On 5 April at 0509 zone time, morning stars were observed and the vessel's position was LAT 28°32'N, LONG 177°13.0'W. Your vessel is steaming at 19.0 knots on a course of 258°T. A sextant observation of the Sun's lower limb is made at 1021 zone time. The chronometer reads 10h 20m 09s, and the sextant altitude (hs) is 58°06.6'. The index error is 1.0' off the arc, and the chronometer error is 00m 54s slow. Your height of eye on the bridge is 55.0 feet. What is the azimuth (Zn) of this sight using the assumed position?
• Azimuth (Zn) definition and how it is measured from true north through 360° • Steps for reducing a sextant sight: applying index correction, dip (height of eye), and converting hs → ho • Using the assumed position, GHA and Dec of the Sun at the observed time to compute LHA and then azimuth
• First, think about how to correct the sextant altitude hs using index error and height of eye. What corrections are applied, and in what order, to get the observed altitude ho? • Consider whether the Sun is to the NE, SE, SW, or NW of your position at the given date, time, latitude, and longitude. How does that general direction limit the possible azimuth values? • After finding LHA and declination for the Sun at the sight time, recall which sight-reduction formulas or tables give you the azimuth angle, and how that angle is converted to Zn in true degrees.
• Confirm the sign and application of the index error: "off the arc" vs "on the arc" and whether you add or subtract it from hs • Verify the chronometer correction: the chronometer is 00m 54s slow—how do you adjust the chronometer reading to get the correct UTC for the sight? • Make sure you correctly determine whether the Sun is in the eastern or western half of the sky at 1021 local time at 177°W, since that directly affects the quadrant of the azimuth Zn.
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