There are lots of different ways to measure or define a season. The solstices and equinoxes, in some cultures and countries, are used to mark the beginning of a season. However, it might not really mark how the temperature or climate is changing. Is December 21, the summer solstice, really the start of warm, summer weather here in Australia?

Numerous Aboriginal seasonal calendars, such as those of the Nyoongar in south-west Western Australia or the Yolngu in Arnhem land, have noted six seasons is more appropriate for the Australian climate. At its essence, a season really is just marking a period of climate in a location.

But why do we have seasons in the first place? Well, we have the Earth's tilt to thank for that. As of today, the Earth is tilted 23.44 degrees. However, the Earth's tilt does wobble a bit so it can range from 22.1 to 24.5 degrees. But tilted to what?

Our Solar System is a giant disc, and we call the imaginary line of that disc the ecliptic. All the planets lie on it and go around the Sun on it.

The tilt is the angle between how a planet spins (its rotational axis) with respect to how we go around the Sun (its orbital axis). If we spin essentially straight up and down with respect to how we go around the Sun, we'd have a tilt of 0 degrees. If we spin in the same direction we go around the Sun, we would tilt around 90 degrees, like we are on our side.

In our Solar System, the planets all have different tilts. Mercury has no tilt and Jupiter has a tiny one of only 3 degrees. Mars's tilt is about 25 degrees, making it very similar to the Earth.

Uranus has a tilt of almost 98 degrees, meaning it is like a ball on its side rolling around. All of these tilts make the seasons different on each planet.

As the Earth tilts, when it is the summer in a hemisphere, say 21 December for us here in the southern hemisphere, that means we are at maximum tilt towards the Sun. Therefore, we get more sunlight, which gives us longer days, and more heat, which warms us. At the same time though, it means the northern hemisphere is tilted away from the Sun, so less light, which means shorter days and less heat.

On the equinoxes, autumn and spring, the Earth's tilt is even, so both hemispheres get the same amount of light. It also means that for the most part, we have the same length of day as night, about 12 hours.

READ MORE SPACE NEWS:

We think the Earth's tilt is the same reason we have the Moon - a giant collision 4.5 billions years ago. We believe something about the size of Mars (but not Mars), crashed into the Earth, causing us to lose a lot of rock, which eventually turned into the Moon, and get our tilt.

So our seasons have nothing to do with being closer or further from the Sun, it is just what hemisphere is tilted more. And we have an ancient, giant collision to thank.