June Solstice Brings Summer, Winter Seasons

The June solstice gives us the green light to welcome the summer season in the Northern Hemisphere and winter season in the Southern Hemisphere. This happens June 21, 2021, at 03:32 UTC, but for us in North America, that’s June 20 at 10:32 p.m. CDT (UTC-5).

In meteorology, summer begins on June 1. Yet, June 21 is perhaps the most widely recognized day when summer starts in the northern half of our planet and winter starts in the southern half. This astronomical beginning of the summer season and long-held, universal tradition of celebrating the solstice have allowed us to treasure this time of warmth and light.

Summer solstice explanation
During the solstices, Earth reaches a point where its tilt is at the greatest angle to the plane of its orbit, causing one hemisphere to receive more daylight than the other. Credits: NASA/Genna Duberstein

Along with marking the beginning of summer, this will also be the longest day of the year in the Northern Hemisphere. We will begin to see early dawns, long days, late sunsets, and short nights. On the solstice, our Sun will reach its highest point as it crosses the sky. Meanwhile, south of the equator, winter will begin!

The ancient cultures knew that the Sun’s path across the sky, length of daylight, and location of the sunrise and sunset all shifted in a regular way throughout the year. Additionally, people built monuments, like Stonehenge, to follow the Sun’s annual progress, to worship the Sun, and to predict its movements.

Earth's seasons
Click to view larger. Credit: NASA/Space Place

Today, we celebrate the solstice as an astronomical event caused by Earth’s tilt on its axis and its motion in orbit around the Sun.

Earth’s axis may be imagined as an imaginary pole going right through the center of our planet from “top” to “bottom.” Earth spins around this pole, making one complete turn each day. That is why we have day and night, and why every part of Earth’s surface gets some of each.

Earth doesn’t orbit upright; its axis is always tilted 23.5˚ with respect to the Sun-Earth line, which is why we have seasons. During the June solstice compared to any other time of the year, the north pole is tipped more directly toward the Sun, and the south pole is tipped more directly away from the Sun. As a result, all locations north of the equator see days longer than 12 hours and all locations south see days shorter than 12 hours.

Enjoy the new season – whichever half of the globe you’re in!

by Lance D. Davis

March Equinox Brings 2 Seasons: Spring, Autumn

The March equinox – also called the vernal equinox – is the beginning of the spring season in the Northern Hemisphere and autumn season in the Southern Hemisphere. It arrives on March 20, 2021, at 09:37 UTC (Coordinated Universal Time) or 4:37 a.m. CDT (Central Daylight Time).

illustration of the March (spring) and September (fall or autumn) equinoxes
An illustration of the March (spring) and September (fall or autumn) equinoxes. During the equinoxes, both hemispheres receive equal amounts of daylight. Credit: NASA/JPL-Caltech

During this equinox, the Sun will shine directly on the equator with nearly equal amounts of day and night, about 12 hours. Throughout the world, the Northern and Southern hemispheres will get equal amounts of daylight.

Click to view larger. Credit: NASA/Space Place

The equinoxes and solstices are caused by Earth’s tilt on its axis and ceaseless motion in orbit. Think of an equinox as happening on the imaginary dome of our sky, or as an event that happens in Earth’s orbit around the Sun.

In the Northern Hemisphere, the March equinox will bring us earlier sunrises, later sunsets, softer winds, and budding plants. With the opposite season, south of the equator, there will be later sunrises, earlier sunsets, chillier winds, and dry, falling leaves.

If you’re in the Northern Hemisphere, start watching the Sun as it sets just a bit farther north on the horizon each evening until the summer solstice. Also, enjoy the warmer weather and extended daylight!