On 4 July at 0630 ZT, morning stars were observed, and the vessel's position was determined to be LAT 21°15.0'S, LONG 21°20.0'W. Your vessel is steaming at 13.0 knots on a course of 146°T. A sextant observation of the Sun's lower limb is made at 0915 ZT. The chronometer reads 10h 14m 27s, and the sextant altitude is 25°29.8'. The index error is 3.1' off the arc, and the chronometer error is 0m 53s slow. Your height of eye on the bridge is 48.0 feet. What is the azimuth (Zn) of this sight using the assumed position?
• Intercept (Marcq St. Hilaire method) and how the azimuth comes from the same sight-reduction process • Using the assumed position (AP) nearest to the DR position at time of sight • Looking up the Sun’s GHA and Dec for the correct UTC of observation, not ZT
• First, work the DR from the morning star fix to the time of the Sun sight so you know what latitude and longitude to use as your assumed position. Is the AP in the same latitude hemisphere as the DR? • When you reduce the sextant altitude to get Ho, compare it with Hc from the sight-reduction tables. While doing that, pay close attention to the latitude sign and the Sun’s declination sign—how do they affect the azimuth quadrant? • Once you find Z (the true azimuth angle) from the tables or formula, think: from which pole is it measured, and how do you correctly convert Z to Zn? Check whether the Sun is east or west of your meridian at the time of sight.
• Confirm you have correctly converted ZT to UTC using the appropriate time zone and then applied the chronometer error with the correct sign • Make sure all altitude corrections are applied in the right direction: index error, dip for height of eye, and main altitude corrections from the tables before using Ho • Double‑check: Is the local hour angle (LHA) between 0° and 360° in the correct direction (west), and does that LHA place the Sun to the correct side (east or west) to match the azimuth answer you choose?
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