During the summer solstice (June 21st or 22nd), the Sun shines directly at the Tropic of Cancer. Because of this, the Northern Hemisphere experiences its longest daylight hours during this time. In the regions close to the North Pole, the summer solstice results in a phenomenon called the "midnight sun", where the Sun stays above the horizon even at night. 

During the spring (March 20th or 21st) and autumn equinoxes (September 22nd or 23rd), the Sun shines directly at the planet's equator. During the equinoxes, the night and day are the same length everywhere on planet Earth. The equator receives its name from this phenomenon.

During the winter solstice (December 21st or 22nd), the Sun shines directly at the Tropic of Capricorn. The Southern Hemisphere experiences its longest daylight hours, whereas the Northern Hemisphere experiences its shortest daylight hours. Near the Arctic Circle, the Sun does not rise above the horizon, and the regions close to the North Pole experience a sunless period known as the polar night. 



The seasons are the result of two factors: 1) The fact that planet Earth rotates around a slanted axis, and 2) the fact that this axis remains the same throughout the year. Because of these two factors, in July the amount of sunlight is higher on the Northern Hemisphere, whereas in December the amount of sunlight is higher on the Southern Hemisphere.