NavList:

   

Reply

Alistair-
 

 Your calculation itself is correct. I suspect the problem is simply that 
you've got conversions (hours/minutes/seconds or minutes/decimal) scrambled 
in there. I don't know why your book is saying to multiply by 60, multiple 
again by 15, then divide by 60. To me, that reduces down to simply 
multiplying by fifteen and that seems meaningless except for the fact that 
there are 15 degrees in one hour. That is, one day is 24 hours long, and that 
is one rotation of a globe marked into 360 degrees. So our globe rotates 15 
degrees per hour. (More or less!)

If you convert 9h 43m 30s into decimal hours, then multiply by fifteen, you'll 
get degrees in a degree/decimal format. Or you can tally up the hours and 
minutes into minutes or seconds format and use a different constant to 
calculate minutes into degrees, or seconds into degrees...whatever format 
suits your work.

Navigators still use degrees-minutes-decimal (DD.MM.mm) and, confusingly, 
degrees-minutes-seconds (DD.MM.SS), but they don't just use degrees-decimal 
(DD.dddd) even though some new international standards call for it, and that 
is a convenient way to eliminate a lot or calculation conversions.

I'd probably convert the hours, minutes, and seconds each into degrees, then 
add for a total. In this case:
9 hours (9 x 15)=          135.000 degrees;
43.5 minutes (43.5 x .25) = 10.875 degrees
                           =================
Total_____________________ 145.875 degrees.

The (43.5 x .25) comes from one minute being equal to 1/4 degree, which is 
just the result of dividing the 15 degrees in hour by, by the 60 minutes in 
that same hour. 15/60=.25

And I converted 43m30s into 43.5 minutes simply because 30 seconds is a 
convenient decimal portion of a minute.

   

Reply