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Method of James Challis The method of J. Challis is based on two measurement of the same star and its movement only in the direction of the declination. Where in the sky The declination and the local hour angle can be chosen at will. Is the star trail in one of the directions small then choose a star which has a hour angle which differs about 90o. Alignment of the measurement filed and orientation of the axes The alignment of the measurement field is equatorial. The positive y-axis points towards the positive declination direction. Duration of the measurement The duration varies between 10 and 180 minutes. Zero point The zero point is the true celestial pole. After the alignment the hour axis has to be lifted by the value Rb towards the zenith. Procedure After the star has been centered it is time to track the star without any intervention. After about 30 minutes the position of the the star is read an the let the telescope track the same star for another 30 minutes and read the position a second time. Enter those two values into the fields Y10 direction and Y20 direction in units of the grid. Enter both measurement durations into seconds in First Observing period and Second Observing period. Enter into the field Resolution per unit the grid unit in arc seconds and hit submit. Example From the article Matrix Method for Coordinates Transformation by Toshimi Taki. With the following parameters Latitude:
52.1556 you obtain the following results Challis
lambda : 1716.61 arcsec
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Comments, questions, corrections: markus.wildi@one-arcsec.org |
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