Celestial Navigation · Time — Zone Description
What is the zone description for a vessel at longitude 142°00'W?
- A+10
- B−9 (subtract 9 hours from zone time to get GMT)
- C+9 (add 9 hours to zone time to get GMT)✓ Correct
- D+9.5
Explanation
Zone description = longitude ÷ 15, rounded to the nearest whole number: 142 ÷ 15 = 9.47 → 9. West longitude carries a plus sign (zones are slow on GMT), so ZD = +9: add 9 hours to zone time to obtain GMT.
Authority: Nautical Almanac; Bowditch (Pub. No. 9), zone time
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