What Are the Four Seasons, and What Causes Them?

How does the same plant change through the year?

A plant is a useful way to notice a season, because changes in daylight, temperature and rainfall affect how it grows. The pictures below follow the same tree through one year. They show a common pattern, but not every South African plant changes in exactly the same way.

What causes the seasons?

Consider a spinning ball leaning slightly to one side while it travels in a large circle around a lamp. The ball represents Earth, and the lamp represents the Sun.

Earth spins once roughly every 24 hours, giving us day and night. At the same time, it travels around the Sun, completing one orbit in about 365¼ days. Earth’s axis, the invisible line through the North and South Poles, leans by about 23.5 degrees.

That lean keeps pointing in almost the same direction as Earth travels. Earth does not rock backwards and forwards every few months. The changing seasons happen because our leaning planet moves to a different part of its path around the Sun.

What does “more direct sunlight” mean?

The same amount of sunlight can produce different warming depending on the angle at which it reaches the ground.

What happens during spring?

Spring is the transition from winter to summer. In South Africa, we commonly call September, October and November the spring months. The Sun appears higher in the sky, daylight lasts longer and temperatures generally begin rising.

Plants respond to the changing light, warmth and available water. New leaves and flowers may appear, insects become more active and many animals enter important feeding or breeding periods.

Spring does not begin because something suddenly changes on 1 September. South Africa uses 1 September as a familiar Spring Day, but the increase in daylight and warmth has already been developing gradually. The astronomical spring equinox normally occurs around 22 or 23 September.

What happens during summer?

Summer is the warmest part of the year. South Africa commonly groups December, January and February as summer. During this period, the Southern Hemisphere is leaning more towards the Sun.

The sunlight is more direct, the Sun follows a higher path across the sky and daylight lasts longer. These conditions allow the land and air to gain more heat. Around 21 or 22 December, the Southern Hemisphere reaches its summer solstice, the longest day and shortest night of the year.

Much of South Africa receives most of its rain during the warmer months, often through afternoon thunderstorms. The Western Cape is an important exception because it has a Mediterranean-type climate and receives more of its rain during winter.

What happens during autumn?

Autumn is the transition from summer to winter. In South Africa, March, April and May are commonly described as the autumn months. Daylight becomes shorter, the Sun follows a lower path and temperatures begin cooling.

Some plants slow their growth. Certain trees break down the green colour in their leaves, revealing yellow, orange or red colours before the leaves fall. Dropping leaves can help a tree reduce water loss and survive a colder or drier period.

South African autumn does not look the same everywhere. Coastal areas may remain mild, evergreen indigenous plants can stay green, and warmer northern areas may show less dramatic leaf colour than colder inland locations.

What happens during winter?

Winter is the coolest part of the year. South Africa commonly groups June, July and August as winter. The Southern Hemisphere is leaning more away from the Sun, so our sunlight is less direct and our daylight hours are shorter.

Around 20 or 21 June, we reach the winter solstice, the shortest day and longest night of the year in the Southern Hemisphere. After that day, daylight slowly begins increasing again, even though the coldest weather may still arrive later because land, air and oceans take time to warm.

Winter does not automatically mean snow. Many South African places experience dry, sunny winter days and cold nights. Snow is mostly limited to high mountain areas and occasional cold events in suitable regions.

Why is South Africa’s summer America’s or Europe’s winter?

Earth is divided into two halves by the equator: the Northern Hemisphere and the Southern Hemisphere. When the Southern Hemisphere leans more towards the Sun, the Northern Hemisphere leans more away from it.

That is why South Africa can enjoy summer in December while countries such as the United Kingdom, Canada and much of the United States experience winter. Six months later, the situation is reversed.

Places close to the equator receive relatively direct sunlight throughout the year. Their year may be described more clearly by wet and dry seasons than by four strongly different temperature seasons.

Are seasons caused by Earth moving closer to the Sun?

No. Earth’s path is not a perfect circle, so its distance from the Sun changes slightly. But that distance change does not cause summer and winter.

The strongest proof is simple: both hemispheres are almost the same distance from the Sun at any moment, yet they experience opposite seasons. When South Africa has summer, the Northern Hemisphere has winter.

In fact, Earth is usually closest to the Sun in early January, during Southern Hemisphere summer but Northern Hemisphere winter. The angle of sunlight and the length of the day are the main causes of our seasons.

When does each season officially begin?

You may hear two different answers because people use two systems.

Neither system changes what Earth is doing. They are simply two ways of placing names and dates around a gradual, continuous journey.

A few useful questions the seasons