The two days of the year when the sun is directly overhead at either 23.5 degrees north or south are called the solstices.

* Summer solstice: This occurs when the sun is directly overhead at 23.5 degrees north, marking the longest day of the year in the Northern Hemisphere.

* Winter solstice: This occurs when the sun is directly overhead at 23.5 degrees south, marking the shortest day of the year in the Northern Hemisphere.