On 1 July your 0515 ZT fix gives you a position of LAT 24°36.0'S, LONG 151°42.0'W. Your vessel is on course 300°T, and your speed is 10.0 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 42°55.0'. What is the calculated latitude at LAN?
• Running fix and dead reckoning (DR) position between a morning fix and LAN • Meridian altitude (LAN) sight used to determine latitude: Lat = (90° - Ho) + Dec (with attention to LHA and same/contrary name) • Change in DR latitude between 0515 and 1215 based on course and speed
• From 0515 to 1215, what is the elapsed time, and how many miles will you travel at 10 knots? • On course 300°T, how much of that track is north-south, and how does it change your latitude from the 0515 fix to the DR at 1215? • Once you have the DR latitude at LAN, how does the observed meridian altitude of the Sun adjust your DR latitude to a calculated latitude?
• Be sure to compute DR latitude at 1215 ZT first before applying the LAN sight; do not use the 0515 latitude directly. • Confirm the north-south component of the course using cos of the course angle from north-south, and convert minutes of arc to degrees correctly. • Apply the correct meridian latitude formula for the Sun at LAN, paying close attention to whether the Sun’s declination and your latitude are the same name or contrary name.
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