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The angle of the Sun and the Earth's seasons. Image credit: NASA
You might wonder what causes the Earth’s seasons. This is due to the orbit of the Earth around the Sun and the tilt of its axis. The Earth does not receive sunlight in an evenly distributed manner. The way the planet is tilted, some rays hit straight on while others hit at an angle. This change in angle changes the intensity of the rays that touch the Earth.
The consequences of this are best explained by comparing countries at the Equator with other nations at Northern climates. You most likely know that countries near the Equator are very warm and have tropical climates. This is because the equator receives sunlight straight on. Southern countries also have their share of sunlight during a portion of sunlight also making them warm, but this diminishes as you get closer to the South Pole. However, at one point in the orbit of the Earth, the axis will tilt toward the sun. When that happens, the process reverses and nations above the equator get more sunlight than their southern neighbors. This is essentially what causes the changes in seasons.
When the axis starts to tilt away because of the Earth’s solar orbit, the Northern Hemisphere of the Earth begins to gradually get less sunlight than normal this creates the seasons of fall and winter. In the Southern hemisphere the opposite actually happens. It gets warmer creating the seasons of spring and summer. However some countries don’t experience spring as we know it in the North but have rainy seasons, but the same phenomenon causes the shifts in climate.
When the Earth’s axis starts to tilt toward the Sun the opposite happens and the North starts to get more sunlight it experiences spring and summer. The Southern hemisphere will start entering into fall and winter.
However, there are a lot of different factors other than just the amount of sunlight which can affect the actual length of the seasons. This has to do with Earth’s natural thermostat, the atmosphere. One of the atmosphere’s functions is to trap heat. This is what makes it possible for life to survive. We know from other planet like Mars and Mercury that a planet without a robust atmosphere will experience extreme swings in the temperatures. Another feature of the Earth that affects the seasons is the Oceans. Their currents which are powered by transfers of heat in the water help to also regulate temperatures. This is what helps to keep Northern continents like Europe warm enough to be habitable.
We have written many articles about the Earth seasons here on Universe Today. Here’s an article about why the Earth has seasons, and here’s an article about the Earth’s tilt.
You can learn more from this cool video that shows you how the seasons work.
We have recorded an entire episode of Astronomy Cast about the Earth. Listen to it here, Episode 51: Earth.
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