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The Relationship Between Time and Longitude, Continued
Converting Arc
The following table shows how to convert arc to time.
to Time
Step
Action
Example: Convert
215°24' 45" of arc to
time.
1.
Divide the degrees by 15 to obtain
215° ÷ 15 = 14h20m
hours, and multiply the remainder
by 4 to obtain minutes of time.
2.
Divide the minutes of arc by 15 to
24' ÷ 15 = lm36s
obtain minutes of time, and
( r e m a i n d e r 5 °
4 = 2 0 m )
multiply the remainder by 4 to
obtain seconds of time.
3.
4.
Divide the seconds of arc by 15 to
45" ÷ 15 =
3s
obtain seconds of time.
( r e m a i n d e r 9 '
4 = 3 6 s )
Add hours, minutes, and seconds.
Answer: 14h21m39s
Finding ZD
To calculate the ZD for a given position, follow the steps as shown below.
Step
Action
1.
Divide the longitude of the position by 15°.
2.
If the remainder is less than 7°30', the whole number
quotient from step 1 equals the ZD.
3.
If the remainder is more than 7°30', the ZD is one more
than the whole number of the quotient.
Example 1:
135° W ÷ 15 = 9 The longitude is west, so the ZD = +9.
Example 2:
062° W ÷ 15 = 4 with a remainder of 2. The remainder is
LESS THAN 7°30" and the longitude is west, so the ZD = +4.
5-9
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