September equinox

The September equinox happens when the sun is exactly above the equator, which is a pretend line in the middle of the Earth that separates the north from the south. This happens twice a year: once in September and again in March.

During the September equinox, daytime and nighttime are the same length all over the world. This means that if you drew a line right down the middle of the Earth, one half would be in daytime and the other half would be in nighttime.

The reason for this is that as the Earth orbits around the sun, it is tilted on its axis. This tilt is why we have seasons and why some parts of the world are hotter or colder than others. When one half of the Earth is tilted towards the sun, it is summer there. When it's tilted away from the sun, it's winter.

But during September (and March), the tilt is just right so that the sun shines directly on the equator. This is why it's called the equinox, which means "equal night" in Latin. And that's pretty cool!