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The Leonid Meteor Shower: Historical Visual Observations
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Short Description: Leonid meteor shower by radar, visual and video techniques, Mon. Not. R. Astron. Soc. 300, 244–250. Burke, J. G. 1986. Cosmic Debris: Meteorites in History. ...
Content Inside: Icarus 138, 287308 (1999) Article ID icar.1998.6074, available online at http://www.idealibrary.com on
The Leonid Meteor Shower: Historical Visual Observations
P. Brown
Department of Physics and Astronomy, University of Western Ontario, London, Ontario, N6A 3K7, Canada E-mail: peter@danlon.physics.uwo.ca Received July 20, 1998; revised December 10, 1998
The original visual accounts of the Leonids from 1799 to 1997 are examined and the times and magnitude of peak activity are established for 32 Leonid returns during this two-century interval. Previous secondary accounts of many of these returns are shown to differ from the information contained in the original accounts due to misinterpretations, typographical errors, and unsupported assumptions. The strongest Leonid storms are shown to follow a Gaussian activity profile and to occur after the perihelion passage and nodal longitude of 55P/TempelTuttle. The relationship between the Gaussian width of the strongest returns and their peak activity is established, and the particle density/stream width relationship is found to compare favorably to that expected based on observations of IRAS cometary dust trails. Variations in the width of the 1966 storm as a function of meteoroid mass are shown to be consistent with that expected from classical gas-drag meteoroid ejection treatments. The five largest storms from 1799 to 1966 are found to peak at solar longitudes systematically larger than 55P/Tempel Tuttle's nodal longitude at the same epochs, suggesting an asymmetry in the dust ejection perpendicular to the cometary orbital plane. The dust-distribution about 55P/TempelTuttle is reevaluated with these new data and predictions are made for the 19992000 showers. c 1999 Academic Press Key Words: meteors; Leonids; visual observations.
1. INTRODUCTION
Meteor Science in its modern form was born on the morning of November 13, 1833. It was the great Leonid return of that year which provoked widespread interest in the subject after being observed extensively in North America (Olmsted 1834). Due to its unique nature of producing strong showers every 33 years, the Leonid shower is probably the most extensively written-about meteor stream. This observational data base permits useful constraints to be placed on modern theories of the stream's evolution. Detailed histories of the shower can be found in Yeomans (1991), Mason (1995), Dick (1998), Burke (1986), and Littman (1998). With the recent passage of TempelTuttle through perihelion, activity from the shower is again on the rise as is interest in the stream in general. Our motivation is to reexamine as many original accounts of the shower which contain usable numerical information as possible and to determine the characteristics
of past showers, independent of the many secondary accounts which appear in the literature, in an effort to better understand the stream's past activity, its formation, and as a way to predict what may happen in the years from 1999 onwards. In addition, this revised set of historical Leonid data provides a set of observations reduced in a common manner, which any model of the stream must be able to explain and to which others can easily examine and apply their own corrections. In this work, we examine in detail available original records of the Leonids for modern returns of the shower (here defined to be post-1799). In doing so, we attempt to establish the characteristics near the peak activity of the stream borne out by the original records for years near the passage of 55P/Tempel Tuttle. We utilize firsthand and original records of the shower for each year to construct activity curves for the shower. Using these data we then estimate the solar longitudes for each return for which significant activity occurred and the approximate time of peak activity. The method of reduction of these visual data and the methodology of their interpretation is given in Section 2. In Section 3 we present the results of application of these reduction techniques to available original visual observations of the shower from 1799 to 1997, along with discussions of the limitations and biases inherent in the reduced activity profiles for each Leonid return examined. Section 4 presents some discussion of the results in the context of the dust distribution about 55P/ TempelTuttle and implications for the Leonid shower in general based on the reinterpretation of these observations. A summary of the primary conclusions from this work is given in Section 5.
2. OBSERVATIONS OF THE LEONIDS
In what follows we present a detailed, though by no means complete, examination of the original accounts associated with the Leonids between 1799 and 1997. The original sources which were consulted to form the activity profile for each year are given in the figure captions. A brief discussion of each year's activity profile is given and mention made of previous errors found in secondary sources. Years which are not discussed are specifically omitted due to a lack of access to the original observational material. Leonid activity reported in historical literature is based on visual observations of the shower. From the hundreds of
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0019-1035/99 $30.00 Copyright c 1999 by Academic Press All rights of reproduction in any form reserved.
