Day and Night

Day and night occur as the Earth rotates about its own axis so that one half is always lit by the Sun whilst the otherhalf is in darkness.

The length of daylight varies throughout the year. This is due to the inclination of the Earth’s axis. The Earth does not rotate about a vertical axis but is tilted at an angle of 23.5O and always points towards the star Polaris. The variations caused by this inclination also account for the seasons (see Seasons) and mean that, in Britain, the greatest length of daylight hours in midsummer can be as much as 18 hours, whereas the shortest in midwinter can be as little as six hours. These hours vary depending on latitude. For example, the further north from the equator you travel in summer (when the northern hemisphere is tilted towards the Sun), the longer the daylight hours, so there are times at the North Pole when the Sun does not ‘set’. Likewise in winter (when the northern hemisphere is tilted away from the Sun), there are times at the North Pole when the Sun never ‘rises’.

Not to scale

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