On 27 June your vessel's 0816 ZT DR position is LAT 22°14'S, LONG 53°52'W, when an azimuth of the Sun is observed. The chronometer time of the sight is 12h 15m 02s, and the Sun is bearing 047.5° per standard magnetic compass. The chronometer error is 00m 46s slow, and the variation in the area is 6.0°E. What is the deviation of the standard magnetic compass?
• Azimuth of the Sun used to find compass error (CE) and then deviation • Relationship between true bearing, magnetic bearing, compass bearing, variation, and deviation • Correcting the chronometer time and determining the Sun’s true azimuth at the DR position and time
• How do you go from the observed compass bearing of the Sun to a true bearing using variation and deviation? Think about the standard correction sequence. • What steps are needed to turn the chronometer time with error into the correct UTC/GMT to enter the Nautical Almanac, and why does that matter for the Sun’s azimuth? • Once you compute the true azimuth of the Sun from the Almanac and sight reduction, how do you compare it to the compass bearing to extract compass error and then deviation?
• Be sure you apply the chronometer error with the correct sign (slow vs fast) when finding UTC. • Keep the correction order straight: True ↔ Magnetic ↔ Compass; track whether you are moving from true to compass or compass to true. • Check whether your final computed deviation is east or west by seeing which way the compass is deflected from magnetic.
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