Figure 15-12.-Three possible situations in determining latitudeby meridian altitude observation.where:@ = latitude of place6 = declination of observed bodyh = corrected observed altitudeCASE II. When the body observed is toward thepole from the zenith, which is the case for circumpolarstars, you can get the latitude of the place of observationby using the following formulas:0 = h f p. Use this formula only for circumpolarstar observations, where p is the polar distance(90° - 6).CASE III. When the equator is between the bodyobserved and the zenith, use the following formula toget the latitude:In the above situations, always remember that 6 and@positive when they are located north of the equatorand negative when south of it.Latitude by Altitudeof the Sun at NoonYou can observe the altitude of the sun by twomethods. In the first method, you follow the sun justbefore it is about to cross the approximate meridian. Inthe second method, you set the line of sight of the transitin the plane of a known meridian and wait for the sun tocross the line of sight. At this instant take the reading ofthe vertical angle. In either method your main objectiveis to measure the sun’s altitude accurately. You shouldknow the exact time so that you can compute the instantof local apparent noon. Then you will know exactlywhen you should be in the field to have everything readyjust before the instant of observation.If the instrument used is not a transit equipped withsolar prism attachments, set the horizontal cross hairtangent to the lower edge of the sun’s disk. By the firstmethod referred to above, when you are observing formaximum altitude, follow the sun until it no longer rises.The moment the sun starts going down, record thevertical angle and determine the index error. In thesecond method above, the setting of the sun’s disk issimilar to the first method except that you get the readingat the instant the sun crosses your known meridian. Ineither method, you should correct the altitude observedin the field for index error, semidiameter, parallax, andrefraction. You can eliminate index error in the secondmethod by plunging the telescope and taking anotherreading as fast as possible.The declination for the Greenwich timecorresponding to the instant of local noon is taken froma table of the Nautical Almanac, the Solar Ephemeris,or The Ephemeris. The table for May 1985, taken fromThe Ephemeris, published by Bureau of LandManagement, U.S. Department of Interior, and preparedby the Nautical Almanac office, U.S. Naval15-15