Meteor Showers

The peak of the 1998 Leonid meteor shower (rich in bright fireballs), shown in a four-hour time exposure through a fisheye lens, and taken by Juraj Toth of Modra Observatory. This photograph demonstrates how the meteors in a particular shower appear to emanate from a certain point in the sky called the radiant. On a given night, this radiant point will remain relatively stationary with respect to the background star constellations; but will rise, traverse the sky, and set in the same manner as the sun and moon.

• Viewing Activity from the 2008 Orionid Meteor Shower
• Meteor Shower Basics
• Major Showers Through the Year
• 2008 Meteor Shower Calendar
• Explanation of the 2008 Meteor Shower Calendar
• Additional On-Line Resources

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Viewing Activity from the 2008 Orionid Meteor Shower

This chart represents plotted Orionids (arrows) seen from 45 degrees north latitude while facing south near 5:00 a.m. local daylight time on October 21. This chart was created using SkyChart III Version 3.5.1 from Carina Software.

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This chart represents plotted Orionids (arrows) seen from 25 degrees south latitude while facing north near 5:00 a.m. local daylight time on October 21. This chart was created using SkyChart III Version 3.5.1 from Carina Software.

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The Orionids are best known as being one of two meteor showers associated with Halley's Comet. This shower is active throughout most of October and the first week of November. A plateau of maximum activity is reached for several nights centered on October 21, 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. Unfortunately rates this year are most likely to be back to normal. This is not caused by a prediction of lower rates, but rather the fact that the last quarter moon will be in the sky during this display. The half-illuminated moon will obscure the fainter meteors and will reduce counts.

The Orionids reach a zenith hourly rate of 1 near October 2. Rates slowly increase as the date of maximum activity draws near. After October 10, the waxing moon will begin to interfere and will retard the increase in rates. It will be difficult to view Orionid activity right up to the 21st. On the 21st, the moon will lie on the Cancer-Gemini border, not far from the Orionid radiant. Viewing close to the radiant will be highly discouraged as the moon will ruin your night vision. I would suggest viewing toward the northern or western portion of the sky. This will keep the moon out of your field of view. For those south of the equator, view toward the south or west. With the radiant out of your field of view, seeing Orionids will be easy as shower members will all be parallel and will also possess similar velocities. It will be impossible to filter out any members of the Epsilon Geminids but members of the Taurids will be easy to tell apart due to their much slower velocity. Most sporadic meteors will appear moving in different directions and have different speeds when compared to the Orionids.

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.

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 spend the remainder of its days. Since the radiant lies close to the celestial equator the Orionids are seen equally well from both hemisphere. 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 21st, 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 it with us by emailing them to our operations manager Robert Lunsford.

This is the last major shower of 2008 that does not coincide with the full moon. Not until the Quadrantids of January 2009 will a major shower peak under favorable conditions. Take every opportunity to view this display and to share your observations with us.

From earliest times, humankind has noticed flurries of meteors that seemed to emanate from points in the sky at particular times of the year. These flurries, now called meteor showers, are produced by small fragments of cosmic debris entering the earth's atmosphere at extremely high speed. Each time a comet swings by the sun, it produces large amounts of small particles which will eventually spread out along the entire orbit of the comet to form a meteoroid "stream." If the Earth's orbit and the comet's orbit intersect at some point, then the Earth will pass through this stream for a few days at roughly the same time each year, producing a meteor shower.

The peak of the 1997 Leonid meteor shower as seen from ABOVE, in Earth orbit, by the MSX satellite. 29 meteors were imaged over a 48 minute period entering the Earth's atmosphere. Note the roughly parallel paths followed by the meteors, with the entry angle increasing slightly over the period of the time exposure. Compare this figure to the one the top of this page, which shows how the shower appears from BELOW. (image courtesy of Peter Jenniskens)

Because meteor shower particles are all traveling in parallel paths (see the figure above), and at the same velocity, they will all appear to radiate from a single point in the sky to an observer below (see the figure at the top of the page). This radiant point is caused by the effect of perspective, similar to railroad tracks converging at a single vanishing point on the horizon when viewed from the middle of the tracks. This effect is illustrated in the photograph shown above. Meteors seen near the radiant are approaching the observer and will appear as short streaks in the sky. Meteors seen 45 to 135 degrees from the radiant are moving in a more parallel direction to the observer. These meteors will produce longer streaks in the sky. Those seen in excess of 90 degrees from the radiant are actually moving away from the observer and their paths will again shorten the further the are from the radiant.

Meteor showers are usually named for the constellation in which their radiant lies at the time of shower maximum. Thus, the Perseid meteor shower (peaking about August 12) will appear to radiate from the constellation of Perseus, while the Leonid meteor shower (peaking about November 17) will appear to radiate from the constellation Leo.

Specific suggestions for observing meteor showers may be found on our Visual Observing Program page.

The meteor showers discussed below recur each year; in some cases they have been recognized for hundreds of years. The name of the shower in most cases indicates the constellation from which the meteors appear. Also discussed are sporadic rates. Sporadic meteors are those random meteors not associated with a particular shower; they are the random detritus left over from the creation of the solar system or are old dispersed debris not recognizable today as shower meteors. Click on the shower names (when linked) for more detail on any given shower. For meteor observers, those located in the northern hemisphere have a distinct advantage as shower activity is stronger there than that seen by observers located south of the equator. The reason for this is that most of the major showers have meteors that strike the Earth in areas located far above the equator. As seen from the northern hemisphere these meteors would appear to rain down from high in the sky in all directions. From those situated in the southern hemisphere only a small percentage of this activity is visible. Any activity would appear to travel upwards from radiants located low in the sky.

There are a few meteor showers best seen from the southern hemisphere. These would include any radiant with a declination (celestial latitude) below -20 and those that reach maximum activity during the southern hemisphere's winter months (July-August-September). These showers would include the Alpha Centaurids, Gamma Normids, Pi Puppids, Piscis Austrinids, Delta Aquarids, Alpha Capricornids, Dec Phoenicids, and the Puppid/Velids.

The year begins with the intense but brief Quadrantid maximum (January 3/4). Its brevity combined with typically poor winter weather hampers observation. January overall has good meteor rates restricted to the last third of the night. Rates to 20/hour can be obtained. A large number of radiants spread along the ecliptic from Cancer to Virgo. This activity diminishes somewhat in February with the same areas active.

Late-night rates are fair in the first half of March, but become poor rather suddenly after mid-March. The very poor rates, seldom reaching 10/hour, continue into early June. However, two major showers appear in this interval. The Lyrids past mid-April (max: April 21/22) raise meteor rates for several nights. The Eta Aquarids (max: May 5/6) enrich late nights of May's first half, sometimes substantially.

February, March, and April evenings have another notable feature. An unusual number of sporadic fireballs come in this interval, possibly one every few nights.

June to mid-July has fair rates. The last half of July has rates increasing steadily as the Delta Aquarids (July 27/28) and Alpha Capricornids (July 30 - August 1) have maxima at month's end. Even the Perseids are beginning to show a little.

Overall, late July to mid-August is very rich in meteors. The Perseid maximum, just before mid-August (August 12/13), is fairly prolonged and quite rich.

High sporadic activity after midnight continues for the rest of the year, but especially in September and the first half of December. Sporadic rates over 20/hour are possible for this entire interval. September radiants are numerous in Aries and Taurus.

Mid-October to mid-December is a nearly continuous period of heavy meteor activity. The Orionids (max: October 21/22) during the second half of October have a prolonged, plateau maximum for several nights, usually rich. The Taurids (max: November 5/6 for S. Taurids, November 11/12 for N. Taurids), active for two months, are most numerous in November's first half, and can be rather variable in strength. This period is the best for a couple of Taurid fireballs each night, if the shower is not too weak. The Leonids of mid-November (max: November 17-19) are quite unpredictable, with rich displays occuring roughly every 33 years. The last Leonid storm period occurred from 1998 through 2002. The next enhancement for the Leonids is predicted in 2006, when rates may approach 60/hr. for a short time. Studies have shown that no Leonid storms will occur in either 2033 or 2066. We will have to wait until 2099 for a return of the activity recently seen during the past few years.

Finally the Geminids of mid-December (max: December 13/14) climax the year with the strongest dependable and observable display. Geminid rates usually pass 60-70/hour at maximum. Concurrent activity from Leo and Canis Minor is also notable during the Geminids. Finally, the oft-overlooked Ursids complete the year's activity, reaching maximum on December 21/22. Nearly half the year's visual meteor activity is crammed into the two-month interval just described.

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Additional On-Line Resources

• Comets and Meteor Showers, an internationally recognized site containing excellent historical and reference information on comets and meteor showers. Maintained by Gary Kronk.

• Frequently Asked Questions about Meteors and Meteor Showers, a FAQ sheet containing more in-depth information on this topic.

• Robert Lunsford's Weekly Meteor Outlook, a weekly newsletter describing the meteor shower activity for a given week.

• Visual Observing Program page, containing specific suggestions for observing meteor showers.

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Material on the AMS site © 2008 American Meteor Society, Ltd. All rights reserved.

Last Modified: August 31, 2008