When do sun's rays strike latitude 23.5 degrees s at an angle of 90 degrees?

The sun's rays strike latitude 23.5 degrees south, also known as the Tropic of Capricorn, at an angle of 90 degrees during the December solstice, which occurs around December 21st each year. This is when the Southern Hemisphere is tilted toward the sun, resulting in the sun being directly overhead at this latitude.