Solstice

A solstice is a special moment in the year when the Sun reaches its farthest point north or south in the sky. This happens because the Earth's tilt affects how directly sunlight reaches different parts of the planet. There are two solstices every year, usually around June 20–22 and December 20–22.

Many people around the world use the solstices to mark the changing of the seasons. The summer solstice, in June, is when some places get the most daylight of the year. The winter solstice, in December, is when they get the least daylight. These events have been important for cultures and traditions for thousands of years.

The word solstice comes from Latin, meaning “sun standing still,” because the Sun's apparent movement in the sky seems to pause for a little while during these days. Whether it is the longest day or the shortest day of the year, the solstice is a natural event that connects all of us to the rhythm of Earth and the Sun.

Etymology

The word solstice comes from the Latin words sol (meaning "sun") and sistere (meaning "to stand still"). This is because, during the solstices, the Sun's apparent path in the sky seems to pause or "stand still" before changing direction.

The term solstice entered the English language during the Middle English period. An older English word for this event was sunstead, which is rarely used today. Similar words exist in other Germanic languages, such as sólstaðr in Old Norse.

Definitions and frames of reference

For someone at the North Pole, the Sun appears highest in the sky once a year in June. This day is called the June solstice. For someone at the South Pole, the Sun is highest in December, called the December solstice. When it is summer at one pole, it is winter at the other.

The word "solstice" comes from Latin and means "sun-standing," because the Sun's apparent upward movement in the sky seems to pause and then reverse direction at these points. The Sun's path in the sky changes throughout the year due to Earth's tilt and its orbit around the Sun. The longest days happen around the summer solstice, and the shortest days around the winter solstice. Near the equator, these dates can shift slightly.

Relationship to seasons

Main article: Season

The seasons happen because Earth's axis is tilted about 23.44° relative to its path around the Sun. This tilt stays pointed in the same direction as Earth moves. For half the year, the Northern Hemisphere leans toward the Sun, and for the other half, the Southern Hemisphere does.

The two solstices are when this tilt has its biggest effect. At the June solstice, the Sun is directly overhead at latitude 23.44° north, called the Tropic of Cancer. At the December solstice, it is overhead at 23.44° south, the Tropic of Capricorn. During these times, areas inside the Arctic Circle can see the Sun all day, while areas inside the Antarctic Circle can have no sunlight at all.

Cultural aspects

The ancient Greeks were fascinated by the movements of the Sun and stars. They created the idea of the celestial sphere to help explain these movements. They used special terms to describe the times when the Sun reaches its farthest points in the sky, which we now call solstices.

Different cultures have different names for the solstices. In English, we often call them the summer solstice and winter solstice. Other cultures use names based on the months, like June solstice and December solstice, or names that show which half of the Earth the Sun is over, like Northern solstice and Southern solstice.

In East Asia, the solstices are part of a system of 24 solar terms that divide the year. The summer solstice is called Xiàzhì, and the winter solstice is called Dōngzhì. These terms mark the middle points of the seasons in their calendars.

Many cultures celebrate festivals around the times of the solstices. For example, Christmas is celebrated around the winter solstice in many places. In East Asia, the Dongzhi Festival happens on the winter solstice. Some people also celebrate Midsummer around the summer solstice. These festivals have been important for centuries, helping people mark the changing seasons and connect with nature.

In the constellations

The positions where the sun appears farthest north or south change over time as Earth moves. This shift moves the solstices through different star groups, called constellations.

Long ago, the northern solstice was in the constellation Leo. It later moved into Cancer, then Gemini, and today it is in Taurus. In the future, it will move into Aries. For the southern solstice, it used to be in Capricornus and is now moving toward Sagittarius, and will later enter Ophiuchus and Scorpius.