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Re: (meteorobs) "Mr. Denning"
During the 19th century, a number of radiant catalogs of varying value were
published. The true nature of meteor streams was debated until the early
20th century, and so there was a great deal of variation in the methodology
of meteor radiant work. Meteorics was a young science, and basic questions
were still being answered.
The behavior of streams and radiants was one of those questions. That
radiants moved from night to night was not generally known; as late as 1924
Dr. C. P. Olivier, in his seminal work "Meteors", devoted 30 pages and 2
chapters to arguing against the existence of stationary radiants. Knowing,
as we do, that radiants move from night to night, it is apparent that the
best definition of a radiant is obtained by observations done on a single
night. Some of the early catalogs used meteors observed as much as 30 days
apart to define a radiant, but with our 20-20 hindsight, we can see that
this would not work at all.
The first work that gave a list of radiants mostly observed on one night was
Schiaparelli's list of 189 radiants published in 1871. Here's the important
point to remember concerning this list (and radiant catalogs in general), as
pointed out by Schiaparelli himself: in several cases, the same radiant
appears on another night, in a slightly different position, and so his list
represents 189 observed radiant positions, not 189 separate streams.
Others continued to publish lists of radiants based on combined observations
over many nights. Captain G. L. Tupman, however, published a list of 102
radiants based on his observation of 3800 meteors in 1869-71. Most of
Tupman's radiants were observed in a single night; the eastward progression
of the Perseid radiant is readily seen from his radiant observations.
Again, the important point is that his catalog represents 102 radiants
observed, not 102 separate streams.
Denning's great work appeared in 1899 in the Memoirs of the Royal
Astronomical Society under the title "General Catalog of the Radiant Points
of Meteoric Showers and of Fireballs and Shooting Stars observed at more
than one Station". His catalog contains 4367 radiants which differ in
greatly in accuracy because he included everything he could find records of,
regardless of method. In his own work, he was inclined to combine
observations made on several nights to determine a radiant.
In the early 20th century, Dr. C. P. Olivier campaigned against the practice
of combining observations made over many nights to produce "radiants". He
produced three major works in 1911-1920 in which he determined over 1200
radiants from his own observations and observations by American Meteor
Society members, using a more disciminatory approach. In 1917, the Meteor
Committee of the American Astronomical Society, which Olivier chaired,
produced a document detailing the scientific requirements for radiant
determination. Norm McLeod's "Suggestions for Visual Meteor Observing"
includes a page that captures much of what the AAS report mentions:
http://www.amsmeteors.org/mcleod/mcleod6.html.
The AMS records now include over 7000 radiants. The point to again
emphasize is that this represents 7000+ individual radiant observations of
various streams, some of which may be nondescript. It does not represent
7000+ different streams, and this is true for Denning's list and the
catalogs of others.
Jim Bedient
-----Original Message-----
From: George W. Kelley, Jr. <stargazer@naxs.com>
To: 'meteorobs@jovian.com' <meteorobs@jovian.com>
Date: Friday, May 14, 1999 1:02 PM
Subject: RE: (meteorobs) "Mr. Denning"
>Robert McNaught et al:
>
>Now that Michael's questions about sporadic meteors have been answered
>well, I wish to pose an obliquely related question.
>
>It seems to me that meteor observers in the 19th century might have
>considered the projected intersection point of any two sporadic meteors
>observed the same night as a real shower radiant. As evidence of this, I
>point you to this book:
>
> Celestial Objects For Common Telescopes
> by The Rev. T. W. Webb
> (edited and revised by Margaret W. Mayall)
> Dover Publications, NY, 1962
>
>On pages 247 and 248 of the book, the Rev. Webb presented a list of meteor
>shower radiants that he considered the best of those published by one Mr.
>Denning. Of course, the list includes the currently recognized strong
>showers and lots of minor ones.
>
>What is so intriguing to me about this list is the first column, headed
>"Ref. No. D.," or, I surmise, Mr. Denning's reference numbers: The last
>shower listed has in this column the number "905;" i.e., Mr. Denning's list
>contains at least 905 possible radiants! How about that!
>
>Does anyone have any information about Mr. Denning and his list that they
>can share with us?
>
>George Kelley
>
>
>
>
>
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