On 10 August your vessel's 0426 zone time DR position is LAT 52°07'N, LONG 142°16'E, when an amplitude of the Sun is observed. The Sun's lower limb is about 20 minutes of arc above the visible horizon and bears 074.5° per standard compass. Variation in the area is 12°W. The chronometer reads 07h 24m 19s and is 02m 34s fast. Which of the following is the deviation of the standard compass?
• Amplitude of the Sun to find compass error (difference between true and observed bearing) • How to get true bearing of the Sun at the time of observation using date, latitude, and Sun’s declination • Relationship among true bearing, variation, deviation, and compass course: T → M → C
• First, think about how you correct the chronometer time and why you need an approximate local hour angle (LHA) or azimuth for the Sun when doing an amplitude check. • Ask yourself: once I know the Sun’s true bearing at rising/setting, how do I compare that with the standard compass bearing to get total compass error? • After I find total compass error, how do I separate it into variation and deviation to get the deviation alone?
• Be sure you are using the correct declination of the Sun for 10 August at the correct GMT (UT) — from the Nautical Almanac. • Check that you are applying signs correctly when going from true to magnetic to compass (east/west rules for variation and deviation). • Verify that you are using the standard compass bearing of the Sun (074.5°) and not confusing it with a gyro or magnetic compass reading.
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