On 29 April your 0530 zone time position was LAT 23° 04.0' S, LONG 162° 12.0' E. Your vessel was steaming on course 120° T at a speed of 9.0 knots. An observation of the Sun's upper limb was made at 0830 ZT. The chronometer read 09h 27m 32s and was slow 02m 24s. The observed altitude (Ho) was 24° 58.0'. LAN occurred at 1205 zone time. The observed altitude (Ho) was 52° 04.0'. What was the longitude of your 1200 zone time running fix?
• Running fix using two sun lines at different times • Using LAN (Local Apparent Noon) to determine longitude from the Sun • Correcting chronometer time (with rate) to get accurate GMT for sight reduction
• First, figure out the true times in UTC/GMT for both the 0830 ZT sight and for LAN using the chronometer information. How far apart in time are the two sights in minutes? • From the LAN sight, think about how longitude is obtained from the time of meridian passage compared with zone time. Is your longitude east or west of the time zone meridian? • For the 0830 sight, how far will the ship move (in NM and in minutes of longitude) between 0830 ZT and 1200 ZT on course 120°T at 9.0 knots? How does that shift the morning sun line to get a running fix at 1200?
• Be sure you have converted chronometer time to UTC correctly, including applying the chronometer error in the correct sense (slow vs. fast). • Confirm whether your time zone is east or west of Greenwich, and which standard meridian (in degrees) that implies for 0530, 0830, and 1200 ZT. • When advancing the 0830 line to 1200, double-check the distance run = speed × time calculation and that you are moving the line in the track direction (120°T), not along the bearing of the Sun.
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