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Re: (meteorobs) Leonids in Australia

In a message dated 10/4/01 8:06:45 PM Eastern Daylight Time, 
rendrag@earthlinkdot net writes:

<<  I look up the date and time in my Royal Observer's Handbook of Canada and 
it says the second maximum is November 18, 18h UT.  That must be the 
Australian one. Now I would have no problem with this if Sydney were not on 
the other
side of the International Date Line, and that is one line that has
always confused me  8-).  Further it is about 10 hours ahead of
Greenwich and I'm used to being behind Greenwich.  I am assuming that
she will be in the vicinity of Sydney.  >>

    Actually . . . the maximum predicted for 18h UT on November 18 is the 
hour closest to the predicted convergence of two dust trails: one expelled 
from 55P/Tempel-Tuttle in 1699 and the other in 1866.  Based on the 
Asher/Lyytinen models, the projected peak encounter times between the two 
trails may be separated by as little as 12 (18:07 to 18:19 UT) to as much as 
53 minutes (17:31 to 18:24 UT).  This is an important factor regarding the 
view from eastern Australia.  

    And don't forget that because of their position relative to the 
International Date Line, this all is happening on Monday morning, November 19!

    In fact, for those located right along the immediate east coast (Sydney, 
Newcastle, Brisbane), morning twilight will have already begun as the trail 
expelled in 1699 is approaching its peak.  By the time the 1866 trail is 
reaching its maximum, civil twilight will have already begun, meaning that 
the sky will likely be too bright to see anything (barring an extremely 
brilliant fireball or bolide).  

    Those along the immediate west coast of Australia (Freemantle, Perth) 
will unfortunately have the Leonid radiant either just below or literally 
sitting on the horizon at the peak of the 1699 trail.  By the time the 1866 
trail reaches its peak the radiant will have climbed to about 10 degrees 
above the horizon.     

    The obvious compromise between low altitude versus morning twilight is to 
position yourself somewhere in the central part of Australia: the Northern 
Territory or South Australia.  Perhaps the very best locality in Australia is 
on the Cape York Peninsula . . . particularly Cape York itself, where the 
Leonid radiant will have climbed to ~40 degrees above the horizon by the time 
the 1866 trail attains its maximum.  Astronomical twilight will still be some 
minutes away, so the sky there will still be completely dark.

    By far, however, the most important consideration, are of course, the 
weather prospects.  In consulting my copy of "Global Distribution of Total 
Cloud Cover and Cloud Type Amounts Over Land" I find that that Western 
Australia has the lowest cloud cover amounts, with values as low as 23% for 
localities just to the south of the Hamersley Range.  Actually though, over 
much of Australia the cloud cover statistics appear quite promising . . . 
mostly in the 30 to 40% range.  

    The only localities where the cloud figures are above 50% are down along 
the coast of Victoria (including Melbourne): 60 to 65%, and also similar 
percentages 
for . . . you guessed it . . . the Cape York Peninsula!   

-- joe rao
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