On 12 September your 0600 zone time (ZT) fix gives you a position of LAT 22°51.9'N, LONG 133°40.1'W. Your vessel is on course 062°T, and your speed is 12.3 knots. Local apparent noon (LAN) occurs at 1142 ZT, at which time a meridian altitude of the Sun's upper limb is observed. The observed altitude (Ho) for this sight is 70°33.2'. What is the calculated latitude at LAN?
• Meridian altitude (LAN) sight and how it relates directly to latitude • How to compute DR latitude at LAN using course, speed, and time run from the 0600 fix • The basic noon-sight latitude relationship: Lat = (90° − Ho) +/− declination and how to choose the sign
• From the 0600 ZT fix to 1142 ZT, how long have you been steaming, and how much latitude do you gain or lose on course 062°T at 12.3 knots? Focus on the north–south component of your track. • Once you have DR latitude at LAN, how do you combine the Sun’s observed meridian altitude (Ho) with its declination to adjust that DR latitude and get a more accurate latitude? • Is the Sun north or south of you at LAN, and does the observed altitude put the Sun north or south of your zenith? How does that affect whether you add or subtract declination in the noon‑sight formula?
• Compute the time interval from 0600 to 1142 ZT correctly in hours and decimals, then multiply by speed to get distance made good. • Resolve your track on 062°T into a meridional (north–south) component using cosine of the course angle from north to find the change in latitude. • Make sure you apply the correct sign convention in the noon-sight formula: decide carefully whether you should add or subtract the Sun’s declination from (90° − Ho) based on relative positions.
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