On 15 August your 0512 zone time position was LAT 29° 18.0' N, LONG 57° 24.0' W. Your vessel was steaming on course 262° T at a speed of 20.0 knots. An observation of the Sun's lower limb was made at 0824 ZT. The chronometer read 00h 22m 24s and was slow 01m 34s. The observed altitude (Ho) was 38° 16.7'. LAN occurred at 1204 zone time. The observed altitude (Ho) was 74° 58.0'. What was the longitude of your 1204 zone time running fix?
• Zone time vs. GMT (UTC) conversion using chronometer error and watch time • How to advance a morning Sun line of position (LOP) to LAN to form a running fix • Using LAN (Local Apparent Noon) time to determine longitude from meridian passage of the Sun
• First, what is the exact GMT (UTC) of the 0824 ZT sight after you apply chronometer reading and chronometer error? How does that compare to the GMT of LAN? • Once you know the times, what time interval separates the morning sight from LAN, and how far does the vessel travel along its track in that interval? • At LAN, how is longitude related to the GMT of meridian passage compared to your zone time of LAN? How does that connect to your final longitude choice?
• Be sure you convert chronometer error with the correct sign (slow vs. fast) before using the time. • Confirm your DR (dead reckoning) track: course 262° T and 20.0 knots, and compute the distance run between the two sights. • Verify that you are using the LAN time method for longitude (difference between local apparent noon and GMT of the Sun’s meridian passage) consistently with the vessel’s zone time.
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