Exercise 5 Answers


Long. 35o,36’.5W. is in zone +2.

GMT   =  3h 35m 12s

Therefore ZT =  3h 35m 12s – 2h  = 1h 35m 12s.


Date = 5 July.  ZT = 3h 20m 30s

Long. 145o 15’.33E is in zone -10.

Therefore GMT =   3h 20m 30s – 10h

Therefore GD = 17h 20m 30s , 4 July.

Q.3.  Long. 158o, 2’.38E is in zone -11.

If GD = 2330, 3 July, then ZT = 2330 + 11h

Therefore ZT = 1030 4 July.


Long. 179o,59’.9E is in zone -12.

Therefore  ZT = GD + 12h

Therefore  ZT =  30. April 12h 01m + 12

Therefore  ZT = 1 May.  00h 01m


Long. 179o,59’.9W is in zone +12.

Therefore  ZT = GD – 12h

Therefore ZT =  30 April 11h 59m – 12

Therefore ZT = 29th. April 23h 59m


Both ships are positioned on the Equator and are 2 minutes of arc apart in terms of longitude.

Therefore the distance between the ships is 2 x 1855.32 m. = 3710.64 m.

Therefore, although the ships are in dates two days apart, they are only  approx. 3.7 geographical miles apart.

Click here to return to exercise 5

 A fuller explanation of this topic is given in the book ‘Astro Navigation Demystified’.

Useful Link:  The Sun as a time keeper.

Home:  www.astronavigationdemystified.com


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