SEASONAL PATTERNS: What Causes the 4 Seasons?

Seasonal Patterns

Last Updated: Dec 31, 2018

What causes seasonal patterns?

Earth Tilt

Because the Earth is tilted on its axis, it’s the main reason why we have seasons. As the Earth revolves around the sun, the hemisphere that’s tilted towards the sun receives most sunlight.

When it receives more sunlight due to the tilt, this is summer time. For the hemisphere that’s tilted away from the sun, it receives less sunlight and has shorter days.

As a result, it becomes colder and this is the winter season. At the North Pole, is possible to have 24-hour days in darkness because of the tilt of the Earth.

At the equator, it’s exposed to sunlight more often. This is why is much hotter at the equator year-round. Because it is hotter for longer periods of time, there is less difference between seasons.

Summer solstice in the northern hemisphere

Summer Solstice

The Earth has an imaginary line through the center of Earth. The Earth’s axis goes through our geographic poles. Imagine sticking a pencil through Earth from pole-to-pole. Then, twist your hand at about 23.5 degrees.

Our seasons depend on how the Earth is tilted and oriented with the sun. For example, when the Earth is tilted towards the sun, it’s summer in the northern hemisphere.

When the Earth’s poles has its maximum tilt toward the Sun, this is the summer solstice. It occurs usually mid-June in the northern hemisphere. But at the outer side of the axis, it’s winter.

As you can see in the diagram, the northern hemisphere takes in most of the sun’s solar radiation.

Winter solstice in the northern hemisphere

Winter Solstice

But solstice happens twice every year. Once again, it occurs in the southern hemisphere at the opposite time of the year.

But when the Earth revolves around the sun, now the Earth is tilted in reverse. So the southern hemisphere is summer because the Earth is tilted towards the sun.

Countries like Australia in December are tilted toward the sun, so it’s now summer solstice in the Southern hemisphere.

This happens usually at the end of December. And at the opposite end of Earth, North America is tilted away from the sun so it’s winter solstice there.

Why is the north and south pole so cold?

Earth Rotation

At the equator, the sun hits the Earth directly. Whereas at the poles, the sun’s rays can barely touch it.

More specifically, it’s not because the equator is closer to the sun. But it’s because the sun is directly shining on the equator.

This is why we have the warmest ecosystems on Earth at the equator like tropical rain forests and deserts. For example, the Koppen climate classification system lists tropical climates sustaining temperatures of 18 °C or higher.

The north and south pole hardly receive any heat from the sun’s rays. This creates the coldest places on Earth like tundra and polar deserts.

Earth’s 4 seasonal patterns

Not only is the Earth revolving around the sun, but the Earth is rotating on its axis. In fact, it takes about 24 hours to fully spin in a circle.

When you’re facing the sun, it’s daytime. But when you’re on the part of the Earth that’s away from the sun, it’s night time. This day-night boundary is the terminator line.

But seasons occur because of the tilt of the Earth. When the northern hemisphere is tilted towards the sun, it receives more of the sun’s rays and it’s summer.

But when the Earth revolves around the sun, the northern hemisphere is tilted away from the sun and it’s winter.

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