GB595089A - Improvements in or relating to astronomical charts - Google Patents

Abstract

595,089. Astronomical charts. SUTER, H. April 16, 1945, No. 9466. Convention date, Sept. 2, 1944. [Class 146 (ii)] [Also in Group XIX] An astronomical chart comprises a flat disc 21 which, in addition to showing the stars divided by lines into fields, and to having lines 22, 23 representing the ecliptic and the celestial equator respectively, is provided with concentric margins containing a right-ascension scale 27, two date scales 25, 26, which in association with scale 27 can be used for reading the right ascension of the true and mean sun respectively, a band 24 showing the zodiac signs, a pointer 30 pivoted at the celestial pole and having declination graduations, and a transparent disc 32 rotatable about the celestial pole carrying a scale 35 of mean local time and showing horizon lines 33, 34 (with and without refraction correction), meridian line 36 and prime vertical 38 for the zenith point z. The R.A. of the true sun and the mean sun can be obtained from the scale 27 by setting the pointer 30 at the required dates on the scales 25, 26 respectively. The position of a planet can be obtained by the intersection of the pointer with the ecliptic when the pointer is set at the R.A. on scale 27 as obtained from the nautical almanac. To ascertain the visible part of the heavens as given by the horizon lines 33, 34, the disc 32 is rotated until the required time on the scale 35 coincides with the date on the scale 26. The position of the sun is given by the intersection of the pointer 30 with the ecliptic when the pointer is set at the particular date. Rising time of the sun, a planet or a star is obtained by rotating disc 32 until the east edge of the horizon line intersects the sun, planet or star when the scale 35 gives the time for any date on the scale 26. Similarly the times of setting and culmination can be obtained. The difference between readings on the scale 27 corresponding to the same date on the scales 25, 26 gives the equation of time. Sidereal time at any instant can be obtained, by setting the disc 32 with the mean local time of the instant on the scale 35 adjacent to the date on the scale 26, and observing the reading on the scale 27 corresponding to the meridian line on the disc. To ascertain mean local time, a star on the meridian is used. The disc 32 is set with the meridian line on the star and the time reading obtained on the scale 35 opposite to the particular date on the scale 26. In the case of the Sidereal time and mean local time readings, a subsequent correction is necessary because the date reading corresponds to the midnight hour.