Explore the Seasons

As Earth travels around the sun every year, the North Pole points nearest to the sun around June 21. This marks the beginning of summer in the Northern Hemisphere. This day has the longest period of light and the shortest period of darkness of any day of the year. This day, on or around June 21, is called the summer solstice. On this day, the path the sun traces in the sky is at its highest point.

As Earth continues on its path around the sun, the number of daylight hours begins to decrease. By September 22, neither hemisphere is tilted toward the sun. On this day, the noon sun is directly overhead if you are standing on the equator. Every point on Earth will have 12 hours of sunlight and 12 hours of darkness. This day is called the autumnal equinox.

After the autumnal equinox, daylight hours continue to decrease in the Northern Hemisphere. The winter solstice, when the North Pole is pointed farthest from the sun, falls on or around December 21. It's the day of least sunlight and longest nighttime in the Northern Hemisphere. On this day, the sun's path is lowest in the sky.

Each day after the winter solstice, the sun's path creeps higher in the sky in the Northern Hemisphere. Days begin to get longer until March 21, the date of the vernal equinox. This day marks the beginning of spring in the Northern Hemisphere. As with the autumnal equinox, on this day the entire Earth experiences equal amounts of day and night.