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Re: (meteorobs) A-T 1996 ZAYGE ...long article

Wow!  This *is* an exciting discussion group.  We have controversy and
hard-hitting debate.  This is what science needs to make progress.
However, may I issue a word of caution based upon my 27 years of
involvement in meteor astronomy.  We should be wary not to slip into
personal attacks and hence debase the arguments.  It is all too easy
for this to happen---I've seen several occurrences---and they often
lead to long-term schisms that do meteor astronomy no good.  That's
enough of the sermon.

When I first learnt of the Triangulid meteors, I too was sceptical.
Since 1988 I'd made many telescopic observations during September but
hadn't noticed such a radiant.  Nevertheless, the next year (1994) I
set about looking for them.  Much to my surprise there did appear to
be a radiant around alpha Trianguli, albeit a weak one.  However, of
the five nights' observation where potential Triangulids were
recorded, if taken individually without the prior knowledge I have
would have only claimed one as showing a definite radiant.  This was
on Sep. 12/13 (lambda=170.1) with 13 out of 83 meteors coming from a
radiant at (30.5, +29), and there were 3 other possible candidates.
Sep. 10/11, with 7 of 68 being members of a possible Triangulid
radiant, would have been noted as a probable radiant for follow up
observations as 5 of the meteors intersected within a 0.5-degree
region.  There are more details in WGN 22:6, p.220--223.  Yes the
analysis was based data from virtually on one observer, and thus
should be treated with some caution.  I'd be the first to welcome more
telescopic observers to help investigate the existence of this radiant
(and numerous other possible radiants) in future years.

The interesting question is why have some experienced observers not
seen this shower yet others have.  My opinion is that there are a
number of possible factors.

1) The shower may be periodic.  Since I suggested this last year, Gary
Kronk seems to have accumulated more evidence to support such an
hypothesis.  I certainly was not surprised that there was minimal
activity in 1996.

2) The shower at "outburst" if it is periodic has a ZHR about 3, which
is barely detectable by visual methods.  There may be a bias by some
to detect the shower inflating the ZHR.  There have been experiments
where inexperienced observers were told the location of a fictitious
shower prior to a watch; they recorded many members of this shower. So
it is possible that the moderate contrast between George Zay's 1996
data and others who claim some A-T activity might have arisen in this
way, as well as chance alignments.  From what I've read, I think all
observers are claiming low or no activity.  Isn't that correct?

Given such a low peak ZHR and small-number Poisson statistics it is
not inconceivable that some observers will see a few per hour and
others none or virtually none during a short (say ~2-hour session).
Such minor showers need many visual observers plotting for many hours
to yield statistically meaningful results.

3) The shower seems to be rich in faint meteors.  Such meteors are
seen preferentially nearer the radiant.  At this time of year the
experienced observations have probably concentrated on the Aurigid
radiants so reducing their chance of seeing Triangulids.  Please
correct me if I am wrong, but wouldn't chance alignments due to the
increased plotting error at the A-T radiants also be larger if the
observer was facing say Camelopardus rather than Andromeda?

4) There are comparatively few observations made in September compared
with August or October, and bad weather during years of stronger
activity could easily be missed.  The luminosity function suggests
that good sky conditions are needed too.

5) Sporadic activity is at its highest and so a weak minor shower is
more easily lost in the noise if observers don't plot.

6) The telescopic shower I saw was different from the shower Gary and
George Gliba claimed to see in 1993 and 1994, and was due to chance
alignments and bias (recall the upsilon-Pegasids...).  This strikes me
as being a remarkable coincidence if it is true, especially as the
telescopic radiant has disappeared this year along with the visual
shower.

There is evidence for some showers which are predominantly observed as
telescopic meteors.  Upon careful investigation such "telescopic"
showers show some visual signal too, but it is much harder to detect.
Can't dispersive effects in older streams make the Earth pass through
only the part of the stream devoid of larger meteoroids?


We can't be dogmatic, just because of us haven't see the shower.  I
recall being told by an eminent UK amateur astronomer and populariser
that seeing stars fainter than +6 was impossible because he couldn't
see them!  If George Zay had made similar observations in 1994 as in
1996 we should have cause to be more sceptical about the shower's
level of activity or even its existence.  For me the weight of
evidence at present leans towards a periodic shower.

What's clear is that we should be alert for A-T activity in future
years and try to bring to bear all available methods to learn about
possible meteor radiants in this region.  I see video being
particularly important.

I agree with George Zay in that rigorous methods are needed to study
minor showers and a handful of meteors from a given region is not
proof of existence.  We've already had too many of those.  Unbiased
plotting over many years should show which apparent radiants are
artifacts and which are genuine.  On the other hand if you don't
advertise a few possible showers away from the majors, then you won't
have as many observers participating.  I guess that you need a bit of
both, and to be ruthless during analysis.

There are numerous other minor showers, which by their very nature are
difficult to demonstrate convincingly, but that shouldn't deter us from
trying.

Malcolm Currie
mjc@ast.star.rl.acdot uk
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