On the northern summer solstice (around the 21st June each year), the Sun reaches its most northerly declination of +23.5 degrees.

This means that for an observer on the Tropic of Cancer in the Northern Hemisphere, the Sun will be directly overhead, and the northern summer solstice marks the longest day of the year (most hours of daylight). On the contrary, for an observer in the Southern Hemisphere, the northern summer solstice marks the shortest day of the year (least hours of daylight). The southern summer solstice occurs 6 months later, around 21 December.