On 22 March your 0519 DR position is LAT 27°...

Question 1 / 2066636eea28f7522a1c51ad08

Question 1 of 2066636eea28f7522a1c51ad08

On 22 March your 0519 DR position is LAT 27° 20.6' N, LONG 69° 25.6' W. You observe an unidentified star bearing 051° T at an observed altitude (Ho) of 50° 03.7'. The chronometer reads 10h 16m 47s, and is 02m 15s slow. What star did you observe?

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🔍 Key Concepts

• Chronometer correction and GMT – how to convert the chronometer reading and known error into the correct UTC time for the sight reduction. • DR position and true bearing – using the dead reckoning latitude/longitude and true bearing to narrow down which stars are in that direction at that time. • Nautical Almanac / Star Identification – matching the Local Hour Angle (LHA) and declination of candidate stars with the observed altitude and azimuth.

💭 Think About

• First convert the chronometer time to correct UTC by applying the 02m 15s slow error. From there, determine the approximate Greenwich Hour Angle (GHA) of Aries for that date and time. • From your DR longitude and the GHA of Aries, find Local Hour Angle (LHA) Aries and then the approximate sidereal hour angle for a star in the 051° T direction. Which of the listed stars has a position (SHA/Dec) that would put it near that azimuth and altitude from your DR at that time? • Compare the expected computed altitude (Hc) and azimuth (Zn) for each candidate star with the observed altitude (Ho 50° 03.7') and bearing 051° T. Which one is most consistent?

✅ Before You Answer

• Be sure you apply the chronometer error in the correct sense: a slow chronometer means the true time is later than indicated. • Check that your DR longitude is used with the correct sign (West longitude added to GHA to get LHA in the usual convention). • Confirm that the star you choose has a declination that would place it at about 50° altitude when observed from latitude 27° N on that date and at a bearing close to 051° T.

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Question 1 / 2066636eea28f7522a1c51ad08

Question 1 of 2066636eea28f7522a1c51ad08

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Question 1 of 20

66636eea28f7522a1c51ad08

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🔍 Key Concepts

💭 Think About

✅ Before You Answer

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