On 8 August your 0400 ZT DR position is LAT 23°16.0'S, LONG 105°33.0'W. You are on course 295°T at a speed of 25 knots. What will be the zone time of sunrise at your vessel?
• Zone description (ZD) based on your longitude and how to convert between GMT/UT, LMT, and ZT • Using the Nautical Almanac sunrise tables: first find sunrise at the nearest whole latitude and then interpolate for your exact latitude if needed • Converting from the DR time of position and the vessel’s course and speed to find your longitude at sunrise, not just at 0400 ZT
• From 0400 ZT, how many hours will pass before sunrise, and where will the ship be (DR position) at that later time? • What is the relationship between longitude and the time of sunrise at a given latitude—does sunrise occur earlier or later as you move west? • Once you have sunrise time in GMT (UT) or LMT, what exact step converts that to zone time for the longitude you’re in?
• Confirm the correct ZD for 105°33.0'W and use the correct sign when converting between GMT and ZT • Make sure you update your DR position from 0400 ZT to the approximate time of sunrise before entering the almanac tables • After computing the time, double-check that the final value is expressed in zone time (ZT), not GMT or LMT, and that it matches the local date (8 August)
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