Summer and Winter Solstice

North Carolina experiences all four seasons (spring, summer, fall, and winter) and we have the tilt of the Earth to thank for this! In the Northern Hemisphere summer, for example, the Earth is tilted towards the sun, meaning that the Northern Hemisphere receives more incoming radiation (and solar heating) than the Southern Hemisphere, which is tilted away from the sun. The date at which the Earth’s tilt points most directly toward the Sun is called the summer solstice, and, conversely, the date at the Earth’s tilt points most directly away the Sun is called the winter solstice. In the Northern Hemisphere, these are the longest and shortest days of the year, respectively. This means that in June, July, and August, when we see our summer heat in North Carolina, the Southern Hemisphere is actually experiencing winter! When we experience winter in the Northern Hemisphere (December, January, and February), it’s because the Northern Hemisphere is tilted away from the sun and receives less radiation. During these months, the Southern Hemisphere experiences summer!

Diagram of seasons - Summer Solstice in June; Winter Solstice in December; Vernal Equinox in March; Autumnal Equinox in September
Title of the Earth and Northern Hemisphere Solstice Dates. Image from NOAA

Spring and Fall Equinox

During spring and fall, the earth is in a transition phase. What usually marks the occurrence of spring and fall astronomically is the equinox. The equinox occurs when the sun is directly focused on the earth’s equator and causes 12 hours of daytime hours and 12 hours of nighttime hours across the entire earth (in Latin, equinox means equal night).  There are two types of equinoxes that occur: the vernal and the autumnal. The vernal equinox marks the beginning of astronomical spring for the Northern Hemisphere and the beginning of astronomical fall for the Southern Hemisphere. As time passes, the Northern Hemisphere gradually receives more of the sun’s rays and also experiences longer daylight hours. The autumnal equinox marks the beginning of fall in the Northern Hemisphere and spring in the Southern Hemisphere. The Northern Hemisphere gradually receives less of the sun’s rays over time and also experiences less daylight hours. In addition to revolving around the sun, the earth rotates counter-clockwise on its own axis. This rotation allows us to experience day and night.

Climatologists usually use full months to represent the seasons.  Winter is considered December, January and February; spring is March through May; summer is June through August; and fall or autumn is September through November.