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(meteorobs) More on the LINEARIDS

Some additional comments about a prospective meteor display from comet LINEAR 
(C/1999J3):

1) On November 11, we will be arriving at the comet's DESCENDING node, not 
ascending (as originally stated).

2)  The comet in question (LINEAR or C/1999J3) is a long-period comet.  It's 
orbital eccentricity is estimated at 0.999366 giving it an estimated period 
of 60,475 years.  As such it is not a "new" or "virgin" comet in the Oort 
sense and may very well have been here before in the far-distant past.  

    There unfortunately has never been a recorded case of any truly historic 
meteor showers emanating from a comet of such a long period as this.  Most of 
the comets that have given rise to spectacular meteor outbursts are of the 
short-period variety (Tempel-Tuttle, Giacobini-Zinner, Biela, Pons-Winnecke). 
 The Perseids are related to Comet Swift-Tuttle, whose period is roughly 130 
years.  Perhaps the most extreme case for a long-period comet are the Lyrids, 
which have produced occasional, unpredictable outbursts of activity (such as 
1982 and 1803, the latter case producing many hundreds of meteors per hour).  
The Lyrids are associated with Thatcher's Comet of 1861 whose period is 
approximately 415 years.

3) The prospective LINEARID radiant position was originally given as R.A 
.11h40m  Dec +53 degrees. Which would place it within a few degrees of the 
star Phecda (Delta Ursae Majoris).  This position was recently called into 
question by meteorobs member Chrystian Steyaert, who independentally obtained 
a position of R.A. = 7h20m, Dec = -40 deg.  However, once it was realized 
that the nodal crossing point was descending and not ascending (see #1 
above), he later wrote:  "After correction, my results agree fully with 
yours!"  Steyaert also added that:  "( I ) don't recall if you gave a 
velocity, but the 57 km/s is certainly a bonus for the radio observations."  

4) While I commented that prospective observers should be on high alert 
within 24 hours either side of the predicted nodal crossing, I have since 
done some research into other comets that have produced brief meteoric 
outbursts.  

The "Bootids" or Pons Winnecke Meteors provided a very sharp and unexpected 
outburst on June 28, 1916, observed by the British Observer William F. 
Denning.
Interestingly, the parent comet passed through its nodal crossing point on 
September 8 of the previous year.  The comet's orbit at the node was 0.043 
a.u. sunward from that of the Earth.  More interestingly, the outburst 
observed by Denning came nearly three days before the Earth reached the node!

Similarly, another Bootid/Pons Winnecke outburst occurred on June 27.21 (UT), 
1927 and was observed by both Russian and Japanese observers.  On this 
occasion, at the nodal crossing point, the parent comet was 0.028 a.u. 
outside of Earth's orbit.  Earth would arrive at the node only 2 days befind 
the comet -- yet maximum activity again came about three days before the 
Earth reached the node.

Biela's Comet (which of course, no longer exists), apparently was the cause 
of large numbers of meteors and occasional bright fireballs from Andromeda 
which were observed on December 7, 1830 (from France) and on December 7, 1838 
(Connecticut).  What makes these observations interesting is that although 
the orbits of Earth and Biela very nearly coincided at the nodal crossing 
point, the 1830 observation came nearly two years before Biela's arrival at 
the node and the 1838 observation occurred about seven months before Biela 
reached the node.  In addition, the 1830 and 1838 "Bielid" nodal crossing 
points corresponded to the November 30 point in our orbit -- yet, as noted 
above, the two above displays were noted a full week later!     

Which, put simply, means that we should not have tunnel-vision and 
concentrate solely on the afforementioned nodal crossing time for the 
supposed LINEARIDS of November 11.82 UT, but be on the lookout for any 
unusual prospective activity perhaps a week before to a week after this time 
(~November 4-18).  This, of course, means a potential cross-over with both 
the northern and southern Taurid shower branches which peak in the first week 
of November, as well as the long-awaited arrival of the Leonids on November 
17-18.  In a recent exchange of e-mails on this subject, Dr. Brian G. Marsden 
of the Central Bureau for Astronomical Telegrams noted that: "I'm skeptical 
about meteors like this from a long-period comet, but I
suppose one never knows."  

Indeed, as noted above, a significant or noteworthy meteor display from a 
long-period object such as C/1999J3 is quite unprecedented.  Absolutely 
nothing may come of it.  But, on the other hand . . . you never can tell!

-- joe rao   
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