Question

Where do the sun's rays strike Earth most directly and least directly?

Answer 1

Least-direct- inclination : latitude + `23.4^o`.
Most-direct-inclination : latitude-- `23.4^o`
See explanation.

Explanation:

In a period of 1 year, the angle of incidence of solar rays at latitude

`theta^o (N or S)` oscillates in `[theta-23.4, theta+23.4]^o`.

South or north of the equator,, it is direct over-head strike, twice in a

year, if the

latitude `<=` the obliquity ( tilt angle of the polar axis ) = `23.4^o`,

nearly.