Smithsonian

Contributions to Astrophysics

VOLUME 4, NUMBER 1

CATALOG OF HOURLY METEOR RATES

by CHARLES P. OLIVIER

SMITHSONIAN INSTITUTION

Washington, D. C.

1960

Publications of the Astrophysical Observatory

This series, Smithsonian Contributions to Astrophysics, was inaugurated in 1956 to provide a proper communication for the results of research conducted at the Astrophysical Observatory of the Smithsonian Institution. Its purpose is the “increase and diffusion of knowledge” in the field of astrophysics, with particular emphasis on problems of the sun, the earth, and the solar system. Its pages are open to a limited number of papers by other investigators with whom we have common interests.

Another series is Annals of the Astrophysical Observatory. It was started in 1900 by the Observatory’s first director, Samuel P. Langley, and has been published about every 10 years since that date. These quarto volumes, some of which are still available, record the history of the Observatory’s researches and activities.

Many technical papers and volumes emanating from the Astrophysical Observatory have appeared in the Smithsonian Miscellaneous Collections. Among these are Smithsonian Physical Tables, Smithsonian Meteorological Tables, and World Weather Records.

Additional information concerning these publications may be secured from the Editorial and Publications Division, Smithsonian Institution, Washington, D. C.

FRED L. WHIPPLE, Director,

Astrophysical Observatory,

Smithsonian Institution.

Cambridge, Mass.

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Washington 25. D. C. - Price 15 cents

Contents of Volume 4

No. 1. Catalog of Hourly Meteor Rates, by Charles P. Olivier. Pages 1-14. Published June 6, 1960.

No. 2. Orbital Elements of Photographic Meteors, by Richard E. McCrosky and Annette Posen. Pages 15-84. Published May 1, 1961.

No. 3. Orbital Elements of Meteors, by Gerald S. Hawkins and Richard B. Southworth. Pages 85-95. Published March 23, 1961.

No. 4. Precision Orbits of 413 Photographic Meteors, by Luigi G. Jacchia and Fred L. Whipple. Pages 97-129. Published September 28, 1961.

No. 5. A Criterion for the Mode of Ablation of Stone Meteors, by Allan F. Cook. Pages 131-136. Published July 3, 1963.

No. 6. The Microscopic Properties of Meteorites, by Gustav Tschermak (Die Mikroskopische Beschaffenheit der Meteoriten, translated by John A. Wood and E. Mathilde Wood). Pages 137-239. Published June 4, 1964.

Contents

Publications of the Astrophysical Observatory

Catalog of Hourly Meteor Rates

Acknowledgments

References

Catalog of Hourly Meteor Rates

By CHARLES P. OLIVIER [1]

This catalog presents the average hourly rates of visual meteors for each night of the year, based on data for a period of 58 years, from 1901 to 1958 inclusive. About 60 percent of the data summarized here have appeared elsewhere (see References).

The catalog is based on observations received from hundreds of observers in many parts of the world. The contributors include members of the American Meteor Society, various persons who cooperated with the Society in reporting their own observations and those of others, and some workers who took part in the meteor program of the International Geophysical Year.

The table summarizes most of the observations received except for the following omissions:

(1) During the Perseid epoch, August 9 through 13, so many tens of thousands of meteors were reported, by so many observers, that some selection had to be made. Therefore, the relevant entries given in the table represent primarily the work of the more skilled observers.

(2) Similarly, in the 1930’s thousands of observations were received for the Leonid epoch, November 14 through 17; again the averages in the table are based primarily on the work of the more skilled observers.

(3) The table omits all observations of the great Draconid shower of 1946, October 9 and 10. Inclusion of these meteors would have resulted in completely misleading “averages” for those dates.

(4) In a few instances, an observer reported a rate from four to ten times what could be considered normal for the date and the prevailing atmospheric conditions. Correct or not, the reported number of meteors was so atypical that its inclusion would have given a false rate for that day in the average year. Such observations were omitted.

On the other hand, when high rates were obtained because a skilled observer was working in exceptionally good atmospheric conditions, such as often occur in a desert or semidesert, the observations were incorporated into the table.

The larger part of all the observations consisted of meteors that were either plotted or described. When plotting or describing a given meteor, an observer will miss any meteors appearing during the interval. Therefore, to obtain the true hourly rate of meteors that could have been observed during the period and in the prevailing atmospheric conditions, a correction was applied to the number of meteors reported. The correction is given in the following formula:

[1] Flower and Cook Observatory, University of Pennsylvania, Philadelphia.

where n_0 is the number of meteors that could have been observed had the observer been counting rather than plotting or describing them; n is the number of meteors actually observed; and p is the time taken to plot or describe each meteor; pn in the formula is expressed in minutes of time. The value of p is an estimate based on the author’s opinion of the skill of the particular observer. In applying the formula, the writer used tables giving the appropriate corrections for the various values of p; those values of p were set as 20, 30, 40, and 60 seconds.

Another correction is usually necessary because the number of meteors observed during a given hour depends to some extent on the conditions for seeing, and whether visibility was impaired by clouds, fog, moonlight, etc. In the following formula,

n_1 represents the average number of meteors that could have been counted by a skilled observer during that period under ideal conditions. The number of meteors actually observed usually represents only a percentage of the total observable under such conditions; the factor F represents the observer’s estimate of this percentage. Under ideal conditions, F was taken as 1.0; when F was 0.5 or less, the observations were considered very uncertain and were usually omitted; for the majority of reports used, the factor F was 0.7 or higher.

For a few observations, the author changed the estimated F when the data themselves obviously indicated that the original estimate had been in error. In most cases, however, the observer’s estimate of F was used.

The correction for time lost (formula 1) must always be applied before making the correction for visibility (formula 2). Otherwise, the hourly rate will be too high.

When the observer merely counted the meteors, no correction for time lost in plotting or describing was necessary, and therefore formula (1) was not used, although the correction for visibility conditions was still applied if the value of the factor F was less than 1.0.

Although no system of correction can give perfect results, nevertheless when one considers the inherent difficulties in seeing and recording all meteors that presumably appear in the observer’s field, one may conclude that the methods of correction given here yield a close approximation to the true rates.

Except for counts by observers working in ideal atmospheric conditions, the rates published in this table are of course higher (on the average by 25 percent) than the rates of meteors actually observed. In using the catalog, researchers must keep this fact in mind. In general, the figures represent the number of meteors that might have been counted by a skilled observer at a good station on a moonless, clear night when factor F equalled 1.0. Under conditions that fall short of this ideal in any way, the number of meteors actually observed will usually be smaller than the number given in the table.

An attempt was made to estimate the actual number of meteors that forms the basis of the table. A count of the tabulated figures for the 10th, the 20th, and the last day of each month totalled 36,000. We multiply this figure by 10.2 to obtain the total of the averages of all the days of the year. We then multiply by 0.8 to allow for the number of meteors added by the corrections supplied by formulas (1) and (2). These calculations give a total of about 294,000 meteors for the 58-year period. Probably no other catalog of meteor rates even approaches this total.

Acknowledgments

Without the hard work and active cooperation of many hundreds of observers, the data on which this table is based would not have been available, and the preparation of the catalog would have been impossible. Although we cannot name them individually, we wish to thank all those who contributed material. J. W. Simpson personally reported more than 17,000 meteors, and 35,000 more were sent in by observers he organized and encouraged. Prof. Mohammed A. R. Khan reported some 12,000, A. Pearlmutter some 10,000, C. E. Worley some 8,000, a group of observers in Whittier, Calif., about 20,000, and R. M. Dole over 10,000.

Two other groups, in particular, merit special mention. From Australia and New Zealand, R. A. McIntosh, M. Geddes, S. R. Fairbrother, and others contributed observations of about 10,000 meteors, approximately half of which were observed by McIntosh. The second group, at Tucson, Ariz., was organized by J. D. Williams and included R. Knabe, D. Brinegar, and T. Smith; this group reported more than 27,000 meteors, of which more than 17,000 were observed by Williams.

The preparation of this catalog, including the preliminary work involved, has occupied the author for nearly two years. I wish to express sincere appreciation to Mrs. Nora da Costa for her efficient help in making the table and to Dr. G. S. Hawkins of the Harvard Observatory and Prof. F. L. Whipple of the Smithsonian Astrophysical Observatory for their assistance in the publication of this data.

References

METEOR NOTES

1901–1950. Popular Astronomy, vols. 9-58.

1953–1956. Meteoritics, vol. 1.

OLIVIER, C. P.

1950. Some results from data secured by the American Meteor Society. Proc. Amer. Phil. Soc., vol. 94, pp. 327–335.

1957. Long enduring meteor trains and fireball orbits. Proc. Amer. Phil. Soc., vol. 101, pp. 296–315.

1958. Interim reports nos. 28, 29, and 35. Radio Meteor Research Program, Harvard College Observatory.

1959. Annual reports for 1956, 1957, 1958. American Meteor Society, Flower and Cook Observatory, Reprint 115, 20 pp.