Here's why:
* Latitude 23.5 degrees represents the Tropic of Cancer (North) and the Tropic of Capricorn (South).
* Solstices are the points in Earth's orbit when the sun's rays hit the Earth at the most extreme angles.
* Summer Solstice (around June 21st): The sun's rays hit the Tropic of Cancer at a 90-degree angle, causing the Northern Hemisphere to experience its longest day of the year.
* Winter Solstice (around December 21st): The sun's rays hit the Tropic of Capricorn at a 90-degree angle, causing the Southern Hemisphere to experience its longest day of the year.
Therefore, the sun's rays strike latitude 23.5 degrees at a 90-degree angle only twice a year, during the solstices.
