At 1337 ZT on July 17, in DR position LAT...

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Question 1 of 2066636eea28f7522a1c51aaaf

At 1337 ZT on July 17, in DR position LAT 30° 56.8' S, LONG 039° 36.5' W, you observe an amplitude of the Moon. The upper limb of the moon is on the visible horizon, bearing 263.0° psc. The variation is 20° W. What is the deviation?

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🔍 Key Concepts

• Amplitude of the Moon as a check on compass error (difference between TRUE and COMPASS bearings) • Relationship: Compass bearing = True bearing + Variation + Deviation (keeping a consistent sign convention) • How to get the Moon’s true amplitude from the Nautical Almanac (using date, GMT, and DR latitude)

💭 Think About

• From your DR latitude and the Moon’s declination at the time, what should the true amplitude be (east or west of true north/south)? • Once you have the true amplitude, how do you turn that into a true bearing of the Moon’s center, and then compare it to the observed COMPASS bearing of the upper limb? • After you find compass error (difference between true and compass), how do you separate that error into variation and deviation, including the correct E/W sign?

✅ Before You Answer

• Be sure you convert from upper limb on the visible horizon to the correct center amplitude/bearing (apply the proper limb correction). • Confirm the sign of variation 20° W and how it enters your formula (does it add or subtract in your setup?). • Double‑check whether a westerly deviation makes the compass read higher or lower than true, and use that to verify the sign of your final answer.

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