October 20, 2012 2 Comments
Everyone know that the most famous comet is Comet Halley. Once every 76 years or so, Hally visits the inner Solar System. Sometimes is can be quite spectacular (such as in 1910), other times not so much (as in 1986). For those that missed Halley in ’86, it will be back again in 2061. If you don’t want to wait that long, there is a way to see pieces of Halley every year. Dust released by Halley over the past few thousand years produce meteor showers in early May (the η-Aquariids) and mid-October (the Orionids).
Computer simulations of the past movements of Halley and its dust suggest that many of this year’s Orionid meteors were released by Halley between 1265 BC and 910 BC (for some points of reference, the Trojan War took place around 1200 BC and King David ruled around 1000 BC).
This year the Orionids are forecast to peak tonight (Oct 20/21) though this shower usually produces high rates for a few days on either side of its peak time. According to the Live ZHR page on the International Meteor Organization’s page, rates last night reached a ZHR of 20-30. Tonight rates should be a little better, probably between 30-40. ZHR’s been as high as 70 per hour in the past but during the last 2 years ZHRs only reached 35-45 per hour. This year’s activity should be similar to the last few years.
The Orionids appear to come from an area in northern Orion. This area, called the radiant, rises around 10pm local time. It is best to wait till the radiant is high in the sky before looking for meteors (say 1am). The radiant is highest around 3:30am which is the best time to look. Meteors can appear anywhere in the sky so you don’t have to look at the radiant. The chart below is for around 3-4am local time and shows the radiant and directions of the Orionids.
Hints for watching the Orionids:
- Orionid meteors are not visible before ~10-11 pm. Even then the radiant is too low to see many meteors. It is best to go out sometime between 2 am and the start of dawn.
- Even though the Zenithal Hourly Rate (ZHR) for the Orionids may be as high as 40 per hour this year. Most people will see fewer meteors. The ZHR is calculated for perfect conditions (radiant overhead, dark skies, and no obstructions in your view). If you observe from rural areas where the Milky Way is bright and obvious you might see 40 per hour. Suburban skies were the Milky Way is just barely visible will probably only produce 10-20 per hour. City observers will see only a few per hour.
- It may take some time to see some meteors. Going out for a minute or two won’t cut it. Plan to spend at least 30 minutes of more outside. Also allow your eyes some time to get adapted to the dark. It will take at least 10-20 minutes after walking out of a well-lit house to start seeing faint enough to see most Orionids.
- Find a spot that is safe, free of as many obstructions (trees, buildings, etc) as possible and free of annoying lights shining in your face. This is not always possible these days. You don’t need to look directly at the radiant. In fact, it is better to place the radiant just outside your field of view. As long as you do this, it won’t matter what direction you look in.
- Be prepared to be cold. The early October mornings can get very chilly. Dress warm and bring a blanket. Also plan to be as comfortable as possible. A nice reclining chair works great. It will keep your neck from being strained and keep you off of the cold ground.
- Enjoy the show! The split second meteors are tiny dust grains from Comet Halley released thousands of years ago; are hitting the Earth’s atmosphere at speeds of ~40 miles per second (~66 km per second) and are burning up 60 miles (100 km) above your head.