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(meteorobs) Re: 'Linearids'
I am sorry for many mistakes not only in grammer...
Michal Haltuf
Dne 20 Oct 99 v 7:45, napsal(a) Sirko Molau:
> ... a posting from Joe Rao on the 'meteorobs' mailing list.
>
> ---------- Forwarded message ----------
> Date: Tue, 19 Oct 1999 13:08:26 EDT
> From: Skywayinc@aol.com
> Reply-To: meteorobs@jovian.com
> To: meteorobs@jovian.com
> Subject: Re: (meteorobs) Radio observation + Linearids
>
> 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. 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 (not Beta Umi as earlier
> noted by Michal Haltuf). 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. (not 0.003 a.u. as noted by Haltuf).
> 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 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.
>
> 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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