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Anabasis wrote:

> I computed LAN= 12h 9m 42s by the equation of time method. What am I doing
> wrong?

Making your life more complicated than it needs to be ;-)  Forget the
equation of time at 12 hour intervals on the daily pages of the NA.  Quoting
Susan P. Howell from Practical Celestial Navigation, "A more exact way of
establishing the time of LAN is the find the hour, minute and second when
the Sun has its GHA equal to you longitude."

As she uses an example, I'll paraphrase.  Look at the GHA column for the
body of interest (Greenwich date and UT). Locate GHA's that bracket your
longitude (AP or known position). To find out how far you should
interpolate, subtract the GHA or the smaller UT hour from your longitude.

Convert the angular distance from arc to time.  Add that difference in time
to the UT used and convert to zone time. (Use the nominal 15d per hour
for the Sun per the NA tables.)  If you want to get crazy (not worth the
effort in the real world unless you are working from a known land position
or calibrating against a GPS), note the change in difference in GHA over a
24 hour to 48 hour period on the same daily page and divide by 24 or 48
respectively to get the actual rate of GHA change per hour. Use that to
convert arc to time on your $10 calculator.

Bill


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