On 23 September your 1836 DR position is LAT 25° 18' S, LONG 162° 36' E. You observe an unidentified star bearing 148° T at an observed altitude (Ho) of 13° 32'. The chronometer reads 07h 34m 12s, and is 01m 54s slow. Which star did you observe?
• Using DR (dead reckoning) position, time, and observed altitude Ho to identify a star on a star‑finder or in sight reduction tables • Relationship between Local Hour Angle (LHA), Greenwich Hour Angle (GHA), and sidereal hour angle (SHA) for stars • How the star’s azimuth (Zn) from computation should compare with the observed true bearing of 148° T
• First, correct the chronometer time using its known slow error, then convert to Greenwich Mean Time (GMT/UT) and determine GHA Aries for that time; how does this help you find the star’s LHA? • From your DR longitude and computed LHA, what declination and SHA combination would put a star roughly south‑southeast (around 148° T) at an altitude of about 13.5° from your latitude 25° S? • After you compute an intercept and azimuth for each candidate star, which one gives an azimuth close to 148° T and a small intercept from the DR position?
• Be sure to apply the chronometer error with the correct sign (it is stated as slow – does that mean you add or subtract from the reading?). • Confirm you are using the correct DR longitude sign convention (East vs West) when computing LHA. • Verify that for the correct star, both computed altitude (Hc) is close to 13° 32' and computed azimuth (Zn) is close to 148° T from the DR position.
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