On 22 March your 1834 ZT DR position is LAT...

Question 1 / 2066636eea28f7522a1c51ad0e

Question 1 of 2066636eea28f7522a1c51ad0e

On 22 March your 1834 ZT DR position is LAT 26°13.5' S, LONG 108°36.5' W. You observe an unidentified star bearing 077°T, at an observed altitude (Ho) of 43°10.5'. The chronometer reads 01h 32m 37s and is 01m 50s slow. What star did you observe?

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🔍 Key Concepts

• Chronometer correction and GMT – Convert the given chronometer time and apply the slow error correctly to get the actual UTC of observation. • GHA Aries and LHA of the assumed position – From the correct UTC, determine GHA Aries, then local hour angle (LHA) and hour angle of the star to help identify it. • Star identification triangle – Compare your computed intercept and azimuth with typical positions of candidate stars (Regulus, Menkar, Rigel, Alphard) for that date, time, and DR position.

💭 Think About

• First, carefully convert the ship’s zone time (ZT) to UTC for the DR position date, then correct the chronometer time using the given slow error. Are you sure you’re using the right sign on the correction? • Once you have UTC, think about how you would obtain or approximate GHA Aries and Dec of each candidate star for that moment. Which one would be in the NE quadrant with a bearing near 077°T and an altitude around 43° at that latitude? • Consider the DR latitude 26°S: which of the listed stars (with their known declinations) would appear at a moderate altitude in the NE, rather than low on the horizon or very high overhead, at that time of year?

✅ Before You Answer

• Double-check the chronometer correction: a chronometer that is "01m 50s slow" means the actual time is later than indicated – are you adding or subtracting correctly? • Confirm the zone description (ZD) you should use near 108°W and how to convert 1834 ZT on 22 March to UTC on that date. • Verify the declination and approximate right ascension/Hour Angle of each candidate star and ask: which one’s position in the sky is consistent with a 077°T bearing and Ho ≈ 43° at LAT 26°S?

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Question 1 of 20

Regulus

Menkar

Rigel

Alphard

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Question 1 / 2066636eea28f7522a1c51ad0e

Question 1 of 2066636eea28f7522a1c51ad0e

Back

Question 1 of 20

66636eea28f7522a1c51ad0e

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🔍 Key Concepts

💭 Think About

✅ Before You Answer

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