What Are The Reasons For Seasons?

People often don't think much about the change of seasons. They know it happens almost everywhere, but they don't always stop to think about why we have seasons. The answer lies in astronomy and planetary science.

 

The tilt of Earth's axis in relation to its orbital plane is the main cause of the seasons. Think of the solar system's orbital plane as a flat plate. On the "surface" of the plate, most of the planets go around the Sun. Most planets' north and south poles don't point straight up and down from the plate. Instead, they point at an angle. This is especially true of Earth because its polar regions are tilted 23.5 degrees.

 

Earth may be tilted because of a big event in its history, which is likely what caused the Moon to form. During that time, an object (size of Mars) hit the young Earth pretty heavily. So, it tipped over on its side for a while until the system got back to normal. In the end, the Moon formed, and the tilt of the Earth settled to where it is now, at 23.5 degrees. It means that half of the planet is tilted away from the Sun for part of the year and the other half is tilted toward the Sun. 

 

Both hemispheres still get sunlight, but one gets it more directly when it's tilted toward the Sun in summer, and the other gets it less directly in winter (when it is tilted away). When the northern hemisphere is facing the Sun, it is summer in that part of the world. At the same time, there is less light in the south, so winter comes there. The solstices and equinoxes are mostly used to mark the start and end of seasons on calendars, but they have nothing to do with what makes the seasons.

 

There are four times of year: summer, fall, winter, and spring. Unless someone lives on the equator, the weather changes with each season. In general, spring and summer are warmer and cooler in autumn and winter. If you ask most people why it's cold in the winter and warm in the summer, they'll probably say that Earth must be closer to the Sun in the summer and farther away in the winter. It seems like this makes sense. After all, the heat from a fire gets stronger as you get closer to it. So why wouldn't being close to the Sun cause summer to be warm?

 

Even though this is a good observation, it leads to the wrong conclusion. This is why: Every year, Earth is farthest from the Sun in July and closest to it in December, so the "closeness" reason isn't right. Also, when it is summer in the northern hemisphere, it is winter in the southern hemisphere, and vice versa. If the seasons were only caused by how close we are to the Sun, it would be warm in both the northern and southern hemispheres at the same time. That doesn't happen. The tilt is the main reason why there are seasons. But there is something else to think about. 

 

The tilt of the Earth also makes it look like the Sun rises and sets in different parts of the sky at different times of the year. In the summer, the Sun is almost directly overhead at its highest point, and it is usually above the horizon (i.e., it is light out) for most of the day. This means that in the summer, the Sun will have more time to heat the Earth's surface, making it even hotter. In the winter, the surface has less time to heat up, so it's a bit cooler.

 

Most people can easily see this change in the sky's apparent positions. It's not hard to keep track of where the Sun is in the sky over the course of a year. In summer, it will be higher in the sky and rise and set at different times than in winter. Anyone can do this project, all they need is a rough drawing or picture of the east and west horizons in their area. Observers can look out and see the sunrise or sunset every day and mark where they are each day to get a full picture.

 

So, does it matter how close the Earth is to the Sun? Well, in a way, it does, but not in the way most people think. The Earth's path around the Sun isn't very elliptical. The distance between its closest point to the Sun and its farthest point is just over 3%. That isn't enough to cause big changes in the weather. It means that there is an average difference of a few degrees Celsius. The difference between summer and winter temperatures is much bigger than that. So, the amount of sunlight a planet gets is more important than how close it is to another star. That's why it's wrong to just assume that Earth is closer to the sun at some times of the year than at others. If you can picture how our planet tilts and moves around the Sun, it's easy to understand why we have seasons.

 

•    The tilt of Earth's axis is a big part of why we have seasons.

•    At that time, the part of the Earth that is tilted toward the Sun (north or south) gets more heat.

•    The seasons are not caused by how close the Earth is to the Sun.