What is the first day of winter in the southern hemisphere?

Every year, weather forecasters welcome the arrival of winter on the first of December—while others contend that the winter really begins a few weeks later with the solstice, which falls on December 20, 21, or 22. So who is right about when the seasons begin and end?

It depends on why you’re asking. Seasons are defined in two ways: astronomical seasons, which are based on Earth’s position as it rotates around the sun, and meteorological seasons, which are based on annual temperature cycles. Both divide the year into spring, summer, fall, and winter—yet with slightly different start and end dates for each. Here’s what they mean and how to tell them apart.

Astronomical seasons

People have always looked to the skies to determine the season. Ancient Rome was the first to officially mark those seasons with the introduction of the Julian calendar. Back then, the seasons began on different days than the modern era because of discrepancies with the Gregorian calendar used primarily today. Now, the start of each astronomical season is marked by either an equinox or a solstice.

Equinoxes are when Earth’s day is split almost in half. They occur every six months in the spring and fall, when Earth’s orbit and its axial tilt combine so that the sun sits directly above the Equator. On an equinox, roughly half the planet is light while the other half is dark. As the new season progresses, the sun’s position continues to change—and, depending which hemisphere you live in, the days will get progressively lighter or darker until the arrival of the solstice.

Solstices mark the brightest and darkest days of the year. They are also driven by Earth’s tilt and mark the beginning of astronomical summer and winter. When the Northern Hemisphere is tilted toward the sun, it is brighter and feels like summer—while, at the same time, the Southern Hemisphere is tilted away from the sun, plunging it into a dark winter.

But this method of measuring the seasons presents some challenges. The solar year is approximately 365.2422 Earth days long, making it impossible for any calendar to perfectly sync with Earth’s rotation around the sun. As a result, astronomical seasons start on slightly different days and times each year—making it difficult to keep the climate statistics that are used in agriculture, commerce, and more. That’s why weather forecasters and climatologists turned to meteorological seasons instead.

Meteorological seasons

Since at least the 18th century, scientists have sought better methods of predicting growing seasons and other weather phenomena. Over time, that gave rise to the concept of meteorological seasons, which are more closely aligned with both annual temperatures and the civil calendar.

Meteorological seasons are far simpler than astronomical seasons. They divide the calendar year into four seasons that each last exactly three months and are based on the annual temperature cycle. Winter takes place during the coldest three months of the year, summer in the hottest three months, and spring and fall mark the remaining transition months.

In the Northern Hemisphere, that means the start date for each season is March 1 (spring), June 1 (summer), September 1 (fall), and December 1 (winter). In the Southern Hemisphere, the seasons are reversed; spring begins in September, summer in December, fall in March, and winter in June.

The consistency of meteorological seasons allows meteorologists to make the complex statistical calculations necessary to make predictions and compare seasons to one another. “Dealing with whole-month chunks of data rather than fractions of months was more economical and made more sense,” climatologist Derek Arndt told the Washington Post in 2014. “We organize our lives more around months than astronomical seasons, so our information follows suit.”

So when is the first day of winter? It isn’t December 1 or the winter solstice—it’s both.

A season is a period of the year that is distinguished by special climate conditions. The four seasons—spring, summer, fall, and winter—follow one another regularly. Each has its own light, temperature, and weather patterns that repeat yearly.

In the Northern Hemisphere, winter generally begins on December 21 or 22. This is the winter solstice, the day of the year with the shortest period of daylight. Summer begins on June 20 or 21, the summer solstice, which has the most daylight of any day in the year. Spring and fall, or autumn, begin on equinoxes, days that have equal amounts of daylight and darkness. The vernal, or spring, equinox falls on March 20 or 21, and the autumnal equinox is on September 22 or 23.

The seasons in the Northern Hemisphere are the opposite of those in the Southern Hemisphere. This means that in Argentina and Australia, winter begins in June. The winter solstice in the Southern Hemisphere is June 20 or 21, while the summer solstice, the longest day of the year, is December 21 or 22.

Seasons occur because Earth is tilted on its axis relative to the orbital plane, the invisible, flat disc where most objects in the solar system orbit the sun. Earth’s axis is an invisible line that runs through its center, from pole to pole. Earth rotates around its axis.

In June, when the Northern Hemisphere is tilted toward the sun, the sun’s rays hit it for a greater part of the day than in winter. This means it gets more hours of daylight. In December, when the Northern Hemisphere is tilted away from the sun, with fewer hours of daylight.

Seasons have an enormous influence on vegetation and plant growth. Winter typically has cold weather, little daylight, and limited plant growth. In spring, plants sprout, tree leaves unfurl, and flowers blossom. Summer is the warmest time of the year and has the most daylight, so plants grow quickly. In autumn, temperatures drop, and many trees lose their leaves.

The four-season year is typical only in the mid-latitudes. The mid-latitudes are places that are neither near the poles nor near the Equator. The farther north you go, the bigger the differences in the seasons. Helsinki, Finland, sees 18.5 hours of daylight in the middle of June. In mid-December, however, it is light for less than 6 hours. Athens, Greece, in southern Europe, has a smaller variation. It has 14.5 hours of daylight in June and 9.5 hours in December.

Places near the Equator experience little seasonal variation. They have about the same amount of daylight and darkness throughout the year. These places remain warm year-round. Near the Equator, regions typically have alternating rainy and dry seasons.

Polar regions experience seasonal variation, although they are generally colder than other places on Earth. Near the poles, the amount of daylight changes dramatically between summer and winter. In Barrow, Alaska, the northernmost city in the U.S., it stays light all day long between mid-May and early August. The city is in total darkness between mid-November and January.

The first day of winter in the Northern Hemisphere is in December; south of the equator, it is in June. Find out exactly when the winter season starts.

In the temperate and polar zones, winter is the cold season.

©iStockphoto.com/standret

Dec 6: Almost 90% of world's population in nighttime

Winter Dates for 2022/2023

According to the astronomical definition, winter begins with the winter solstice. In the Northern Hemisphere, it's the December solstice; south of the equator, it is the solstice in June.

What is a solstice?

Solstices and equinoxes in your city

Alternative Winter Start Dates

Meteorologists use a different method of defining the first day of winter. And, in some countries, the beginning of the seasons is determined by average temperatures rather than fixed dates or astronomical events.

Meteorological and other seasons definitions

Days Get Longer During Winter

Astronomical winter begins at the winter solstice, which is the shortest day of the year. This means days get longer during winter—very slowly at first, but at ever-larger daily intervals as the March equinox approaches, heralding the start of spring.

Locations closer to the poles experience larger differences in day length throughout the year, so winter days are shorter there. In Toronto, the shortest day is just under 8 hours and 56 minutes long; in Miami, roughly 2000 kilometers or 1200 miles farther south, it lasts about 10 hours and 32 minutes.

Places within the polar circles experience polar night during all or part of the winter season when the Sun does not rise at all.

Earliest sunset is not on the shortest day

Earth's orientation at the December solstice

© timeanddate.com

Longer Days, but Falling Temperatures

Although daylight hours increase during the winter months, temperatures continue to fall in most regions. This is because it takes time for Earth to warm up, an effect known as seasonal lag.

Winter Traditions and Folklore

The start of winter and the winter solstice are celebrated in cultures and religions around the world with various traditions, holidays, and festivals.

Winter festivals: Christmas, Juul, and Saturnalia

Winter Months

In the Northern Hemisphere, astronomical and meteorological winter runs from December to March. South of the equator, it starts in June and ends in September. Read more about the history and meaning of the winter months:

Northern winter months

December | January | February | March

Southern winter months

June | July | August | September

How Long Is Winter?

The Earth does not move at a constant speed in its elliptical orbit, so the seasons are not of equal length. On average, winter lasts for 89.0 days in the Northern Hemisphere and 93.6 days in the Southern Hemisphere.

Average season lengths:

Topics: Astronomy, Seasons, December, June, Sun, Solstice