On 8 April your evening DR position is LAT...

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Question 1 of 2066636eea28f7522a1c51ae50

On 8 April your evening DR position is LAT 22° 16' N, LONG 157° 58.3' W. You observe an unidentified star bearing 246° T at an observed altitude (Ho) of 58° 45.5'. The chronometer reads 05h 09m 57s, and is 01m 23s slow. What star did you observe?

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Question 1 of 20

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🔍 Key Concepts

• Use the DR position, observed altitude (Ho), and time to find the Greenwich Hour Angle (GHA) of Aries and then the Local Hour Angle (LHA) of Aries • From the Nautical Almanac, compare each star’s Sidereal Hour Angle (SHA) and Declination (Dec) with your computed LHA and latitude • Relate the star’s computed azimuth and altitude to the observed true bearing 246° T and Ho = 58° 45.5'

💭 Think About

• How do you adjust the chronometer time using the chronometer error (slow/fast) to get the correct Greenwich Mean Time (GMT) for the sight? • Once you have GHA Aries, what step converts that to Local Hour Angle (LHA) Aries at your DR longitude, and how is that then used with each star’s SHA? • For each candidate star, how would its SHA/Dec and your DR position affect the approximate bearing and altitude—which ones can you quickly rule out as being in the wrong part of the sky?

✅ Before You Answer

• Be sure you applied the chronometer error (01m 23s slow) in the correct direction when finding GMT • Confirm the sign and sense of your west longitude when computing LHA (LHA = GHA ± LONG)—a sign mistake can put the star in the wrong hemisphere of the sky • Check that the chosen star’s Declination is reasonable for a star seen at about 58° altitude from latitude 22° N; very high or very low declinations may not fit this geometry

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