At 0600 ZT on 24 July your DR position is LAT 22°37'N, LONG 32°45'W. You are steering 185°T at a speed of 20.0 knots. Determine the computed altitude (Hc) and azimuth (Zn) for an observation of the Sun's lower limb taken at 1030 ZT. At this time the chronometer reads 00h 30m 16s and is 0m 31s slow.
• DR position advance from 0600 to the time of sight using course and speed • Conversion of zone time (ZT) and chronometer error to correct GMT/UT1 for entering the Nautical Almanac • Using the assumed position with GHA/Dec of the Sun to find Hc and Zn via sight reduction tables or formulas
• How far (in miles) do you travel between 0600 and the actual time of the sight, and what is your new DR latitude and longitude? • Once you know the true GMT of the sight, what are the Sun’s GHA and declination, and how do you choose an assumed longitude and latitude close to your DR? • Given the assumed position and the Sun’s GHA/Dec, what pattern of Hc and Zn would you expect as you move slightly east/west or north/south?
• Be sure you apply the chronometer correction in the correct direction since the chronometer is specified as slow or fast • Confirm your run calculation: time interval in hours × 20.0 knots, then convert to degrees of latitude/longitude correctly for your latitude • Before comparing to the choices, check whether the Sun should be east or west of your meridian at that time and in that ocean area; this helps you judge if the azimuth (Zn) angle is reasonable
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