At 1318 ZT on 10 September, in DR position...

Question 1 of 2707066636eea28f7522a1c51aaae

At 1318 ZT on 10 September, in DR position LAT 24° 05.8' N, LONG 058° 08.3' E, you observe an amplitude of the Moon. The upper limb of the Moon is on the visible horizon and bears 254° psc. Variation is 2° W. What is the deviation?

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Question 1 of 27070

🔍 Key Concepts

• Amplitude of the Moon and how to correct the observed bearing to get true azimuth • Effect of variation and deviation: True = Compass ± variation ± deviation (remember the correct sign convention) • How upper limb of the Moon and observer’s latitude affect computed (theoretical) amplitude

💭 Think About

• First, think about how to turn the observed compass bearing (psc) into a compass amplitude, then into a true amplitude using variation and deviation. • Consider how you would compute the theoretical true amplitude of the Moon from latitude and Moon’s declination, then compare that to your observed true amplitude. • Ask yourself: once you know both the calculated true amplitude and the observed true amplitude, how do you extract the sign and size of the deviation?

✅ Before You Answer

• Be clear on your sign convention: is West variation and West deviation considered plus or minus in your formula? • Verify whether you’re working with bearings (azimuths) or amplitudes (difference from East/West point) at each step. • Confirm you have correctly applied variation first, deviation second when converting between compass and true directions.