Dear Listees, especially those staying up for the midnight crescendo of an
average Leonid meteor shower this Saturday evening - Sunday morning:
http://leonid.arc.nasa.gov/estimator.html
"Most visible Leonids are between 1 mm and 1 cm in diameter. For example, a
Leonid meteor of magnitude +5, which is barely visible with the naked eye in
a dark sky, is caused by a meteoroid of 0.5 mm in diameter and weights only
0.00006 gram."*
"Persistent train/Ursa Major on left" :
http://leonids.hq.nasa.gov/leonids/gallery/files/195.html
That is intended to be the threshold limit of visible Leonids, indicating
others can be much havier. Extrapolating this asumptions of the 0.00006
gram meteoroid, once can calculate that a -7 magnitude (minus seven = around
twice Venus) bright fireball would weigh in at 3 grams, though the high
speed of the Leonids makes it unlikely anything of that size could make it
to the ground without a major high altitude KA-BOOM. This agrees very
nicely with Beech M. and and L. Foschini, "Leonid electrophonic bursters",
A&A 367, 1056-1060 (2001), where it is mentioned that 100 gram fragments are
suspected to reside in the Leonid meteoroid stream. Their reference for
that defers to Bellot-Rubio, Ortiz and Sada (2000) and Spurney et. al
(2000). Yes, the same Ortiz that Brown-Ortiz tiff.
.
The average height of the end of the luminescent path of bright Leonids is
estimated at 80 km. So the gap is awefully large...
Best wishes,
Doug
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