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    Re: USCG exam memories
    From: Jeremy C
    Date: 2010 Dec 27, 08:29 EST
    It gets worse Greg.  The new system to advance your license includes a large number of classes which included practical examination elements.  We now take two tests, one for 3rd mate, and the second for Chief mate.  The 3rd mate celestial navigation requires you to observe regular sun lines, LAN, and star lines among other things.  The "advanced" celestial navigation practical require you to shoot a upper transit of a body other than the sun and an Ex-meridian of the sun.
     
    You talk about the tables.  I was at my union school (Ft Lauderdale, FL) in the third week of June and we went to the beach and shot our ex-meridian of the sun.  It was well over 86 degrees Hs.  We got back to class and I flipped open Bowditch only to discover something:  If you look closely at the tables, when the zenith distance is too small (< 4 deg), the tables fall apart.  The teacher knew this would happen and had a USCG exam question for us to reduce because our shots were unable to be reduced using the ex-meridian method.  That was about the only thing that I learned in that class.
     
    My CM/Masters test had an ex-meridian of a LOWER transit to work out.  That was a fun one. 
     
    I agree that the whole process of ex-meridian is pretty pointless when you have an accurate timepiece.  It takes longer to do a ex-meridian than a standard reduction, when using tables for both.  I find it strange that ex-meridians are one of the things that IMO focuses on for the advanced navigation practical.
     
    One last thing, I never use the second table.  I find the altitude factor "a" from the first table and then used the formula C=(a*t^2)/60.  a is from the table, t is meridian angle in minutes of time.  C is your correction to Ha.
     
    Jeremy
     
    In a message dated 12/26/2010 2:05:29 A.M. Central Asia Standard Tim, gregrudzinski@yahoo.com writes:

    The strangest Nav exam question that I can remember involved the ex-meridian. This required table 29 and 30 lookups in Bowditch to correct an observed altitude near meridional passage to get the actual meridian altitude (Bowditch calls this reduction to meridian). Never used this method outside the exam room and felt that it was a curious antiquated celestial technique. Table 29 is entered with the nearest whole latitude and declination to get the one minute altitude rate of change(a). The one minute rate of change(a) and meridian angle(t) or minutes to transit are used to enter table 30 for the correction in minutes of arc to be added to the observation(Ho) to get an upper transit altitude. Table 30 covers observations made within 28 minutes of time either side of meridional passage.

    Greg Rudzinski
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