The December solstice is here. Here’s how it works and why it starts winter and summer at the same time.

earth winter summer solstice 21 december 2018 illustration google earth pro

An illustration of Earth at the December solstice in 2018.Google Earth Pro

  • The winter solstice of 2022 will occur on Wednesday, December 21 at 4:48 p.m. ET.

  • It is the winter solstice in the northern hemisphere, but the summer solstice in the southern hemisphere.

  • This is due to the tilted axis of the Earth as it revolves around the sun. This is why.

The December 2022 solstice will occur at 4:48 p.m. ET on Wednesday.

For people living in the Northern Hemisphere, it will be the shortest day of the year. It also signals the arrival of winter and a gradual advance into the spring season, the beginning of which is marked by an equinox.

For those in the Southern Hemisphere, it’s just the opposite: December’s solstice marks the beginning of summer when the days have reached their longest and brightest. This means that daylight hours will decrease and sunlight will weaken during the March equinox and up to the June solstice.

Two things drive this all-important seasonal shuffle: Earth’s tilted axis and the planet’s orbit around the sun.

How the December Solstice Works

The winter solstice is the point at which the sun is closest to the horizon throughout the day.

The Earth rotates on its axis once a day and revolves around the sun about once every 365 days.

The Earth’s axis is not perfectly perpendicular to its orbit around the Sun. It’s tilted about 23.45 degrees, meaning different parts of the world receive more or less sunlight depending on the time of year.

earth during december solstice summer winter tropic cancer capricorn tilt axis sunlight graphic insider shayanne gal

The Earth’s axis is tilted compared to its orbit around the Sun.Shayanne Gal/Business Insider

During the winter solstice, the northern hemisphere is tilted away from the sun, so the sun rises later and sets earlier, stays very close to the horizon, and countries to the north get the least amount of sunlight they’ll get all year.

For areas above the Arctic Circle, such as in Northern Canada and Scandinavian countries, the sun won’t even rise.

earth during december solstice summer winter tropic cancer capricorn tilt axis sunlight graphic insider shayanne gal

The Earth’s axis is tilted compared to its orbit around the Sun.Shayanne Gal/Business Insider

At the same time, the southern hemisphere of the Earth is tilted towards the sun.

That means the sun rises earlier, southern countries get the most light of the year and summer begins. If you are on the Tropic of Capricorn on Wednesday afternoon, a person standing outside has practically no shade because the sun is almost overhead.

In countries below the Arctic Circle, the sun does not set.

How the earth’s axis and orbit control the seasons

Our planet’s orbit is elliptical and its center of gravity is slightly offset from the sun.

This means that the time it takes to cycle through the seasons is not perfectly distributed:

earth equinoxes solstices sun light axial tilt seasons diagram graphics insider shayanne gal

How the Earth, its axial tilt and the Sun work to create solstices, equinoxes and seasons.Shayanne Gal/Business Insider

As the image above shows, it takes 89 days after the December solstice for Earth to reach the March equinox — that’s when the sun’s most direct rays have slipped back toward the equator. Another 92 days and 19 hours later, it’s the June solstice. At that time, the sun’s most direct rays reach the Tropic of Cancer, summer begins for the northern hemisphere, and winter begins for those south of the equator.

It then takes 93 days and 14 hours for the sun’s zenith to return to the equator and begin the September equinox, followed by 89 days and 19 hours to complete the cycle with the December solstice.

During each of these phases, certain parts of the Earth’s surface receive more sunlight and energy is stored or extracted from water sources, leading to seasonal temperatures and weather variations.

What the seasons look like from space

Some satellites fly in a geosynchronous orbit, meaning they orbit the Earth fast enough to hover over one spot on the planet.

This provides a great opportunity to photograph the Earth over the course of the year and see how the angle of the sun changes.

NASA’s Goddard Space Flight Center created the animation below using geosynchronous satellite imagery taken over Africa, and it clearly shows the seasonal progression.

This article was originally published December 21, 2022. Dave Mosher contributed to the previous version of this article.

Read the original article on Business Insider

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