On 22 July at 0720 ZT, in DR position LAT 20°38.2'N, LONG 87°16.0'W, you observe the Moon's lower limb. The sextant altitude (hs) is 38°32.6, and the chronometer reads 01h 18m 14s. The chronometer is 01m 28s slow. The index error is 3.1' off the arc, and the height of eye is 68 feet. What is the azimuth (Zn) and intercept (a) of this sight from the assumed position?
• Sextant altitude corrections: index error, dip (height of eye), main altitude corrections to get Ho from hs • Time and GHA: applying chronometer error to get correct UTC, then using date/time to find the Moon’s GHA and declination in the Nautical Almanac • Intercept and azimuth: using AP (assumed position), LHA, and declination to get Hc and Zn, then comparing Hc to Ho for an toward (A) or away (T) intercept
• First, think through every correction needed to convert the sextant altitude (hs) to the observed altitude (Ho). Which corrections increase the altitude and which decrease it in this case? • After correcting the chronometer time, what is the exact UTC of the sight, and how would that lead you to the Moon’s GHA and declination for 22 July? • Once you have your assumed latitude and longitude, LHA, and declination, what general quadrant should the Moon be in relative to your position at that time, and does that match the azimuth choices given?
• Make sure you apply index error correctly: "off the arc" vs "on the arc" changes the sign of the correction • Confirm the chronometer correction (slow vs fast) is applied in the right direction to get the correct UTC • After finding Hc from sight reduction, double‑check whether Ho is greater or less than Hc so you can decide if the intercept is toward (A) or away (T) and eliminate inconsistent answer choices
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