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(meteorobs) News on the lunar Leonids
A summary of the six confirmed lunar impacts is given in the
table below. This is an ASCII plain text table that must be viewed
with a fixed-space font such as Courier for the columns to line up
properly. We are naming these with letters in the order of
discovery. The UT date is 1999 November 18. In each case, the
events were confirmed on my videotapes made at George Varros'
backyard in Mount Airy, Maryland, and the timings are from my tapes.
The previously-reported estimates of the locations of D and E were
rather far off in longitude, according to measurements of the video
images made by Ben Wun and me earlier today.
Accuracy, Approx. Discovered Selenographic
Name UTC sec. Mag1 Mag2 by Long. Lat. Description
h m s
F 3:05:44.2 0.6 5 9? David Palmer 69W 44N 50km e of Harding
D 3:49:40.40 0.03 3 7 David Palmer 69W 2N w. wall of Hevelius
E 4:08:04.1 0.6 5 8 David Palmer 77W 15S 120km SW of Rocca
A 4:46:15.2 0.1 3 8 Brian Cudnik 71W 14N 50km ENE of Cardanus
B 5:14:12.93 0.05 7 8 Pedro Sada 58W 15N 200km WNW of Marius
C 5:15:20.23 0.05 4 7 Pedro Sada 59W 21N 75km S Schiaparelli
Mag1 is the approximate magnitude of the flash estimated from my tape on
the half-frame on which it first appears. Mag2 is the estimated
magnitude a half-frame, or 1/60th second, later. In all cases
I can't see any evidence of the flash in the half-frame 1/30th second
after the first one, except for D, where it seems to appear there at
about 9th mag. The selenographic locations should be accurate to within
about 2 deg. or 50 km, but the locations of F and E could be in error
more due to foreshortening near the limb and lack of nearby features in the
Moon images generated with the Occult program used for the location
determination. Their locations can be improved by using a grid overlay
that we plan to generate. All of these are in the western part of Oceanus
Procellarum (Ocean of Storms) except D and E, which are in highlands area
a short distance west of the western shore of Oceanus Procellarum. The
times of B and C have been determined by Don Stockbauer, Victoria, Texas,
after creating an accurately time-inserted copy using an IOTA-Manly video
time inserter. He also determined the time of A, but for technical
reasons to less accuracy; it will be possible to refine it later. D, E,
and F have been timed from the tape just using a stopwatch.
D seems to be the brightest impact. Besides Palmer's and my
videotapes, it is also in videotapes by Pedro Sada and by Rick
Frankenberger in San Antonio, Texas. My image for the event also shows
three stars, from north to south (right to left in the image) being 7.6-
mag. SAO 146577, 8.2-mag. SAO 146578, and 8.9-mag. SAO 146574, all of
whose occultations were recorded a few minutes later. The first two stars
are also visible in David Palmer's frame of the D impact.
Sada reports two more events estimated at about 5th magnitude at
4:32:50.8 and 4:34:49.7 UTC, but they have not been found in other tapes
(the field of view of my 5-inch telescope used for the 6 known events was
aimed at a more southern part of the Moon than usual, so they would have
been missed if they occurred a little north of the equator). The 2nd
event was fairly close to the terminator. Other possible unconfirmed
events (some chance of their being videotape defects) were recorded by me
at 4:50:15.9 UTC and by David Palmer at 2:42:02.
The images for all six events are at http://iota.jhuapldot edu
That site also has a link to the article about the impacts that was
published on page 2B of the December 1st Baltimore Sun,
and the NASA news Web site that has an animation of impact A.
Some of Palmer's images are on the IOTA Web site at
http://www.lunar-occultations.com/iota
The mass of the impacting meteoroids, and the resulting craters, has
still not been resolved. Mass estimates range from 50 grams to 20 kg, and
crater sizes from several meters to almost 100 meters, in any case
probably too small to be visible from earth-based observations.
David Dunham, IOTA, 1999 December 3
Joan and David Dunham
7006 Megan Lane
Greenbelt, MD 20770
(301) 474-4722
dunham@erols.com
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