On 15 November your 0813 zone time (ZT) fix gives you a position of LAT 22°30.0'N, LONG 67°28.0'W. Your vessel is on course 164°T, and your speed is 13.5 knots. Local apparent noon (LAN) occurs at 1215 ZT, at which time a meridian altitude of the Sun's lower limb is observed. The observed altitude (Ho) for this sight is 49°46.0'. What is the latitude at 1200 ZT?
• Meridian altitude (LAN) sight and how it gives latitude • Run line / dead reckoning (DR) from an earlier fix to a later time • Difference between fix position at 0813 ZT and position at 1200 ZT given course and speed
• How far (in nautical miles) will you travel between 0813 ZT and 1200 ZT at 13.5 knots? Convert the time difference to hours first. • In which direction (toward the equator or toward the pole) will your latitude be changing on course 164°T? How does that affect the latitude between 0813 and 1200? • For a meridian altitude of the Sun, what simple relationship exists between your latitude, the Sun’s declination on 15 November, and the observed meridian altitude (Ho)? Think about whether you are the same or opposite hemisphere from the Sun.
• Be sure to convert minutes of time to tenths of an hour before multiplying by speed. • Confirm whether you should apply the latitude change from the DR run to the LAN latitude, or the reverse, to get the latitude at 1200 ZT. • Verify the Sun’s declination on 15 November and apply the correct sign (north or south) before using the LAN latitude formula.
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