ELi5: If seasons are due to the tilt of the earth and not the orbit around the sun, how do they occur on roughly the same days every year?

Question

Is it just coincidence that the 4 season begin and end at same point in the orbit around the sun?

In: Physics

Answer 1

It’s not coincidence. The tilt of the Earth means that sunlight is distributed differently over the Earth’s surface depending upon where in its orbital path it is. Opposite points in Earth’s orbit for summer and winter (ie. on different sides of the Sun) will have the sunlight more focused upon different hemispheres. This is the exact same reason why summer is at opposite times of the year for each hemisphere, so whilst it’s winter in January for the northern hemisphere, the southern hemisphere will be experiencing summer. Australians celebrate Christmas in the summer heat, often on the beach with barbecues going.

When people say that seasons are a result of Earth’s tilt rather than its orbit, they mean it’s not due to the fact that Earth is farther from the sun at certain points in its orbit than others (because the orbit is not a perfect circle, all orbits are elliptical to some degree). The distance between Earth’s closest and farthest points to the sun is much too small to make a noticeable difference, but it’s a common misconception that this is what causes seasons in people who have not had the real reason explained to them.