On 17 March your 1845 DR position is LAT 25°10.0'N, LONG 66°48.0'W. You observe an unidentified star bearing 340°T at an observed altitude (Ho) of 66°25.1'. The chronometer reads 10h 47m 49s, and is 1m 54s fast. What star did you observe?
• Using chronometer time and chronometer error to find UTC (GMT) • Relating Local Hour Angle (LHA) and Greenwich Hour Angle (GHA) to identify a star • Comparing the star’s approximate position (declination and SHA) with your DR latitude and the observed bearing
• How do you correct the chronometer time using the given error to find the actual UTC of the sight? • Once you know the time in GMT, what star data do you look up in the Nautical Almanac, and which columns are most important for unidentified star sights? • Given your DR latitude and the star’s approximate declination, does the star’s observed altitude and bearing (340°T and 66°25.1') make sense for that particular body?
• Be sure you apply the chronometer error with the correct sign (fast vs slow) before any Almanac work • Verify that the chosen star’s declination is consistent with being high in the sky (altitude ~66°) at latitude 25°N and bearing near 340°T • Check that the star’s Sidereal Hour Angle (SHA) and the resulting LHA produce a body position that could yield the observed bearing and altitude from your DR position
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