Re: (meteorobs) A rethinking of the upcoming Leonid meteor rates
> Those who have read my Leonid paper in WGN 27:3/4 will have noted how
>through orbital simulations I had integrated material from the great Leonid
>storm in 1833 forward to 1866. What I discovered was that the orbital
>separation between the Earth's orbit and this 1833 material had widened to
>almost 0.007 a.u. by 1866. Also, I integrated material from the 1966 forward
>to 1999 and found a separation between Earth's orbit and this material of
>nearly 0.003 a.u.
> My initial supposition was that such a difference between 1866 and 1999
>would result in 1999 seeing much higher hourly rates compared to the 6000 to
>10,000 rates of 1866 (as noted in Icarus 138, 287-308 by Peter Brown).
> Last week however, I had a chance to e-mail David Asher and inquire why
>he left out the meteor trail map for 1866 from the Armagh Observatory
>internet site. He kindly -- and very quickly -- responded by adding the map
>to the site, which indicated that a meteor trail shed by 55P/Tempel-Tuttle in
>1733 was primarily responsible for the 1866 display. Over this past weekend,
>I performed an integration for 1733 myself and found that this material
>passed ~0.001 to 0.002 a.u. from Earth's orbit in 1866, pretty much
>confirming what David had indicated.
> As a result of this, I am toning-down my original "guesstimate" of Leonid
>activity to 2,000 to 6,000 per hour. In WGN 27:2, David and Rob McNaught
>suggest a peak of 1,500 per hour -- a rate that is quite close to the
>lower-end of my revised range.
> I should, however, point out something that is not-often cited in
>predicting Leonid rates and that is the propensity of meteor activity during
>a storm apparently coming in "waves" or "surges." The oft-quoted "40 meteors
>per second" from Dennis Milon's team at Kitt Peak Observatory in 1966 was
>arrived at after a consensus, but was probably the ABSOLUTE UPPERMOST LIMIT
>of observed activity. Indeed, there were others who claimed to have seen
>similar, if not even higher rates (James Young at Table Mountain Observatory
>suggested 50 per second!) but again, this may have only been an extreme upper
>limit. As I comment in a footnote in my WGN paper, many other witnesses of
>the 1966 storm noted lower rates of "only" 10 to 30 per second. A very
>telling description came from Dana K. Bailey of Boulder, Colorado, who
>commented in the January 1967 Sky & Telescope that " . . . no fewer than 10
>new meteors were appearing each second, for many minutes, yet sometimes the
>rate was double or triple that . . . "
> Another suggestion of meteor activity apparently coming in surges, comes
>from a description of the 1866 Leonids as reported in The London Times:
>"The spectator had soon counted half a dozen; then he felt sure he had seen
>thirty; then six or seven in a minute . . . Then there came two or three
>together; then not less than a dozen of all kinds."
> In essence . . . if indeed, a maximum of 1,500 per hour occurs this year,
>that's 25 per minute or one meteor every two or three seconds. It would not
>be surprising however, if -- based on the above description -- there come
>brief intervals when the rates may actually reach several times this rate.
>You've heard of major storms that, for example, produced " . . . sustained
>winds of 50 miles per hour, but with occasional gusts to 80." Well . . . in
>1999, it could very well be that we'll hear of overall sustained
>single-observer rates of say, 2,000 per hour with occasional bursts ("gusts")
>-- joe rao
>To UNSUBSCRIBE from the 'meteorobs' email list, use the Web form at:
Norman W. McLeod III
American Meteor Society
Fort Myers, Florida
To UNSUBSCRIBE from the 'meteorobs' email list, use the Web form at: