Today, June 20, 2024 at 1:50 PM PST, is the summer solstice. This is the moment when the sun reaches its highest point in the Northern Hemisphere sky during the year, making it the longest day of the year in the Northern Hemisphere. However, if you’re in the Southern Hemisphere, today will be the shortest day of the year and the longest winter night.
The Sun’s position in the sky determines the length of day experienced by locations on Earth and depends on the Earth’s axial tilt and the Earth’s position in its orbit around the Sun. The Earth travels around the Sun on its orbital “trackway” at a speed of 66,620 miles per hour, but the tilt of the Earth’s axis has remained relatively constant over the centuries.
The North Pole points to Polaris and does not change appreciably over time. It takes 21,000 years for the Earth’s axial tilt to change by less than 2.5 degrees, so there is no noticeable change in axial tilt as the Earth orbits the Sun each year. Therefore, the Earth’s tilt does not cause seasons. The change in Earth’s annual seasons is the result of the Earth moving rapidly along its orbit while maintaining a relatively constant axial tilt.
In June, the North Pole faces the Sun, resulting in longer hours of daylight and hot, long summer weather in the Northern Hemisphere. Because the Earth is farther away from the Sun, the Northern Hemisphere is fortunate to experience relatively mild summers compared to the Southern Hemisphere.
During the Northern Hemisphere summer, the Earth moves away from the Sun and closer to aphelion. The Earth is closest to the Sun at perihelion, which occurs in early January. Summer temperatures are extremely high in Africa, Australia, and South America because the Earth is closer to the Sun, and the Southern Hemisphere’s days are longer and the Sun is higher in the sky. The Earth’s annual average temperature is higher in the Southern Hemisphere than in the Northern Hemisphere.
The seasons of the Earth, the spring equinoxes, the autumn equinoxes, and the winter solstices, occur as the Earth moves around the Sun. Starting tomorrow, the days will start to get shorter, so make the most of these long days. Have a great summer!
