The Sun's rays hit the Earth most directly at a 90 degree angle. This happens when the Sun is directly overhead, also known as solar noon.

However, this only occurs at specific locations on Earth depending on the time of year and latitude:

* Equator: The Sun is directly overhead (90 degree angle) at the equator twice a year during the equinoxes (around March 20th and September 23rd).

* Tropics: The Sun is directly overhead at some point during the year within the Tropics of Cancer and Capricorn (between 23.5 degrees North and 23.5 degrees South latitude).

* Other latitudes: At latitudes outside the tropics, the Sun never reaches a 90 degree angle.

It's important to note that the angle of the Sun's rays changes throughout the day and year, affecting the intensity of sunlight and the length of shadows.