On 23 September your 1836 DR position is LAT 25° 18' S, LONG 162° 36' E. You observe an unidentified star bearing 022° T at an observed altitude (Ho) of 13° 16'. The chronometer reads 07h 34m 12s, and is 01m 54s slow. What star did you observe?
• Local Hour Angle (LHA) of Aries and how it relates to the LHA of a star through its Sidereal Hour Angle (SHA) • How your DR latitude and longitude and the star’s declination affect its bearing and altitude • What stars are normally seen low in the sky to the north or south from a latitude of about 25° S
• First, correct the chronometer time and think about what UTC (Greenwich time) you should use for the sight reduction tables or Nautical Almanac • Use your DR position, corrected time, and the date (near the September equinox) to find the GHA of Aries, then apply the star’s SHA to get its GHA and LHA • For each candidate star, picture (or compute) whether its declination and your latitude could give an altitude of about 13° on a bearing of about 022° T
• Make sure you apply the chronometer correction in the right direction (remember: a slow chronometer means the true time is later than indicated) • Check whether each star’s declination sign and size are consistent with being seen low on the horizon in the 022° T direction from latitude 25° S • Verify that at the given time of year and longitude, the chosen star could reasonably be above the horizon at about 13° altitude, not circumpolar or completely below the horizon
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