On 12 June your 1845 DR position is LAT 21° 47' N, LONG 46° 52' W when you observe a faint unidentifiable star through a break in the clouds. The star bears 162° T at a sextant altitude (hs) of 28° 36.5'. The index error is 0.5'on the arc, and the height of eye is 45 feet. The chronometer reads 09h 43m 27s, and the chronometer error is 1m 46s slow. What star did you observe?
• Sight reduction for a star using DR position, time, and sextant altitude • Correcting sextant altitude (hs) to observed altitude (Ho) using index error and height of eye • Using the Nautical Almanac star data (Sidereal Hour Angle, declination, and magnitude) to identify a star
• After applying index error and dip, what is your Ho, and how does it compare with the computed altitude (Hc) from your DR position for each candidate star? • Given the corrected chronometer time and date, what is the approximate Greenwich Hour Angle (GHA) of Aries and the Local Hour Angle (LHA) for each possible star? • Which candidate star would be visible near the bearing 162° T and at that altitude from your DR latitude in June?
• Be sure you apply the index error sign correctly: "on the arc" vs. "off the arc" • Confirm your dip correction for 45 ft height of eye from the table before finding Ho • Check that the declination and hour angle of the chosen star place it in the correct part of the sky (south vs. north, and approximate azimuth 162° T) from LAT 21° 47' N
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