On 22 March your 0519 ZT DR position is LAT 27° 20.6' N, LONG 69° 25.6' W. You observe an unidentified star bearing 094° T, at an observed altitude (Ho) of 30° 15.0'. The chronometer reads 10h 16m 47s and is 02m 15s slow. What star did you observe?
• Chronometer correction and UTC time – how to apply a chronometer error that is "slow" • Local hour angle (LHA) and how it links DR longitude, GHA Aries, and star SHA • Use of the Nautical Almanac star pages (or sight reduction tables) to match a computed intercept and azimuth to a specific star
• First, adjust the chronometer time using the stated error and convert it to the correct UTC time at the instant of the sight. Then relate that to the given zone time (ZT) and your longitude. • Next, think about how you would compute GHA Aries at the time of the sight, then obtain the GHA of each candidate star using GHA Aries + star’s SHA. • For each candidate star, consider how its computed altitude and azimuth from your DR position would compare with the observed Ho and the given true bearing. Which one will be consistent with both the altitude and direction?.
• Be sure you apply the chronometer error correctly: a slow chronometer means the true time is later than what the chronometer shows. • Verify that your LHA for each candidate is in the correct range and sign (0°–360°) after combining DR longitude with GHA. • Confirm that the star you select fits both: (1) an azimuth close to 094° T from your DR, and (2) a computed altitude close to 30° 15.0'—do not rely on just one of these.
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