On 17 March your 0520 DR position is LAT 27° 23.0' N, LONG 39° 42.0' W. At this time you observe an unidentified star bearing 270° T with an observed altitude of 46° 30.2'. The chronometer reads 08h 22m 15s, and is 01m 45s fast. What star did you observe?
• Local hour angle (LHA) and how it relates to GHA and longitude • Using the chronometer error to find the correct UTC time of the sight • Relating bearing of the star to its approximate azimuth and sky position
• How do you correct the chronometer reading to get the actual UTC of the sight, and why is that important for identifying the star? • Once you know UTC, how can you use the DR longitude with GHA Aries and the star’s SHA to find its local hour angle and compare with the observed bearing? • Looking at the choices, which of these stars is generally found near the west at that time of year and night, and at a mid‑northern latitude of about 27° N with an altitude near 46°?
• Be sure you apply the chronometer error in the correct direction (fast vs. slow) when finding UTC. • Confirm that your computed azimuth from sight reduction is reasonably close to the observed bearing 270° T. • Check that the star’s declination and magnitude are consistent with an altitude of about 46° from latitude 27° N at that local hour angle.
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