At 1502 ZT on 4 August, in DR position LAT...

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Question 1 of 2066636eea28f7522a1c51aaf4

At 1502 ZT on 4 August, in DR position LAT 11° 21.6' S, LONG 088° 14.3' E, you observe an amplitude of the Moon. The upper limb of the Moon is on the visible horizon and bears 289° psc. The variation is 15° W. What is the deviation?

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Question 1 of 20

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🔍 Key Concepts

• Use an amplitude of the Moon to find the compass error (difference between true bearing and compass bearing at the horizon) • Remember the relationship: Compass Error = Variation + Deviation (watch the algebraic signs: East is positive, West is negative or vice versa, but be consistent) • Convert the observed bearing 289° psc into a true amplitude using your sight reduction steps, then compare true vs. compass

💭 Think About

• From the DR latitude and the Moon’s declination (from the appropriate almanac page), determine whether the Moon is rising or setting and whether the amplitude is north or south of west • Figure out the true bearing of the Moon when it is on the visible horizon, then compare that true bearing with the observed psc bearing 289° to get the compass error • Once you have compass error and know variation is 15° W, solve for deviation with correct sign

✅ Before You Answer

• Be sure you are using upper limb of the Moon and the correct semitangent/semi-diameter correction for amplitude (per your tables or method) • Check that you have the correct sign for the amplitude (N or S of west) before turning it into a true azimuth/bearing • Before picking an answer, confirm whether your computed deviation should come out East or West, then match the magnitude and direction to the closest choice

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