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(meteorobs) Report from a meteor conference in Germany
Here are excerpts from a report I wrote about the annual meeting of
the German meteor group last weekend - also check out the complete
package at http://www.geocities.com/skyweek/mirror/182.html Story 3
with various sidebars:
New discoveries about the Leonids show amateur astronomy at its best
The systematic observation of meteors with the naked eye,
photographic and especially image-intensified video cameras has
become one of the rare fields in astronomy in which amateurs can not
only contribute to science - but where the science produced from the
amateur data can be crucial to advance the whole field. This has
become clear again at the annual meeting of the German Working
Group for Meteors (AKM) at the hospitable Sternwarte Radebeul on
March 17-19, where both new insights into the workings of the
Leonids were revealed but also the high state of 'routine' observations
these days.
Surprising fine structure in the ZHR
The main discoveries about the Leonids, as derived from a torrent of
data from the 1999 storm presented at Radebeul were:
There is an enormous fine structure in the activity profile,
i.e. the rate of meteors seen as a function of time, during the
hour-long storm - but it becomes evident only when one looks
at observations (visual and esp. by video) from specific locations
in the world. If one adds up the profiles from all places (Tenerife
to Jordan), the details average out. The video data from the
Jordan camp in particular reveal a strong 'early' peak of activity
around 1:45 UTC, 20 minutes before the sharp main peak, plus
enhanced activity around 2:30 UTC - all these features are
considered significant now. Confirmation by other (non-visual)
methods could be forthcoming.
Since observers at other sites (Spain was covered particularly
well) saw and recorded a rather different profile than Jordan or
France, it is even possible to generate a 'tomographic
picture' of the dust trail(s) that made the meteor rate explode.
The 1:45 UTC peak, e.g. was probably due to Earth's distant
encounter with a dust trail from Tempel-Tuttle's 1932
perihelion passage, though a significant effect on the meteor rate
had not been predicted. The main peak has resulted from the
1899 dust trail, of course, confirming brilliantly the model
calculations by D. Asher and R. McNaught.
Other surprises were the lack of faint meteors - video
cameras with better limiting magnitudes but smaller fields of
view saw far fewer meteors than those with worse sensitivity
but larger fields - and a possible breakdown of the
geometrical ZHR correction formula. Since decades the
influence of the elevation (h) of the radiant on the number of
meteors seen has been corrected geometrically into the Zenithal
Hourly Rate (ZHR), dividing the seen number of meteors by
sin(h). (Other corrections, such as for obstructions in the field of
view and the sky quality, apply as well.) The data from the 1999
Leonid storm cast a doubt on that simple formula: Those with a
low h got ZHRs of only 2000-3000 for the peak despite the
correction formula, while those with the highest h got 5000 as
the peak rate - it seems that the sin(h) effect must be replaced
by a (sin(h))**gamma correction, with gamma other than one.
Given the success of the Asher/McNaught approach in predicting the
time of the storm (a feat hailed by the IMO as equal in importance to
the basic understanding of how meteors work that came after the 1833
storm; Rendtel in WGN 28 [Feb. 2000] 1), there is great optimism now
that there will be even bigger storms in 2001 and 2002. The AKM
which had gone to Mongolia in 1998 and fielded teams to Tenerife and
Spain in 1999 has now started preparing two expeditions for 2001: One
will probably return to Mongolia (shudder!), the other go to Northern
Australia.
There is life beyond the meteor storms, too
Routine meteor observing can be a tough job, especially under bad sky
conditions and when no major meteor streams are active: Only a
handful of super-dedicated observers have spent more than 1000
hours gazing at the sky (with J|rgen Rendtel's breaking of the 4000
hour mark in 1999 an epic exception) - but video comes to the rescue.
The image-intensified video cameras have by now been automated to
such a degree that a couple of them watches the (mostly poor...)
German sky every night, feeding the signal directly into a PC where all
meteors are detected and logged.
Since not only numbers but also (very rough) brightness values, the
direction and angular speed are recorded, many advanced studies can
be done on the basis of these data - especially checking the reality of
'new' weak meteor streams that visual observers believe to have
discovered now and then. Thanks to such video coverage in January
and February 2000 its was possible, e.g., to dismiss the existence of the
'Xi Bootids' while discovering possible other radiants in that region of
the sky. Within 3 to 5 years there could be enough video cameras at
work that all meteor activity in the sky is monitored all the time and
from anywhere in the world.
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