On 16 February your 0640 zone time (ZT) position was LAT 23°46.0'N, LONG 156°24.0'W. Your vessel was steaming on course 222°T at a speed of 18.0 knots. An observation of the Sun's lower limb was made at 0910 ZT. The chronometer read 07h 08m 06s and was slow 01m 56s. The observed altitude (Ho) was 27°15.8'. LAN occurred at 1245 ZT (ZD +10). The observed altitude (Ho) was 55°25.3'. What was the longitude of your 1245 ZT running fix?
• Longitude by chronometer using a Sun sight before LAN • Using a running fix: advancing an earlier line of position (LOP) to the later time • Relationship between time difference from LAN and change in longitude while steaming on a known course and speed
• How do you convert the chronometer reading, with its known error, into Greenwich Mean Time (GMT/UT) at the time of the 0910 ZT sight? • Once you have GMT for the 0910 sight, how do you find the Sun’s GHA and then your longitude from that first LOP? • Between 0910 ZT and 1245 ZT, how far did the vessel travel along 222°T at 18 knots, and how does that distance and course let you advance the 0910 LOP to 1245 and obtain the running fix longitude? • How does the fact that LAN was at 1245 ZT with Sun Ho 55°25.3' help confirm you are near local apparent noon and so close to your meridian longitude at that time?
• Be sure to apply the chronometer error correctly (slow vs fast) when finding GMT • Confirm the time interval between 0910 ZT and 1245 ZT and the corresponding distance run at 18.0 knots • Check that you are using the correct sign (east or west) when converting GHA and assumed longitude to local hour angle (LHA) and when updating longitude for the run between sights
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