At 1820 zone time, on 21 March, you depart San Francisco, LAT 37° 48.5' N, LONG 122° 24.0' W (ZD +8). You are bound for Melbourne, LAT 37° 49.2' S, LONG 144° 56.0' E, and you estimate your speed of advance at 21 knots. The distance is 6,970 miles. What is your estimated zone time of arrival at Melbourne?
• Time zone conversion using zone description (ZD) when changing longitude and crossing the International Date Line • Relationship between distance, speed, and time: time of voyage in hours and days • How to convert zone time of departure to GMT/UTC, then to zone time of arrival
• First, compute how many hours and days it will take to travel 6,970 miles at 21 knots. Is the result an exact number of days or days plus hours? • Convert the 1820 zone time of departure (ZD +8) to UTC. Once you have UTC departure time, add the voyage time you calculated. • Determine the approximate longitude of the date line crossing and how the zone description changes from the U.S. West Coast to Melbourne. When you convert final UTC to Melbourne local time, do you need to add or subtract hours, and do you cross the date line (changing the date)?
• Double-check your time of voyage calculation: use ( \text{Time} = \frac{\text{Distance}}{\text{Speed}} ) and convert decimal days to days and hours correctly. • Verify that when you go from ZD +8 (San Francisco) to Melbourne’s zone description, your sign (east vs. west) and add/subtract direction for time are consistent. • After you get a candidate arrival date/time in Melbourne’s zone, quickly estimate: at 21 knots for almost 7,000 miles, is an arrival around early April or later? This can help eliminate clearly unreasonable options.
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