On 14 January your 0550 DR position is LAT...

Question 1 of 31048HMmaGQaG9bjKqZ2jNK81

On 14 January your 0550 DR position is LAT 25°26.0'N, LONG 38°16.0'W. You observe an unidentified star bearing 043°T at an observed altitude (Ho) of 37°12.1'. The chronometer reads 08h 48m 51s, and is 01m 22s slow. What star did you observe?

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Question 1 of 31048

🔍 Key Concepts

• Chronometer correction and UTC – how to convert the given chronometer time and error into the correct GMT/UTC for the sight. • Sidereal Hour Angle (SHA) and declination – how these, with your DR latitude and LHA Aries, determine a star’s approximate bearing and altitude. • Star identification by intercept – comparing a computed altitude (Hc) and true bearing (Zn) for each candidate star with the observed altitude (Ho) and bearing.

💭 Think About

• First, convert the chronometer reading and its error into the correct UTC. What approximate Greenwich Hour Angle (GHA) of Aries will that give you on 14 January? • Given your DR latitude and longitude, which candidate star’s declination places it in the correct hemisphere and altitude range (around 37°) from your position? • If you compute Hc and Zn using one candidate’s SHA and declination, does the resulting true bearing come out close to the observed 043°T, and is the difference between Ho and Hc small?

✅ Before You Answer

• Be sure you apply the chronometer error with the correct sign (a slow chronometer means true time is later). • Check that the declination sign and magnitude of the candidate star are consistent with your DR latitude and the observed altitude (a northern star vs a southern star from 25°N). • Verify that the candidate star’s computed azimuth (Zn) is reasonably close to 043°T before worrying about small intercept differences.