It’s been said that, “time will pass and seasons will come and go.” But what causes these seasons to change, and why do we have seasons in the first place?
Some people assume that the Earth must be closer to the Sun in the summer, and further from the Sun in the winter, but this is not correct. In fact, in some areas, the exact opposite is true.
In reality, seasonal changes can be attributed to the tilt of Earth’s Axis. If you’re feeling confused, worry not! We’ll explore this process a bit more.
What is Earth’s Axis?
An axis is an imaginary line about which a body rotates. It runs through the center of an object. Many objects, from the smallest of particles to the largest of stars, have an axis. Each planet has a north and south pole. These points are where the the axis of rotation meets the surface.
Earth rotates around an axis as well. It takes approximately 24 hours for Earth to make one rotation, which is why we have 24 hours in a day.
Understanding What Causes Seasons
Some planets have axes that are almost completely perpendicular, or straight up and down without any tilt. In our solar system, we know that Mercury, Venus, and Jupiter fall into this category.
Earth’s axis, however, has what scientists call a tilt. In other words, the axis doesn’t stand up straight, but leans to one side. Earth’s tilt is about 23.5 degrees. It is thought that perhaps this tilt is the result of a massive impact event on Earth some 4.5 billion years ago. Many scientists believe this impact was so large, it not only titled Earth, but also led to the formation of our moon from debris that was blasted out into space.
Whatever the cause of the tilt, we know that it plays a crucial role in why we have seasons. As Earth orbits around the sun, its tilted axis always points in the same direction. This means that throughout the year, certain parts of Earth will receive the sun’s rays more directly.
Why Do We Have Seasons?
Our seasons are based on what part of the planet is getting more direct sunlight.
When the North Pole is pointing towards the sun, the Northern Hemisphere will experience summer, as the Sun’s rays hit that part of Earth more directly than any other time of the year. When this is happening, it is winter in the Southern Hemisphere.
The exact opposite is true when the South Pole is pointing the sun – it is summer in the Southern Hemisphere and winter in the Northern Hemisphere.
During the spring and fall, the sun shines pretty much equally on the Northern and Southern Hemispheres.
Earth’s orbit around the Sun is not a perfect circle, so it is true that the Earth’s distance from the Sun does change throughout the year. However, the Sun is so far away that these distance fluctuations don’t have much effect on our weather. If you want proof, when the Earth is closest to the Sun, it is winter in the Northern Hemisphere.
Solstices and Equinoxes
In the Northern Hemisphere, the summer solstice occurs at the moment the Earth’s tilt toward the Sun is at a maximum. This happens when the Sun is directly over the Tropic of Cancer, which is located at 23.5° latitude North. The summer solstice is the longest day of the year and considered to be the official start of summer.
The winter solstice, conversely, is the shortest day of the year. In the Northern Hemisphere, it occurs when the Sun is directly over the Tropic of Capricorn, which is located at 23.5° latitude South. The winter solstice falls around December 21st or 22nd, and marks the beginning of winter.
Equinoxes happen twice a year, signaling the first day of spring or the first day of fall. On these two dates, the Earth’s axis is tilted neither toward nor away from the sun. This results in relatively equal amounts of daylight and darkness at all latitudes.
Hopefully this has shed some light on why we have seasons. If you liked this post, click here to find more science articles from the Sporcle Blog. And remember to drop by Sporcle.com for thousands of quizzes and games on just about every topic you can image!