File:Astronomy. Determination of time, longitude, latitude, and azimuth (1913) (14781247212).jpg

Identifier: astronomydetermi00usco (find matches)
Title: Astronomy. Determination of time, longitude, latitude, and azimuth
Year: 1913 (1910s)
Authors: U.S. Coast and Geodetic Survey Bowie, William
Subjects: Spherical astronomy
Publisher: Washington, U.S. Govt. print. off.
Contributing Library: Wellesley College Library
Digitizing Sponsor: Boston Library Consortium Member Libraries

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rs are as follows: A is plus except for stars between the zenith and the pole. B is plus except for stars observed at lower culmination. O is plus for stars at upper culmination and minus for stars at lower culmination, whenobservations are made with the instrument in the position, band (clamp or illumination) west. Cis minus for stars at upper culmination and plus for stars at lower culmination when obser-vations are made with the instrument in the position, band (clamp or illumination) east. These factors are given to two decimal places in the tables on pages 62 to 77, and will befound sufficiently accurate whenever the errors of adjustment, a, b, and c, are not allowed toexceed one second of time. In 1874 this Survey published more extended tables, giving thesefactors to three decimal places. Where, from any cause, observations are made with an instru-mental error abnormally large it is desirable to take the corresponding star factors from themore extended table or to compute them.
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DETERMINATION OF TIME. 61 STAR FACTORS OBTAINED GRAPHICALLY. For a number of years there has been in use in the Survey a nomogram for obtaining graph-ically the star factors A, B, and C, and also k, the correction for diurnal aberration. Thisnomogram was devised by Mr. C. R. Duvall, a computer in the Survey. It is not only moreexpeditious than the tables, but the elimination of the double interpolation which the use ofthe tables necessitates adds to the accuracy of the derived factor in many cases. The nomogram is shown in illustration No. 9, reduced in size. It consists of two systemsof equidistant parallel lines perpendicular to each other, a system of arcs of equidistant concen-tric circles, and a transparent arm, carrying a graduated straight line which revolves about thecommon center of the circles. The decimeter has been the unit of length in the nomogramsused. The three systems of lines are drawn at a common distance apart of 1 centimeter. Theestimated tenth of this centimeter

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