Humans are diurnal creatures, which means that we are active during the day and sleep at night. Sunlight hours are when we work, play, and eat, and when the sun sets, we get ready for sleep. This divide is one of the most important aspects of our life, but have you ever really thought of why it happens?

　　The division of day and night is due to the rotation of the Earth. The Earth spins on an axis that goes from the North Pole to the South Pole. The world rotates eastwards on this axis and this is why the Sun appears to rise in the east and set in the west, though in reality it is the Earth that is moving around the Sun.

It takes about 24 hours for the globe to make a full rotation, during which time the entire Earth will experience a full day while that area is facing the Sun, and night when it is facing away from the Sun.

　　Of course, as you are probably well aware, the duration of daytime and nighttime are not equal. This is because of the Earth's axial tilt, which currently is 23.44°. This tilt changes throughout the year. When the North Pole is tilted towards the Sun, the Northern Hemisphere experiences summer along with more daylight hours, while the Southern Hemisphere experiences winter and shorter days.

What's more, the length of the day will vary depending on where you are in relation to the equator. In June, July, and August, the sun never sets in regions north of the Arctic Circle. As you can imagine, that can make it difficult to sleep sometimes.