On 12 February your 0542 zone time (ZT) fix gives you a position of LAT 26° 42.0' N, LONG 60° 18.0' W. Your vessel is on course 300° T, and your speed is 9.8 knots. Local apparent noon (LAN) occurs at 1220 ZT at which time a meridian altitude of the Sun's lower limb is observed. The observed altitude (Ho) for this sight is 49° 10.0'. What is the calculated latitude at LAN?
• Meridian altitude (LAN) sight and how it relates directly to latitude • How to advance your 0542 ZT position to 1220 ZT using course, speed, and time run • Using the Sun’s declination on 12 February and the rule: Latitude ≈ (Zenith Distance) ± Declination
• First, compute how much time passes between 0542 ZT and 1220 ZT, then find how many miles you travel along course 300° T in that interval. • Think about how to determine your latitude from a meridian passage sight: how do you get zenith distance from Ho, and how is that combined with the Sun’s declination for the correct hemisphere? • Consider whether you need to combine your original DR latitude with a run to LAN, or whether the LAN sight itself gives you a fresh latitude, independent of your earlier fix.
• Be sure you correctly convert the time difference into hours and minutes and then to distance using Speed = Distance / Time. • Check that you are using the correct declination of the Sun for 12 February (and correct sign: N or S). • Verify that when combining zenith distance and declination, you’re applying the correct same-name / contrary-name rule for latitude vs. declination in your hemisphere.
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