On 26 July your 1901 ZT position is LAT 28° 28' N, LONG 157° 16' E when you take an observation of Jupiter. The chronometer at the time of the sight reads 08h 54m 34s and is 06m 24s slow. The sextant altitude (hs) is 33° 51.5'. The index error is 2.8' off the arc, and the height of eye is 48 feet. What are the azimuth (Zn) and intercept (a) for this sight using the assumed position?
• Chronometer correction and conversion to GMT/UT1 from zone time (ZT) and known chronometer error • Using GHA Aries + SHA of Jupiter to find the GHA of Jupiter, then computing Local Hour Angle (LHA) from assumed longitude • Forming an assumed position (AP) and using Hc/Zn calculation + intercept (a = Ho − Hc) method
• First, think through the exact sequence to get the correct time of the sight: how do you use the chronometer reading and its known error together with the date and zone description to get UT? • Once you have UT, how do you obtain GHA Jupiter from the Nautical Almanac (step by step from GHA Aries and SHA Jupiter), and then turn that into LHA at your assumed longitude? • After applying all sextant corrections to get Ho, compare it to Hc from the sight reduction table or calculator: what does the sign of (Ho − Hc) tell you about whether the intercept is toward or away and how will that affect which choice is reasonable given the azimuth?
• Be certain you applied index correction (off the arc) with the correct sign before dip and refraction corrections to get Ho. • Confirm the direction of the intercept: if Ho > Hc the intercept is Toward; if Ho < Hc it is Away — then match this with the T/A in the answer choices. • Verify that your computed Zn quadrant makes sense for Jupiter’s approximate bearing from your latitude and local hour angle (east vs west of your meridian) so you can eliminate impossible azimuth options.
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