On 13 October your 0515 zone time fix gives you a position of LAT 26°53.0'N, LONG 90°05.0'W. Your vessel is on course 068°T, and your speed is 7.8 knots. Local apparent noon (LAN) occurs at 1145 zone time, at which time a meridian altitude of the Sun's lower limb is observed. The observed altitude (Ho) for this sight is 54°51.5'. What is the latitude at 1200 ZT?
• Latitude by meridian altitude using the Sun's lower limb at LAN • Converting time difference between fix and LAN into distance run using speed (D = S × T) • Determining whether you are north or south of the Sun’s declination and how that affects the latitude formula
• From 0515 ZT to 1145 ZT, how many hours and decimal hours pass, and how far do you travel at 7.8 knots during that time? • At LAN, your Sun sight gives you Ho. How do you use Ho and the Sun’s declination at meridian passage on 13 October to find your latitude? (Think: Zenith distance = 90° − Ho) • Are you on the same side of the equator as the Sun? Should the zenith distance be added to or subtracted from the declination to get your latitude?
• Make sure you convert time to hours correctly before multiplying by speed to get distance in nautical miles. • Check the sign and value of the Sun’s declination for 13 October at LAN (N or S?) and apply the correct latitude formula for meridian altitude. • After applying the meridian altitude formula, remember to advance your 0515 latitude by the north–south component of your run along course 068°T (using basic traverse: distance × cosine of course angle from north).
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