At 1620 ZT on 10 September, in DR position...

Question 1 of 2707066636eea28f7522a1c51ab31

At 1620 ZT on 10 September, in DR position LAT 34° 03.8' N, LONG 050° 28.4' W, you observe an amplitude of the Moon. The Moon's upper limb is observed on the visible horizon and bears 110.2° psc. The variation is 2° E. What is the deviation?

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Question 1 of 27070

🔍 Key Concepts

• Using an amplitude of the Moon to find true bearing and compass error • Relationship between true bearing, magnetic bearing, variation, and deviation • Converting an amplitude (measured from East/West point) into a true azimuth (bearing from north)

💭 Think About

• From the DR latitude and the Moon’s declination (from the Nautical Almanac), what is the computed true amplitude, and is it north or south of East/West? • Once you have the true amplitude, how do you convert it to a true bearing from north (0°–360°) so you can compare it with the observed compass bearing 110.2° psc? • Given that variation is 2°E, what must the deviation be so that: true bearing → magnetic bearing → compass bearing (or the reverse) matches your observed 110.2° psc?

✅ Before You Answer

• Be sure your amplitude sign and quadrant are correct (is the Moon rising or setting, and in which hemisphere?). • Check your conversion between amplitude and true azimuth: are you measuring from the correct reference (East/West vs North)? • Confirm your sign convention: remember that Easterly errors (variation or deviation) are added when going from true to compass and subtracted when going from compass to true ("True Virgins Make Dull Company").