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See the Orionid meteor shower this weekend
BY MARK ARMSTRONG
ASTRONOMY NOW

Posted: 17 October 2012


Orionid Radiant The Orionids reach an optimum peak of 25 meteors per hour over 20-22 October. AN graphic by Greg Smye-Rumsby.

The annual Orionid meteor shower peaks over several nights close to October 20-22, which is favourable for this coming weekend. The shower is a result of debris shed by Halley's comet in its 75 year journey around the Sun, forming a stream of small particles (meteoroids) that the Earth ploughs through, the meteoroids burning up in the atmosphere. The stream is clumpy as a result of debris being shed from the comet at different times and occasionally the Earth encounters a more concentrated section, causing enhanced rates, as was the case in 2006. Orionids are swift moving, hitting the atmosphere at 60 kilometres per second and bright events around mag. +1 or brighter are not uncommon, many leaving persisting ionisation trails that never fail to thrill the lucky observer!

The good news is that the Moon will be well out of the way this year, setting mid to late evening just as the radiant, a few degrees north-east of Betelgeuse, is rising across the other side of the sky. Although not in the same spectacular class as the Perseids or Geminids, the Orionids are well worth making the effort to observe with observed rates of 10-12 meteors per hour under good conditions. However it does mean an early morning observing stint in the hopefully clear but cold air, the radiant rising around 9pm but not reaching a reasonable altitude until around midnight. By 3am the radiant is more than 40 degrees above the southern horizon and then the best rates should be seen.