The Earth rotates once a day about its own axis which runs from pole to pole. So for roughly half the day a place will be facing the Sun and in the light, and the rest of the time it will face away and experience night time. It rotates from West to East which is why for us we see the Sun rise in the East. The line that marks the difference between day and night moves along the equator at a speed of about 1,600 km/h (1,000 mph).

The Earth's axis tilts at an angle of a little under 23.5 degrees. So as it spins the top of the axis 'nods' at the Sun for six months and then away. This tilt is the main cause of the seasonal changes in temperature and weather. When the North Pole is tilting towards the Sun this means summer in the northern hemisphere and winter in the South. This is reversed during the other six months. This also means that the length of daylight and night time will vary at different times of the year, depending where a place is on the globe. Near the equator, day and night are of equal lengths. In the mid-latitudes, the pattern is one of long winter nights and short summer nights. Near the poles, day and night each last for almost six months.

Twice during the course of a year, on 21 or 22 June and 21 or 22 December, the axis tilts directly towards (or away from) the Sun. These are the solstices, when daylight is longest in one hemisphere, and shortest day in the other. Three months from each solstice the Earth's axis lies such that both poles are roughly the same distance from the Sun. These are the equinoxes when everywhere on Earth has approximately 12 hours of daylight and 12 hours of darkness. The vernal equinox occurs on 20 or 21 March and the autumn equinox on 22 or 23 September.