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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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