Saturday, October 21, 2006
Viewing the 2006 Orionid Meteor Shower
This represents the view from mid-northern latitudes at about 1:00 a.m. local daylight time around October 21. The red line across the bottom of the image represents the horizon. (Image produced by Gary Kronk using SkyChart III 3.5 and Adobe Photoshop 5.5.)
The Orionid meteor shower is active throughout October and the first week of November. This shower is produced by the inbound particles of the famous Halley's Comet, which last passed through the inner solar system in 1986. The Earth passes closest to the comet's orbit on October 21. At this time the Earth actually only skims the outer fringes of the debris field produced by Halley's Comet. The Orionids can still produce a very entertaining display of celestial fireworks, especially when viewed from rural locations. When seen near maximum activity, an observer from a rural location can count 15 to 25 Orionid meteors per hour.
As October arrives, the first of the Orionid meteors may be noticed. At this time the radiant (the area of the sky where the Orionids seem to originate) is located in northern Orion, just a few degrees north of the tight little group of stars formed by Lambda and Phi Orionis. As the month progresses the radiant travels slightly less than one degree toward the northeast each night. On the morning of maximum activity, October 21, the radiant is then located on the Orion/Gemini border, three degrees west of the bright star Alhena (Gamma Geminorum). As we pass into November the radiant has moved well within the constellation of Gemini. The last traces of the Orionid meteor shower may be seen near November 7 when the radiant lies in south-central Gemini near the faint star Lambda Geminorum.
In mid-October the constellation of Orion rises near 2300 (11pm) local daylight time. LDT is your time local regardless of location. You may see meteor activity during the early evening hours, but they will certainly not be Orionids! The Orionids (like all meteors) cannot be seen until they strike that portion of the atmosphere that is visible from your observing site. This can only occur when the radiant has an elevation of -5 degrees or higher. Minus 5? Yes, meteors can actually be seen when their radiant is slightly below the horizon. At this altitude meteors are able to just skim the upper regions of the atmosphere that is visible from your observing site. These meteors are rare and best seen during the strongest showers. You may get lucky and actually see an Orionid "earthgrazer" during the late evening hours. These meteors are different than your average "shooting star" in that they are very long and also long-lasting. The brightest ones can stretch from horizon to horizon, lasting five seconds or more (an eternity compared to the average duration of 0.3 seconds).
As the night progresses the constellation of Orion and the Orionid radiant will climb higher into the sky. The average Orionid meteor will become appear progressively shorter and faster as they strike the dense portions of the upper atmosphere. The radiant will culminate near 0500 LDT, when it lies on the meridian. This will be the best time to see Orionid activity as the radiant will then be located highest above your horizon. To best view Orionid activity look in the general direction of the radiant with the bottom of your field of view situated just above the horizon. Avoid looking straight up as this direction has the thinnest slice of atmosphere. That's great for telescopic work but not for viewing meteor activity. Aim your view a bit closer to the horizon and you will be viewing though a much thicker slice of the atmosphere, allowing you to see more meteor activity. I would also recommend that you not look directly at the radiant as the meteors seen there are short and easily missed. Keep the radiant off to one side of your field of view, but close enough easily tell the meteor came from Orion. Looking in this direction will also help you see the slow Taurid meteors coming from the west and the swift meteors from Leo Minor, coming from the east. Besides these radiants one can also expect up to fifteen random meteors occurring each hour. This offers a good opportunity to see a wide variety of celestial fireworks, if one can stay awake during the early morning hours. ...
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