Great Circle paths are used by radio amateurs to determine the proper direction to aim antennas. When the antenna is not moveable, the great circle direction will, at least, give the operator some sense of whether the antenna is pointing in the right direction.
The skip distance varies between night an day as well as variations due to sun spots. Knowing the distance also gives some indication of the expected success of a desired communication.
On a flat earth, the bearing from the other station would be simply the reciprocal of the bearing from the home station. Not so with a spherical earth. So the bearing from the other station is also provided.
The distance may be expressed in statute miles, nautical miles, or kilometers.
The GrCirc program has been designed for ease of use. Once a location has been entered into the program, it may be retained in a list for future runs. The current home location and destination are also retained for future use.
Here is a link to the GrCirc files - Updated 8/01/07 to Version 1.0
Microsoft, in their attempt to protect you against unknown sources of code now blocks programs not know to them. This protection has changed. As of this writing, in order to have both the program and the help features work, you must first download the .zip file to your machine, Then right click on the .zip file and select properties. At the bottom of the properties window, click Unblock. Then say "OK" to exit the properties window and open the .zip file. On the "File" menu (top left) select "Expand All" and follow the instructions to place the files wherever you want them. You may then discard the zip file.
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