The Orionids are best known as being one of two meteor showers associated with Halley’s Comet. This shower is active throughout October and the first week of November. A plateau of maximum activity is reached for several nights centered on October 22nd, when rates usually average 10-15 shower members per hour. Recently however, the Orionids have been quite strong, rivaling the rates produced by the Perseids of August. These strong displays have also been accompanied by fireballs, bright meteors that exceed the brightness of Venus.
The Orionids first begin appearing near October 4th. Rates slowly increase as the date of maximum activity draws near. With a full moon occurring on October 12th, moonlight will severely hamper pre-maximum Orionid observations. The last quarter phase, when the moon is half illuminated, will occur as the shower peaks on October 21st. The next two weeks will see dwindling Orionid activity and the last of the Orionids are seen near November 14th.
The Orionids cannot be seen during the early evening hours as the radiant is below the horizon until 2200 (10pm) local daylight time (LDT). Rates will be low prior to midnight as the radiant lies too close to the horizon. After midnight activity increases until the radiant culminates near 0500 LDT. During the short time between culmination and the beginning of morning twilight rates will slowly decrease as the radiant loses altitude. To best view the Orionids, choose a time when the radiant is located high in the sky. Face south half way up in the sky with the Orionid radiant at the left edge of your field of view. This will keep the moonlight out of your field of view. It is best not to stare directly at the radiant as Orionid meteors seen in this portion of the sky will be the shortest and may be missed. There are also other minor showers active during the Orionids. The Taurids to the west produce several slow meteors each hour. The Epsilon Geminids and the Leo Minorids, with radiants to the east average perhaps a meteor per hour. They both produce swift meteors like the Orionids.
In early October the Orionid radiant lies in northern Orion near the head of the great hunter. By the 21st the radiant has drifted into the “club” of Orion near the Orion/Gemini border. After maximum activity the radiant enters southwestern Gemini where it will be located until the display ends. Since the radiant lies close to the celestial equator the Orionids are seen equally well from both hemispheres. Those north of the equator may have a slight advantage as the radiant lies a bit higher in the sky (depending on your latitude) and the October nights are longer in the northern hemisphere.
These meteors strike the Earth’s atmosphere from nearly a head-on direction therefore most of them will appear to move swiftly through the sky. The exceptions will be Orionids that appear foreshortened near the radiant or those that appear near the horizon. While produced by particles released by Halley’s Comet, the current orbit of Halley’s Comet does not pass close to the Earth. Therefore the Orionids we see today were released by the comet many hundreds of years ago.
It is also enjoyable and scientifically useful to record the meteor activity you see. Experts in meteor astronomy can reduce your data and compare it to others all over the world if you use certain standards in your reporting. First and foremost is to provide the accurate time of your observing session. It is helpful to time each meteor but not absolutely necessary as long as the start and finish times are provided. The observing conditions are very important to properly record, especially if your field of view is obscured by clouds or trees. These obscurations should be recorded to the nearest ten percent. Once per session is fine for trees but at least every 15 minutes for changing conditions such as cloudiness. The limiting magnitude of the sky in your field of view should also be recorded at least once an hour. The easiest way to do this is to count the number of stars visible in pre-selected areas of the sky. These star count areas and the resulting equivalent limiting magnitudes are available online from the IMO web site at: http://www.imo.net/visual/major/observation/lm
It is also necessary to classify each meteor seen. Near October 22nd, a majority of the meteors seen will be Orionids. There is no way that every meteor is an Orionid that night. There are on average 10-15 random meteors occurring each hour. These can come from any direction and be of any velocity, usually slower than the Orionids. Orionids will always line up with the radiant in Orion and as mentioned before, will usually be swift unless they occur close to the radiant or close to the horizon. Other parameters that can be recorded are the magnitudes of each meteor, the color, the velocity (slow, medium, fast) and whether the meteor produced a persistent train. If you do decide to record data, be sure to share your data with one of the meteor groups such as the American Meteor Society.