Warmth? Yes, I remember that...a long time ago.
I assume you mean a Great Circle route
. The following is an edited quote found someplace on the web-
"The longest open sea great circle route that can be found on Earth runs from Pakistan to far eastern Russia- you'll sail out of the Indian Ocean
, under Cape Horn, and then all the way up the Pacific to Kamchatka, and...you will never bump into any significant land".
Here's the formula-
(For abreviation "DLo" stands for "Difference in Longitude between Beginning and End")
tan-1(sin(DLo) / (cos(Departure Latitude) x tan(Destination Latitude) - (sin(Departure Latitude) x cos(DLo))
If Azimuth calculated is negative add 180d to it.
If DLo is negative add 180 to it.
BE VERY CAREFUL WHEN USING THAT FORMULA!
Keep in mind which quadrant you'll initially be sailing or you'll end up going on a really
wrong angle. While it does solve the initial bearing problem it's a very tricky formula.
90-sin-1((sin(Destination Latitude) x sin(Departure Latitude) + cos(Destination Latitude) x cos(Departure Latitude) x cos(DLo))
Multiply the answer by 60 to get nautical miles
You can find these formulas in Bowditch Chapter 22 and Chapter 24 here;
already has a great circle plugin so you can just graphically pick departure and destination
points and it'll calculate the rest.