(meteorobs) Latest issue of eZine MeteorNews

Paul Roggemans paul.roggemans at gmail.com
Sat Aug 6 09:06:04 EDT 2016


I read the very interesting article of Joe Rao on page  48 and 49 of the
S&T magazine. I recommend reading this to anyone involved with meteor
observing.

I had observed some 'boring' Perseid displays since 1975, but in 1980 we
got totally surprised by a rich Perseid activity that displayed too many
meteors for our detailed plotting and data logging. We observed the first
time in the high Alps in Switzerland under much better circumstances that
we had at home and the ZHRs at maximum were about double of what we
had previous years. We were not the only observers impressed by the 1980
activity. In that time the theory was that the parent comet Swift-Tutle was
expected to be near its perihelion, but remained undetected. Was that true
and did we see enhanced activity related to such a theoretical parent body
passage through perihelion around 1980? When I met Brian Marsden I asked
him. He told me that the activity we saw in 1980 was very unlikely
connected to the Perseid parent body perihelion passage as according to him
the orbital period of comet Swift-Tuttle was longer than assumed and he
referred to his paper on this topic in the Astronomical Journal
published in 1973.

Observing the Perseids  under dark skies in 1988 from Southern France, I
had noticed a strange behaviour in the activity. I suspected statistical
random effects to account for my impressions, but when I  heard from many
other observers similar impressions, I got suspicious. What was going on? I
had been setting up and programming the IMO VMDB (Visual Meteor
DataBase) in June 1988 and the dataset of the 1988 Perseids was the first
new data entered into the VMDB to test the analyzing programs that I was
developing. The new analyzing tools developed as part of the VMDB revealed
a curious profile: a double peaked Perseid maximum. As I was still testing
and improving the VMDB programs I first considered all possible
explanations as if it could be an artifact caused by some mistake in the
analyzing methodology. But the method proved to be correct. Then, did Earth
cross a filament of dust in 1988 which caused this unexpected secondary
peak half day before the main 'historic' Perseid maximum? I wondered
if that new sharp peak that appeared on the ZHR profile could be the first
trace of the real return of the Perseids comet. The Perseids 1988 with
their double peaked maximum were the first result from the newly created
VMDB and some reactions were skeptical as the profile looked different than
expected. 1989  and 1990 produced a similar result but with less
observations available. A solid confirmation came when Japanese observers
witnessed a Perseid outburst in 1991 right at the solar longitude of the
peak that appeared as a new feature on the ZHR profile since 1988. The
outburst  reappeared in 1992 and the picture was complete when the Perseid
parent comet was rediscovered on 26 September 1992 by the Japanese amateur
astronomer Tsuruhiko Kiuchi.

Before the comet appeared its dust had given a hint of the return of its
parent comet. It was a great luck that this happened after I just created
the VMDB mid 1988, as it proved that it was useful to collect visual
observations on a global scale. It helped to promote the VMDB among visual
meteor observers worldwide. The idea of the VMDB was not new in 1988,
already in 1985 and 1986 attempts were made to collect, to store and to
analyze visual data from different groups around the globe. These first
analysis produced also some sub-maxima and peculiar shapes of ZHR activity
profiles, but suffered from a lack of a common methodology in observing and
reporting visual data. To solve this aspect I prepared a visual meteor
observing manual in English in 1986 which was published by Sky Publishing
Corporation. It helped to get compatible observing reports by the time the
'big' VMDB was created. The successful global analyzing reports generated
with the VMDB tools, proved to amateurs that it is worthwhile to pay
attention at some simple aspects required to be able to use observations
for some global analyzes. One of the most important, and still delicate
aspects is the limiting magnitude. This allows to compare different sky
circumstances and refers to the magnitude of a star that is just at the
limit of detectability and just not visible anymore. Hence the limiting
magnitude is not the faintest star you can see going over a sequence of
stars, but half way the magnitude of what you can still see and the nearest
magnitude of a star you fail to see. The problems with poorly determined
limiting magnitudes are well described in the global analyzes of the 2015
Perseids by veteran observer Koen Miskotte (see http://meteornews.org/
perseids-2015-global-analysis/).

Meanwhile computer models allow to predict where dust concentrations may be
expected, 2016 may produce enhanced activity. Is this the case or not? The
answer to this question depends on your observations in the next week!

Clear skies all!

Paul Roggemans (Belgium)

On Fri, Aug 5, 2016 at 3:10 PM, <Skywayinc at aol.com> wrote:

>
>
> In a message dated 8/5/2016 7:49:31 A.M. Eastern Daylight Time,
> paul.roggemans at gmail.com writes:
>
> To bring you in the mood for the rich Perseid return expected for 2016:
> Read the enthusiastic visual reports by Paul Jones and the global visual
> data analyses by Koen Miskotte and many more topics in the free eZine
> MeteorNews.
>
>
>
> I have not seen it mentioned on meteorobs (yet), but be sure to read my
> two-page feature article (on pages 48-49) on this year's Perseids in the
> August 2016 Sky & Telescope.
>
> -- joe rao
>
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