At 2231 ZT on 14 July you are in DR position...

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Question 1 of 2066636eea28f7522a1c51ad3f

At 2231 ZT on 14 July you are in DR position LAT 34° 06' S, LONG 149° 47' W, when you observe an amplitude of Jupiter. The planet is about one Sun's diameter above the visible horizon and bears 257.1° psc. The variation is 15° E. What is the deviation?

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🔍 Key Concepts

• Amplitude of a celestial body and how it relates to true bearing (azimuth) at the time of observation • How to correct a psc (per standard compass) bearing to get a true bearing using deviation and variation • The sign convention for east and west variation/deviation and the saying "Compass Best, Error West / Compass Least, Error East"

💭 Think About

• First, think about what an amplitude observation is used for: are you checking your DR position, or checking your compass? Which one stays fixed, and which one might be in error? • From the DR latitude and date/time, what side of the horizon is Jupiter on, and is it rising or setting? How does that affect the expected true azimuth of the planet? • Compare the expected true azimuth with the observed 257.1° psc. If the compass is reading too high or too low compared to true, does that indicate west or east deviation?

✅ Before You Answer

• Be sure you convert psc → magnetic → true (or the reverse) in the correct order, and use the given 15° E variation with the correct sign. • Double‑check whether you should apply deviation before or after variation when going between compass and true bearings. • Confirm that the final deviation you find matches both the magnitude (0.5°, 1.5°, or 2.5°) and the correct direction (E or W) using a memory aid like "Compass Least, Error East".

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