view Abstract Citations (5) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A new determination of the lunar parallax. O'Keefe, John A. Abstract The lunar parallax has been measured by determining by photoelectric measurements the times of occultation of the same star at several widely separated points in the United States. The essential tool not used in previous determinations of the lunar parallax is the geodetic triangulation of the United States, which appears to be accurate to I part in 200,000 on individual loops. It is a further consequence of the use of geodetic triangulation that what is determined is the moon's distance, rather than its parallax; consequently it is not necessary to make an assumption about the earth's radius in order to convert the results to kilometers. The technique is to place the observers along the line covered by the shadow of a chosen lunar feature. With a I ~-inch Cassegrain reflector feeding into a 1P21 photocell and thence to a Brush Recorder, which also records the time signals emitted by WWV, the observers measure the instant of occultation. In the computation, the results are substituted into the following equation: = JAN + 6A~ + c~Aa + dA~ + JAir +JAk + gAff One equation of this kind is formed for each station. The quantities AN, Ab and AH can be set equal to zero, since the U. S. triangulation, after transfer to the Hayford ellipsoid, is essentially error-free. The quantities C, and d, and J are the same at both (or all three) stations, since they depend on the star's declination and the position angle of the contact, which do not change. The quantities Aa, A~ and Ak, error of the moon S radius, are also the same at all stations; consequently these terms drop out in forming the differences. Thus the correction to the parallax becomes, for two stations, S1, and 52, Air = A~1 - A~2 e1 - e1 The value found was Air = -o.056~0.033. The errors arise largely from the libration of the moon during the time of the observation, and cannot be estimated with any degree of preclslon. The residuals Aff at individual stations indicated an error of 0'I0052 for an individual observation. The resulting value of the moon's distance is: 384,410 international kilometers, an increase of about 6 kilometers from Brown S value. This value is to be regarded as preliminary, since it may be possible to correct it when the librations can be taken into account, as, for example, by the aid of the new tables under construction at the Naval Observatory. A byproduct of the investigation is the discovery that the star 228 B Aurigae, No. 996 of the Zodiacal Catalog, is double. The separation is 0' 53 resolved along a position angle of 2550 53'; the other component of the separation is unknown. The difference in brightness between the components is 0.5 mag. It will be possible to observe this star again in the spring of 1951, and it is hoped that observers with photocell equipment will get it. The instrumental equipment for this observation was designed by Mr. D. D. Mears, under the supervision of Prof. A. E. Whitford, of the University of Wisconsin. Mr. Mears also supervised the field parties. The office computations were performed under the supervision of Miss Nora B. Moser. The work was done under the general supervision of Mr. F. W. Hough, Chief, Geodetic Division, Army Map Service. Thanks are due to the Commanding Officers of the Army Map Service, Col. W. H. Mills and Col. John G. Ladd, for their kind interest and support of the program, and to the Naval Observatory for much technical advice and assistance. Army Map Service, Washington, D. C. Publication: The Astronomical Journal Pub Date: 1950 DOI: 10.1086/106453 Bibcode: 1950AJ.....55R.177O full text sources ADS |