What is the Summer Solstice?
The Summer Solstice is one of the 24 solar terms in the agricultural calendar, marking the official beginning of summer.
On the Summer Solstice, the Northern Hemisphere experiences the longest day and shortest night of the year. In Western astronomy, this day signifies the start of summer in the Northern Hemisphere and the start of winter in the Southern Hemisphere. According to the Eastern perspective, the Summer Solstice is the middle of summer, with the character "至" (Zhì) meaning "to reach the extreme point." On this day, the sun reaches its highest point in the northern sky at noon and gradually begins its return southward.
The Summer Solstice typically occurs between June 21 and 22 in the Gregorian calendar (after the Mangzhong solar term) and ends around July 6 to 8 (when the Xiaoshu solar term begins). In 2024, the Summer Solstice will fall on June 21, the day with the most sunlight of the year, approximately 1/4 minutes longer than 24 hours.
Why Does the Summer Solstice Have the Longest Day of the Year?
When the Summer Solstice begins, Earth is tilted 23.5 degrees on its axis. On June 21 (or sometimes June 20), the North Pole is tilted towards the sun the most. During this time, the Earth's northern half leans towards the sun to its maximum extent, while the South Pole is in darkness.
Earth is actually farthest from the sun in summer due to its elliptical orbit, which leads to variations in the distance between the Earth and the sun. This difference amounts to about three million miles (five million kilometers) and results in Earth receiving 7% more solar radiation than on average days.
Interesting Facts About Summer Solstice
Earth is farthest from the sun: Contrary to popular belief, Earth is not closest to the sun during the Summer Solstice. Instead, it is at its farthest point in the year, called the aphelion, which occurs a few weeks after the Summer Solstice.
Not Earth-exclusive: The Summer Solstice is not unique to Earth; it occurs on all planets in the solar system. Mars experiences its Summer Solstice a few days after Earth, while Uranus has a Summer Solstice every 84 years.
Not the hottest day of the year: Despite receiving the maximum amount of sunlight and radiation on the Summer Solstice, it is not necessarily the hottest day of the year. Typically, the hottest days in the Northern Hemisphere occur in July or August when continents and oceans warm up, resulting in higher temperatures, known as the "seasonal lag."