On 7 November your 0830 zone time fix gives you a position of LAT 27°36.0'N, LONG 163°19.0'W. Your vessel is on course 289°T, and your speed is 19.0 knots. Local apparent noon (LAN) occurs at 1138 zone time, at which time a meridian altitude of the Sun's lower limb is observed. The observed altitude (Ho) for this sight is 45°35.0'. What is the calculated latitude at LAN?
• Meridian altitude (LAN) sight and how it relates directly to latitude • Using the Sun’s declination on the given date and applying the proper meridian altitude formula • Effect of run between 0830 and LAN on your DR latitude versus fix latitude
• First, figure out how many minutes you run between the 0830 fix and LAN, and how many miles north/south you move in that time based on your course and speed. • Recall the standard meridian altitude relationship between latitude, declination, and observed meridian altitude (Ho). Think about whether you add or subtract declination and which sign (N/S) matters. • Compare your DR latitude at LAN (from running the fix forward) to the latitude you get from the meridian altitude calculation. Which of the answer choices best matches the meridian altitude result, not just the DR?
• Be sure to get the DR latitude at 1138 ZT by advancing only the north/south component of your course from 0830 to 1138. • Look up the Sun’s declination for 7 November and check whether it is north or south; this controls whether you add or subtract in the meridian altitude formula. • Verify that you are using Ho at meridian passage, not an intercept sight formula (no LOP, just direct latitude from LAN).
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