I was solving an astronomy problem which said "south of due west." This could be interpreted in two different ways and I don't know which one is correct. Is 'south of' in that phrase an idiom? Or does it mean southwest?
Here is the full sentence:
The Sun rises north of due east and sets south of due west.
And the question is:
Which statement best describes the position of the Sun at sunrise and sunset as seen by an observer in northern hemisphere on June 21?
A. The Sun rises north of due east and sets north of due west.
B. The Sun rises south of due east and sets south of due west.
C. The Sun rises north of due east and sets south of due west.
D. The Sun rises south of due east and sets north of due west.
E. The Sun rises due east and sets due west.
Best Answer
Look at a compass rose.
Look at W for west. Now move 'southwards', which is anticlockwise1 in this case, from the point for west. Somewhere in that region is "south of due west". You would expect it to be no nearer south than it is to west, as that would be "west of due south". Conventions vary, but I would tend to interpret "south of due west" WSW, or west-south-west, which is actually due west of south west. It might mean south-west, of course, or if you use a traditional mariner's compass (the compass rose of which has another degree of subdivision, for a total of 32 points), it might mean "west by south" (WbS), the point between W and WSW. Unless you have a clear idea of what the conventions of the text are, it could be any point anticlockwise of west and not anticlockwise of south-west.
1: In this case it is anticlockwise; 'southwards' from east would be clockwise.