When the Earth takes one full lap around the sun, we call that a year. As you know, humans separate our year into 4 seasons: Spring, Summer, Fall, and Winter.

I found this great image that shows the Earth and the Sun during each season:

Figure 1. The Earth’s orbit around the sun.

Notice how the earth is tilted to one side. This tilt is the key to understanding how the sunlight is different for each hemisphere.

Take a look at the left and the right sides of Figure 1 above. On the right side is labeled “Summer Solstice,” and the left side is labeled “Winter Solstice.” These labels refer to the seasons we experience in the Northern hemisphere. As you can see, at the Summer Solstice, the North pole is tiled towards the sun: Figure 2

Figure 2. Earth (North pole) tilted towards the sun during a Summer Solstice.

And at the Winter Solstice, the North pole is tilted away from the sun: Figure 3

Figure 3. Earth (North pole) tilted away from the sun during a Winter Solstice.

Let’s think about our experience as residents of the Northern hemisphere: When are the days the longest? During the Summer! But what happens in the Southern hemisphere at the same time? Exactly the opposite, because while the North pole is tilted towards the Sun, the South pole is tilted away from the sun!

So how do we deal with the fact that each hemisphere is oriented oppositely We simply give the opposite season for the Southern hemisphere as we do for the Northern. So while we are enjoying the long days of Summer, the Australians (and everyone else below the equator) have the short days of winter.

Finally, we can think of every day in between the Solstices (both Summer and Winter) as a transition between one or the other. So while the Northern hemisphere gets the most sun exposure on the Summer Solstice, it gradually reduces over the course of 6 months until we reach the other side of the Sun, where it is now the Winter Solstice. When the transition is exactly halfway done, we call that an Equinox, where we mark the beginning of Spring or Fall. Compared to Figure 2 and 3, what do you think the Earth looks at the Equinox? Think about it, then check your answer with the resource I’ve provided below.

So with each passing day, we get a slightly different amount of sunlight in almost every part of the world. Can you think of a time and place where the sunlight is either all on, or all off for more than a day?

If you’d like to read more, here is a great resource, and the source for the figures as well: