Tiedote meteorobs listalta
Date: Tue, 19 Oct 1999 23:04:20 GMT
From: Ron Baalke
Subject: (meteorobs) Potential 'Surprise' Meteor Shower on November 11?
Forwarded from Joe Rao (Skywayinc@aol.com)
Subject: Potential "Surprise" Meteor Shower on November 11?
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 11th 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-degrees 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.
Nonetheless . . . 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. more
than 7.5 hours earlier.
Who knows? It might prove to be an interesting warm-up for the Leonids,
which are due to peak just a week later!
-- joe rao