PREFACE

The Handbook for 1951 is the 43rd issue. During the past decade its circulation has increased from 1500 to 5500.

Four circular star maps 9 inches in diameter a t a price of one cent each, and a set of four maps plotted on equatorial co-ordinates a t a price of ten cents, are obtainable from the Director of University Extension, University of Toronto Toronto 5.

Celestial distances given herein are based on the standard value of 8".80 for the sun’s parallax, not on the more recent value 8".790 determined by Sir Harold Jones. Among the recent additions are:

1. Algol. Olin J. Eggen’s epoch 2432520.6303 and period 2.86731525d., as published in the Astrophysical Journal, 1948.
2. Sun-spots. A table of solar rotation numbers for observers of sun-spots, and an ephemeris for physical observations of the sun.

Mr. Charles E. Apgar, of Westfield, New Jersey, died on August 17th at the age of eighty-five. For a number of years this enthusiastic amateur astronomer had prepared the tables of Jupiter’s satellites for the Handbook. The editors regret the death of this loyal friend.

Dr. F. S. Hogg, the Assistant Editor, as in recent years, assumed the responsibility of preparing this volume and to him the chief credit of its success is due; but sincere thanks are tendered to all those whose names are mentioned in the book, especially to Miss Ruth J. Northcott and Professor J. F. Heard. Our deep indebtedness to the British Nautical Almanac and the American Ephemeris is thankfully acknowledged.

C.A. Chant.
David Dunlap Observatory,
Richmond Hill, Ont., November, 1950.