4. EXAMPLE: March 17, 1902. Longitude by account 67° 30′ W. Latitude by account 40° 16′ N. The observed altitude of the sun's lower limb was 48° 04′ 10′′ S. Time by chronometer 4h 59m 078 P. M., and fast 10m 10s. Height of eye 39 feet. correction-4′ 30′′. Chro. time Fast G. M. T. Cor. equa. time Find the latitude. Index 4h 59m 078 P. M. Equa. of time N. A. 8m 438. 12 G. A. T. Long.67° 30'W.= =-4 30 00 G. M. T. 4h 48m 57s Hour angle IO 17 3.47 8 39.65 08.723 = X 4.8 5784 2892 Square of hour angle (10m 17s) = 10m.3 X 10.3 = 106 5. EXAMPLE: January 26, 1902, A. M. The observed meridian altitude of the moon's lower limb was 59° 16' 20" S. Longitude by account 37° 30′ W. Height of eye 35 feet. Index correction +4' 05". Find the latitude. Moon's mer. pass. 25th N. A. 13h 51m.8 H. D. pass. N. A. 2m.06 1030 412 16 26.9 Cor. for long. 5. 1=5m.150 ridian altitude of the moon's lower limb was 49° 53' 30" N. Longitude 75° 00' E. Height of eye 30 feet. Index correction -3' 20". Find the latitude. Moon's mer. pass. N. A. 11h 04.9 H. D. mer. pass. N. A. 2m.39 Obs. alt. L. L. 49° 53′ 30′′N. Dec. at 6h N. A. 13° 07′ 48′′.7 N. 6, 4. 26 14 16 S. EXAMPLE: March 17, 1902. The observed altitude of the Pole Star was 38° 30'. Longitude by account 53° 30′ W. Local mean time 6h 57m P. M. Height of eye 26 feet. Index correction +2' 10". Find the latitude. Hour angle 5 11m 50s = 77° 57' 30" log. cosine 9.31937 table 44 Star's pol. dist. in miles 72′.9 log. 1.86273 13g. I.I82Io 42 42 6, 4. EXAMPLE: October 3, 1902. The observed altitude of the Pole Star was 22° 33′ 00′′. Local apparent time 5h 30m A. M. Longitude by account 63° 00' E. Height of eye 35 feet. Find the latitude. Hour angle 4 39m 168 = 69° 49' log. cosine 9.53785 table 44 Star's pol. dist. in miles 72'.9 log. 1.86273 log. 1.40058 64 42 42 The following examples are worked by the method given in the Nautical Almanac, the necessary table being included here. The four problems cover all the conditions pertaining to this observation. Either of the two methods will be accepted by the examiner. EXAMPLE: September 8, 1902. The true altitude of the Pole Star out of the meridian was 41° 40′ 30′′. Greenwich mean time 4h 16m A. M. Longitude by account 30° 19' 15" W. Find the latitude. EXAMPLE: October 27, 1902. Local mean time 10h 40m 30s P. M. Longitude by account 29° 00' E. Star was 43° 20′. L. M. T. Long. 29° E. G. M. T. L. M. T. The true altitude of the Pole Table for Finding the Latitude by an Observed Altitude of Polaris taken from the Nautical Almanac for 1902. Reduce the observed altitude of Polaris to the true altitude. Reduce the recorded time of observation to the local sidereal time. If the local sidereal time is less than 1 24.1m, subtract it from 1h 24.1m; between 1 24.1m and 13h 24.1m, subtract 1 24. 1m from it; greater than 13h 24.1m, subtract it from 25h24.1m; and the remainder is the hour angle of Polaris. With this hour angle take out the correction from Table IV (below), and add it to or subtract it from the true altitude, according to its sign. The result is the approximate latitude of the place. |