What makes the seasons change?



In school (US) I moved around a lot and I feel like I learned two separate theories on what makes seasons change: 1) the tilt of the Earth on it’s axis and 2) the distance of the Earth from the Sun during its yearly trip around. I understand that (1) is correct, but why does the slight tilt of the Earth make more of a difference than the actual distance from the Sun? And how is it possible that it’s difference is so significant that the Northern and Southern Hemispheres experience their seasons at different times?

In: Physics

Because the difference is large enough to make the sun above the horizon for longer periods during the summer, and plants and animals have evolved in a way to take advantage of that fact. The reason Northern and Southern Hemispheres experience it at different times is because whilst the sun is above the horizon longer in one Hemisphere it will be shorter in the other.

The slant changes how light strikes the Earth. The shallower the angle, the more energy is deflected instead of absorbed. Summer for whichever hemisphere is when that side is facing the sun as dead-on as possible, maximizing the absorption. Likewise, winter is when the hemisphere is canted, so more sunlight is deflected.

The Earths tilt make cause a difference between the amount of sunlight each hemisphere gets. Now the Northern hemisphere gets more sunlight than Southern and therefore it is summer in Northern hemisphere. When it is winter in Northern hemisphere, Southern hemisphere gets more sunlight. Sunlight causes differences in the temperatures and that causes seasons. The further away from Equator you are, the bigger the difference between summer and winter is. Also sea currents and winds affect seasons in different areas. For example Northern Europe would have colder winters without the Golf current in the Atlantic ocean.

The distance between Earth and Sun is smallest at Northern winter. That doesn’t effect the seasons much.


A simple way to consider it is to look at the relative size of the changes for each.Our orbit varies between 147 and 152 million km. That’s a difference of about 3% from the median.The length of a day in Paris (picked arbitrarily) varies between 8.3 hours and 16 hours, or very roughly 66% difference from the median. The length of the day is controlled by the tilt, which is why that’s the major factor.

Direct light from the sun is hotter than indirect light. During a hemisphere’s winter months, it is tilted away from the sun, so it sees less direct sunlight.

Here’s an experiment you can do at home. Take a laser pointer and point it at the center of a tennis ball, now tilt the tennis ball so its pointing slightly away from the laser pointer. Even though the same amount of light is hitting the ball, its spread over a greater area. This is what happens with the tilt of the earth and the suns rays