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(meteorobs) Re: 1999 May 6/7 Eta Aquarids appear
My luck changed in the front yard on 1999 May 6/7 although it made me wait
until 2/3 of the session was done. I began at 428 EDT again with a sky
improved to LM5.5. Going for an Eta Aquarid rate of 0, there suddenly
appeared two of them at 520 just half a minute apart. Then another pair at
535, followed by 2 others before dawn. I stopped at 555 EDT. UT coverage
was 828 to 955 with 6 Eta Aquarids and no other meteors. Magnitudes in
order were 2,2,3,5,1,3. The brightest one was intense yellow with a
1-second train. I was pleased to see some shower member from this longitude
at last. It's been too cloudy since then but we need the rain that's
finally come ; been seriously dry for months.
On earth-grazing Etas, I generally don't see any until the radiant is
already 10 degrees up. It is typically 40 degrees long and lasting 2 or 3
seconds, and a train of similar duration is left. Then another half hour
goes by with just a handful of Etas, after which the rate increases rapidly.
That demonstrates how badly ZHR formulas fail at radiant elevations below 20
degrees. Stronger showers have a better chance of producing earth grazers
at elevations below 10 degrees just by sheer numbers.
One of the better earth grazers came last year on May 3/4 at 410 EDT. It
was an orange -1m going 50 degrees in 3 seconds, and the train was 2
seconds as judged by how long a couple of individual points along the path
lasted.
In 1981 I had a series of excellent May nights for Eta Aquarid observing
covering 1/2 to 12/13. In the final complete hour 426 - 526 EDT with skies
mostly LM7.0 - 7.3 I saw Eta rates 6,13,20,15,5,x,9,x,4,2,8,3. May 6/7 and
8/9 were missed. This was the last year I saw my highest rate on May 2/3
(it shifted to May 5/6 thereafter), plus the 20 seen was at the time my
best-ever Eta rate. Extremely high rates were being reported from Australia
during the early 80's. I can only conclude that a group of observers active
then had exceptionally high perception for meteors but it is a mystery how
anyone could have been seeing up to 100/hour when I was under 10/hr. If the
Eta Aquarids are really that strong, I should be seeing at least a
Perseid-strength display from here.
Norman
Norman W. McLeod III
Asst Visual Program Coordinator
American Meteor Society
Fort Myers, Florida
nmcleod@peganet.com
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