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Date: Tue, 19 Oct 1999 23:04:20 GMT From: Ron Baalke To: meteorobs@latrade.com Subject: (meteorobs) Potential 'Surprise' Meteor Shower on November 11? (forwarded) Sender: owner-meteorobs@jovian.com Reply-To: meteorobs@jovian.com

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

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