On 18 August at 0600 ZT, morning stars were observed, and the vessel's position was determined to be LAT 19°48'N, LONG 108°34'W. Your vessel is steaming on course 166°T at a speed of 16 knots. An observation of the Sun's lower limb is made at 1036 ZT. The chronometer reads 05h 34m 48s and is slow 01m 24s. What is the computed altitude (Hc) and azimuth (Zn) for this 1036 ZT observation using the assumed position method?
• Assumed position method for sight reduction (latitude and longitude adjustments) • Converting zone time (ZT) to Greenwich Mean Time (GMT/UTC) using chronometer reading and error • Using DR (dead reckoning) to advance the 0600 ZT position to 1036 ZT before choosing an assumed position
• How do you advance your 0600 ZT position to 1036 ZT using the given course and speed before working the sight? • Once you have UTC of the sight from the chronometer and its error, which Nautical Almanac values do you need to extract for the Sun, and how do they feed into Hc and Zn? • When choosing your assumed latitude and longitude, how do you round them to make the LHA and interpolation easy, and how might small changes in assumed position affect Hc and Zn?
• Be sure you correctly compute the time interval between 0600 ZT and 1036 ZT and convert the vessel’s run to minutes of latitude and change in longitude. • Double‑check the chronometer correction: a slow chronometer means you must add its error to the reading to get UTC (verify the sign carefully). • Confirm that the resulting Hc values are reasonable for a morning Sun sight in about 20°N latitude and 108°W longitude (high altitude from the east-southeast sector).
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