night overall. However, astronomers note some uncertainty around the exact peak, and reasonable numbers of meteors could still be visible as late as Friday or Saturday, though conditions are expected to deteriorate as the moon grows brighter.
The Orionids are effectively invisible before midnight because the radiant, the point in the sky from which the meteors appear to originate, has not yet climbed high enough above the horizon. Patient observers willing to stay up past moonset, which is expected around 2am to 3am, will have their best chance of catching the show.
University of Southern Queensland astronomer Jonti Horner recommends waiting until the moon has dropped below the horizon before heading out. "The moon doesn't set until 2 or 3am," he said. "While the moon's high in the sky, there's a lot more light pollution, which hides all but the brightest meteors."
City dwellers are not entirely out of luck. Brighter meteors should be visible from urban areas provided viewers position themselves away from direct streetlights.
Why This Year's Shower Could Be Quiet
Under ideal conditions, including dark skies and little moonlight interference, the Orionids typically produce around 20 to 30 meteors per hour. This year, a waxing gibbous moon is expected to wash out a significant portion of the fainter meteors, potentially cutting visible numbers by as much as half before it sets.
"This year will probably be a quiet one," Horner said, adding that anyone heading out early still stands a chance of seeing something worth the effort, though there are no guarantees.
Coinciding with the Orionids this year are the Northern and Southern Taurid meteor showers, which add a handful of extra meteors to the night sky. The two showers can be told apart by speed: Orionids are fast-moving streaks, while Taurids drift across the sky at a noticeably slower pace. "If you see one that was really fast, that was probably an Orionid," Horner said.
The Ancient Origins of the Orionid Shower
The Orionids carry a remarkable history. Horner says the shower has been observed for at least 2,500 years, with some historical records believed to date back to around 800 BC. The source of all that debris, Halley's Comet, is a ball of ice and dust that orbits the sun every 75 to 76 years. It last passed through the inner solar system in 1986 and is not expected to be visible from Earth again until mid-2061.
Each October, as Earth travels through the trail of particles left behind by the comet over countless orbits, those tiny fragments burn up in our atmosphere and produce the light streaks visible from the ground.
Tips for Getting the Most Out of the Viewing Window
- Wait until after the moon sets, around 2am to 3am AEDT, before heading out.
- The best viewing window is roughly 3am to 4am AEDT on Thursday, though Friday and Saturday remain possibilities.
- Find a spot away from direct streetlights, even in the city.
- Allow your eyes time to adjust to the darkness before scanning the sky.
- Look for fast-moving streaks to identify Orionids and slow-movers for Taurids.
Horner's overarching advice is to keep expectations in check. The shower may not deliver a spectacular display this year, but for those willing to brave the pre-dawn chill, even a handful of bright meteors can make for a memorable morning.
