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Yachtmaster Ocean revision module 6 of 10

COMP

Compass Checks by Celestial Body

Using sun, moon, star, or planet bearings to check compass error.

compass checkazimuth

3 guided lessons · 8 practice questions · 8 flashcards

3 outcomes · self-guided revision
  • Explain using sun, moon, star, or planet bearings to check compass error.
  • Apply compass check to a realistic onboard situation.
  • Recall the core check: the bearing observation and calculated azimuth must refer to the same time.

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Lesson routeWhy Use a Celestial Compass Check0/1 read

Lesson 1 of 1

Why Use a Celestial Compass Check

On an ocean passage, a celestial body can provide an independent true bearing for checking compass error. The Sun is common, but the Moon, stars, or planets can also be used when identified and visible.

The principle is simple: calculate or obtain the body's true azimuth, observe its compass bearing at the same time, then compare true, variation, and compass to derive deviation or compass error.

  • The bearing observation and calculated azimuth must refer to the same time.
  • Identify the body correctly.
  • Apply variation with the correct sign.
  • Record heading and magnetic environment when checking deviation.
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