As a proud pedant I have to take slight issue with bernardo. Points on the equator do not always experience 12 hours of day and 12 of night.
Only on each of the equinoxes does anywhere on the earth experience equal periods of light and darkness, and on these days all places on earth experience it. At other times during the year the length of night and day is not equal anywhere, but the difference in the length of night and day increases as one moves away from the equator. Points on the equator experience no more than about half an hour’s difference between the length of night and day all the year round. The further away from the equator you go, the greater that difference is.
In Britain the longest day (and night) is about 16 hours in duration. Scotland has longer days (in the summer) and nights (in the winter) than England because it is further from the equator .
This is all because the earth’s axis is tilted at an angle of 23.5 degrees to the plane of its orbit around the Sun. The North Pole is tilted towards the sun to a maximum degree on the Northern Hemisphere’s Midsummer Day (around 21st June) and away from it to a maximum on Midwinter Day (around 21st December). The equinoxes occur at the midway point between these two extremes.
The precise dates of the equinoxes vary from year to year but are around the 21st of March and 21st September.