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east
North,South, East and West
The first sub-cardinal points are;
North East
South East
South West
North west
Each has a 45 degree separation from the two adjacent cardinal points and a 90 degree separation from each adjacent sub-cardinal point
You need special optics to focus infra-red.
The longer wavelengths do not focus at the same point (they are bent less by refraction).
Mirror optics are better.
No. It's not necessary.