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Re: (meteorobs) A-T 1996 ZAYGE ...long article
Interesting last comment, Malcolm. In examining my Perseid data, I get the
feeling I was too restrictive on the Perseids, i.e. some were classified as
Sporadics. I'm inexperienced but picky I guess. Wayne
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Original Text
From: Malcolm Currie <mjc@astro1.bnsc.rl.acdot uk>, on 9/19/96 1:03 PM:
To: <meteorobs@latradedot com>
MJC>> The shower at "outburst" if it is periodic has a ZHR about 3, which
MJC>> is barely detectable by visual methods. There may be a bias by some
MJC>> to detect the shower inflating the ZHR.
GWG> On the first point, I believe that a ZHR of 3 is too low by a few
meteors.
GWG> When Gary Kronk and I independently saw the A-T meteors Sept. 11/12
1993,
GWG> I saw about 5 or 6 per/hr. There was no bias then because I didn't
expect
GWG> anything from that area, as I was watching for Southern Piscids.
I was taking an average of 1993 and 1994 and including other observers
to get a ballpark figure to make my point. ZHR=3 is regarded as the
practical borderline for visual measurement. An increase of 1 in the
ZHR doesn't invalidate the difficulty of observing such showers.
Certainly a ZHR=4 shower will on average be easier to detect than a
ZHR=3 shower, but that's only a comparative statement. Also I was
careful to write "about 3". From your 1993 data, the one-standard
deviation error is going to be about 30 per cent even if we ignore any
systematic effects and correction for chance alignments. 6+/-2 is
still compatible with "about 3".
GWG> The next year, observing on Sept. 10/11, and 11/12, for 5.00 TeFF, I
saw
GWG> about 4 A-T meteors per/hr. However, I may have had some bias, but
doubt
GWG> if it allowed inflation of the ZHR by more than 1 per/hr.
That's still about a 25-per-cent formal error. I don't know what your
perception coefficient and lm values (in both years) were, but say the
ZHR was 4, the error is going to be about 1. Even if the ZHR was 5,
it's less than two standard deviations different, and so statistically
the values aren't different. If what you are implying is that it is
unlikely that all 11 alleged shower members in 1993 and the ~20 in
1994 were due to bias or chance alignments, I would have to agree.
GWG> As for this year, I only saw 6 possible A-T meteors in 4.00 TeFF. Not
GWG> enough to verify any activity.
True but the shower could still be present at a weak level if some of the
particles have spread around the orbit.
GWG> As to the possibility of bias by some to detect the shower inflating
GWG> the ZHR, I agree that this is a real problem when ZHR is low, as it
GWG> was this year.
Are you implying that it doesn't affect a ZHR=4 shower too? Here's a
more extreme example: in my experience, especially with novice or
occasional observers, the number of sporadics per hour drops during
the Perseid maximum. Many sporadics appear to be misclassified as
Perseids. Yes the percentage difference is more marked for a ZHR=1
than a ZHR=4 shower.
Malcolm Currie
mjc@ast.star.rl.acdot uk