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THE ASTRONOMER Electronic Circular No 1458      1999 Oct 21 06.40UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074
INTERNET: GUY@TAHQ.DEMON.CO.UK             GMH at AST.STAR.RL.AC.UK
WORLD WIDE WEB                    http://www.demon.co.uk/astronomer
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POTENTIAL 'SURPRISE' METEOR SHOWER ON NOVEMBER 11?
Joe Rao (Skywayinc@aol.com) reports:
The recently discovered Comet LINEAR (C/1999J3) may serve to give
rise to a new meteor shower on November 11.
The circumstances concerning a prospective "Linearid" display on
the evening of November 11 is most intriguing.  The moment when
Earth passes closest to the ascending node of C/1999J3 at 2:41 p.m
EST/11:41 a.m. PST. Unfortunately -- daylight for North America,
although well into evening darkness over Europe.
The radiant for this prospective display very near to the star
Phecda, the lower left star in the bowl of the Big Dipper. From my
own calculations, I come up with an RA of 11h 40m, Dec. +53 deg.
So even for Europeans, the radiant stands only about a mere 5 degs
above the northern horizon (at latitude 40N) at the time that the
shower may reach its peak!
Nonetheless the separation between the Earth's orbit and that of
the parent comet is just over 0.011 a.u.  As to what type of
activity might be expected, it should be noted that the 1985
Giacobinids briefly produced an outburst of ZHR's of 600 to 800
from Japan, with the Earth following 21P/Giacobini-Zinner to its
node by just 26.5 days.  The separation between the orbit of the
comet and Earth was 0.033 -- or three times the separation between
the upcoming case of Earth and C/1999J3.
In 1933, when a major Giacobinid storm (ZHR = 3000 - 29000)
occurred, these values were 80 days and 0.005 a.u.  Earth is
following LINEAR to its ascending node by ~39.9 days.  Hence, the
situation regarding the prospective LINEARIDS is roughly midway
between the two above cases.
Among the chief differences between Giacobini-Zinner and LINEAR is
that Earth intersected comet debris on the inside of Comet G-Z's
orbit, whereas we would intersect debris on the outside of comet
LINEAR.  In addition, the dust-distribution surrounding LINEAR is
completely unknown. Also, Giacobini-Zinner is a well-known
short-period comet of 6.5 years and has been observed to circle the
Sun on many other occasions, whereas LINEAR is a newly discovered
long-period object of ~63,000 years.
I would strongly urge all observers to carefully monitor the skies
for possible meteors from this shower, especially during the
pre-dawn hours of November 11 (when the radiant is high up in the
northeast sky), as well as later that evening.  It appears that
should any significant outburst occur, those in western and central
Asia would have the best chance of viewing it (for them, in the
after-midnight/pre-dawn hours of November 12 local time).

Although we know that the Earth will be closest to the comet's
ascending node at ~19.6 UT on November 11, this doesn't mean that
the actual peak of a prospective LINEAR display could not occur
many hours earlier or later. An example of this occurred one year
ago with the 1998 Giacobinids: the time when Earth was predicted to
cross the node of 21P/Giaconini-Zinner was 20:53 UT on October 8;
but the shower actually reached its peak at 13:15 UT -- more than
7.5 hours earlier.
Thus, I would strongly suggest that all interested observers should
be on high-alert for a 24-hour interval on either side of the
predicted nodal crossing time of 19.6 UT/November 11.

Guy M Hurst