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The LEONID 
Meteor Shower

Up
How many meteors will we really see, and when?
Where do we have to go to see the Leonids?
What equipment do we need for observing?
For recording meteors, what should we record?
Where can we get more specialized information?
Leonids 2001 - November 17, 2001
Astro Geek's Leonids 2001 Report by Stephen LaFlamme
Leonids 2000
Leonids 1998 - Report by Brenda Culbertson.
ii) How many meteors will we really see, and when?

Predictions vary, depending on the researcher, the assumptions and methods used in the analysis, and the data analyzed.

Every 33.2 years, the parent comet passes around the sun in its orbit, and sheds debris. This debris takes on a slightly different orbit from the parent comet - and the debris shed in each subsequent comet return is laid down in a slightly different orbit. Over the years, we end up with a number of filaments or trails of debris, each in slightly offset orbits. When the earth passes through this area in space, it passes through a number of different trails at different times.

The researchers call each trail by the number of revolutions around its orbit that the dust has made since being shed. Some trails will produce more meteors than others. Some will have less debris in them and be almost insignificant - and the researchers may not quote meteor rates expected from those. The trails that are quoted in predictions this year are the 4-rev trail (debris from 1866), the 5-rev trail (debris from 1833), the 6- rev trail (debris from 1799) and the 7-rev trail (debris from 1767). The trails expected to produce the most meteors are the 4-rev trail and the 7-rev trail.

The meteor rates per hour are quoted as a Zenithal Hourly Rate (ZHR). This is the number of meteors, on average, that an observer would expect to see if they were out under a dark country sky, and if the radiant, the area in the sky where the meteors seem to come from, is directly overhead. Keep in mind that the peak of the Leonids falls on full moon this year - so the fainter meteors will not be as visible and the actual rates seen by observers will be lower than the quoted ZHR rate.

The time is quoted in Universal Time (UT) which is also the time at Greenwich, England. For observers in North America on Eastern Standard Time (EST), subtract 5 hours. For other time zones, adjust accordingly.

Note: Before we get into the storm predictions, note that there will still be regular Leonid activity occurring. The time of the maximum for the regular activity is listed by the IMO in their 2002 Meteor Shower Calendar as November 17th at 20h UT, ie. for observers on Eastern Standard Time (subtracting 5 hours) means 15h EST, which (subtracting 12) means 3 p.m. in the afternoon on November 17th. According to the IMO, "the November 17 timing favours places from Asia and Russia eastwards to the Far East and Australia."

The available storm predictions that most observers are aware of, as at the time of writing in late October, are the following. The storm components will occur a day and a bit later than the regular activity peak.

Note: When the duration of the trail peak is given, it is referring to 'full width half maximum' (FWHM), the period of time over which the rates are predicted to be at least half the maximum number of hourly meteors predicted. Hence observers should make sure to start watching ahead of time, and keep watching after the predicted time!

The team of Esko Lyytinen, Tom Van Flandern and Markku Nissenen predict (in ZHR rates):

  • Nov. 19 04.03 UT (11.03 pm EST on Nov. 18) 7 rev trail 3500/hr 
  • Nov. 19 06.36 UT (01.36 am EST on Nov. 19) 5 rev trail 160/hr 
  • Nov. 19 10.40 UT (05.40 am EST on Nov. 19) 4 rev trail 2600/hr

This team also mentions that the "7 rev trail meteors are brighter, so they are more easily seen in the sky brightened by the Moon" and that there may be a "possible weak 7 rev trail sub-peak" slightly before the main 7 rev trail peak. The 7 rev trail peak is predicted to last about 106 minutes, and the 4 rev trail peak about 122 minutes. More details are available at http://www.ursa.fi/ursa/jaostot/meteorit/leoeng02.html

Dr. Peter Jenniskens predicts (in ZHR rates):

  • Nov. 19 03.48 UT (10.48 pm EST on Nov. 18) 7 rev trail 5900/hr
  • Nov. 19 04.50 UT (11.50 pm EST on Nov. 18) 6 rev trail 51/hr
  • Nov. 19 05.59 UT (00.59 am EST on Nov. 19) 5 rev trail 28/hr
  • Nov. 19 10.23 UT (05.23 am EST on Nov. 19) 4 rev trail 5400/hr

According to Jenniskens, the 7-rev trail peak will last about .64 hours (about 38 minutes), the 6-rev trail peak about 4.1 hours, the 5-rev trail peak about 4.8 hours, and the 4-rev trail peak about .60 hours (about 36 minutes). More details are available at http://leonid.arc.nasa.gov/1998.html and predictions covering many cities around the world are posted at http://science.nasa.gov/headlines/y2002/09oct_leonidsforecast.htm? list519943

The team of Jeremie Vaubaillon and Francois Colas predict (in ZHR rates):

  • Nov. 19 04.04 UT (11.04 pm EST on Nov. 18) 7 rev trail 
    3400/hr with a range between 3100-3700/hr
  • Nov. 19 10.47 UT (05.47 am EST on Nov. 19) 4 rev trail 
    3000/hr with a range between 2700-3300/hr

According to Vaubaillon and Colas, the 7-rev peak will last about 2 hours, and the 4-rev peak about 3 hours, with a possible secondary peak. A basic description of how this was computed is found on their (updated) website at http://www.imcce.fr/s2p/leonides/predictions/Leonid_forecast.html

The team of Robert McNaught and David Asher predict (in ZHR rates), according to the article published in WGN 30-5 of October 2002:

  • Nov. 19 03.56 UT (10.56 pm EST on Nov. 18) 7 rev trail 
    1000/hr with a range between 810-2000/hr
  • Nov. 19 10.34 UT (05.34 am EST on Nov. 19) 4 rev trail 
    6000/hr with a range between 2900-6000/hr

According to McNaught and Asher, the 7-rev trail peak will last about 130 minutes (with a possible range of 105-150 minutes), and the 4-rev about 71 minutes. In their article, they mention that "the 4-rev dust trail... has had no close encounters with the Earth since it was formed... The situation is very different for the 7-rev trail... Numerous disruptions are caused by the Earth's passage close to the trail." They also comment on the brightness of the meteors that will be seen: "Despite the probably higher ZHR of the 4-rev trail in 2002, the lower <difference in semi-major axis between the ejected particle and the comet at the time of ejection> of the 7-rev trail... will result in a higher proportion of bright meteors. This will have a marked bearing on observed meteors for lower limiting magnitudes as would be expected in full moonlight."

McNaught and Asher, in their conclusion to the article in WGN, comment:

"Some uncertainty in the peak ZHR exists for both these trails that could increase the predictions by up to a factor of three. For the 7-rev trail over European longitudes the uncertainty results from the high ZHR from the same trail in 2001. Overall, it does not appear warranted to assume the observed activity of the non-linear encounter in 2001 should automatically imply higher than nominal rates in 2002, but without very extensive calculations we cannot deny this possibility. The 4-rev trail over N. American longitudes falls in roughly the same ZHR parameter space as the 1833 and 1966 Leonid storms. Given that both these storms seem rather underpredicted by our ZHR model, and bearing in mind that these are the only two linear encounters that are so badly predicted, it seems reasonable that the 4-rev encounter in 2002 could be double the nominal ZHR prediction."

So, how many meteors will we really see? It will be up to observers all around the globe to gather observations to find out! According to the researchers, in spite of all their efforts, we could still be in for some surprises. The International Meteor Organization, in their 2002 Meteor Shower Calendar, emphasizes that "other unexpected peaks are not excluded, so all observers should be alert right over the probable maximum dates, from November 16-20 especially."

As Jeremie Vaubaillon phrased it so well on the MeteorObs email list on September 10th:

"I think the important thing is to consider that, on next Nov. 19th, there will be a very strong Leonid shower, and perhaps the last you can see in your whole life (so strong I mean). So just remember to observe!"

Links to Leonids Web Sites

Leonid Peak Online Estimator: If you want to find out the estimated peak times for where you live, go to this site, and check out your location. At the bottom of the screen is a flux calculator. Pick the city closest to you and launch the calculator. It should give you a pretty good idea what the times will be for your area.

Thanks to Paul Greenhalgh of Vancouver, British Columbia, Canada, moderator of the Astronomy Clubs Around the World eGroup, for providing this information.

Ed Flaspoehler, Vice President
American Association of Amateur Astronomers
http://www.astromax.org

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