NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Andrew Seligman
Date: 2013 Sep 17, 08:11 -0700
I read the following example in Bowditch.
Why is the answer 11:59 and 55 seconds instead of 12:00 and 5 seconds?
Example 2: See Figure 1801. Determine the time of the
upper meridian passage of the Sun on April 16, 1995.
Figure 1801. The equation of time for April 16, 17, 18, 1995.
Solution: From Figure 1801, upper meridian passage
of the Sun on April 16, 1995, is given as 1200. The dividing
line between the values for upper and lower meridian
passage on April 16th indicates that the sign of the equation
of time changes between lower meridian passage and upper
meridian passage on this date; the question, therefore,
becomes: does it become positive or negative? Note that on
April 18, 1995, upper meridian passage is given as 1159,
indicating that on April 18, 1995, the equation of time is
positive. All values for the equation of time on the same side
of the dividing line as April 18th are positive. Therefore, the
equation of time for upper meridian passage of the Sun on
April 16, 1995 is (+) 00m05s. Upper meridian passage,
therefore, takes place at 11h59m55s.
To calculate latitude and longitude at LAN, the navigator
seldom requires the time of meridian passage to accuracies
greater than one minute. Therefore, use the time listed under
the “Mer. Pass.” column to estimate LANunless extraordinary
accuracy is required.
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