On 23 October in DR position LAT 21° 13.0'...

Question 1 / 2066636eea28f7522a1c51ad61

Question 1 of 2066636eea28f7522a1c51ad61

On 23 October in DR position LAT 21° 13.0' N, LONG 152° 18.0' E, you observe an amplitude of the Sun. The Sun's center is on the visible horizon and bears 259° psc. The chronometer reads 07h 21m 46s and is 01m 32s slow. Variation in the area is 5° E. What is the deviation of the magnetic compass?

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🔍 Key Concepts

• Amplitude of the Sun and how it gives you compass error (combined variation + deviation) at sunrise/sunset • Converting chronometer time (with known error) to UTC and then to LHA (Local Hour Angle) of the Sun using GMT and longitude • Relationship: True bearing → magnetic bearing → compass bearing, using variation and deviation signs correctly

💭 Think About

• First, from the chronometer reading and its error, what is the correct UTC at the moment of the observation? • Using the date, UTC, and DR longitude, what is the Sun’s calculated true amplitude and corresponding true bearing at the visible horizon? • Compare the true bearing of the Sun with the observed compass bearing to find total compass error, then separate that into variation and deviation—what sign (E or W) should the deviation have?

✅ Before You Answer

• Be sure you are using the correct sign for longitude (East vs West) when forming LHA and finding the Sun’s azimuth/amplitude. • Check that you apply variation (5° E) with the proper sign when moving between true and magnetic bearings. • Confirm that you’re comparing the correct bearings: observed bearing 259° psc is a compass bearing, not magnetic or true—keep the conversion steps in the right order.

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Question 1 of 20

0.9° E

1.5° W

5.9° W

6.5° E

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Question 1 / 2066636eea28f7522a1c51ad61

Question 1 of 2066636eea28f7522a1c51ad61

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Question 1 of 20

66636eea28f7522a1c51ad61

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🔍 Key Concepts

💭 Think About

✅ Before You Answer

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