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Polar Distance
Table 15-4.-Solar Ephemeris for May 1985 - 14070_350

Engineering Aid 1 - Advanced Structural engineering guide book
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Figure 15-12.-Three possible situations in determining latitude by meridian altitude observation. where: @ = latitude of place 6 = declination of observed body h = corrected observed altitude CASE II. When the body observed is toward the pole from the zenith, which is the case for circumpolar stars, you can get the latitude of the place of observation by using the following formulas: 0 = h f p. Use this formula only for circumpolar star  observations,  where  p  is  the  polar  distance (90°  -  6). CASE  III.  When  the  equator  is  between  the  body observed  and  the  zenith,  use  the  following  formula  to get the latitude: In the above situations, always remember that 6 and @  positive when they are located north of the equator and negative when south of it. Latitude by Altitude of the Sun at Noon You can observe the altitude of the sun by two methods. In the first method, you follow the sun just before it is about to cross the approximate meridian. In the second method, you set the line of sight of the transit in the plane of a known meridian and wait for the sun to cross the line of sight. At this instant take the reading of the vertical angle. In either method your main objective is to measure the sun’s altitude accurately. You should know the exact time so that you can compute the instant of local apparent noon. Then you will know exactly when you should be in the field to have everything ready just  before  the  instant  of  observation. If the instrument used is not a transit equipped with solar  prism  attachments,  set  the  horizontal  cross  hair tangent to the lower edge of the sun’s disk. By the first method  referred  to  above,  when  you  are  observing  for maximum altitude, follow the sun until it no longer rises. The moment the sun starts going down, record the vertical angle and determine the index error. In the second method above, the setting of the sun’s disk is similar to the first method except that you get the reading at the instant the sun crosses your known meridian. In either  method,  you  should  correct  the  altitude  observed in  the  field  for  index  error,  semidiameter,  parallax,  and refraction. You can eliminate index error in the second method  by  plunging  the  telescope  and  taking  another reading as fast as possible. The   declination   for   the   Greenwich   time corresponding to the instant of local noon is taken from a table of the Nautical Almanac, the  Solar  Ephemeris, or The Ephemeris. The table for May 1985, taken from The   Ephemeris,   published   by   Bureau   of   Land Management, U.S. Department of Interior, and prepared by   the   Nautical   Almanac   office,   U.S.   Naval 15-15







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