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Day, night and the four seasons

Tutor: Katherine

Day, night and the four seasons

In a nutshell

When parts of the Earth face the Sun it is daytime. When they are in shadow, it is nighttime. One full day is $24\ hours$​. The Earth rotates on its axis as it orbits around the Sun which causes the seasons. When the North Pole is tilted towards the Sun, the northern hemisphere in summer and when it is tilted away, it is in winter.

Definitions

Definition

Orbit
The curved path which objects move around larger celestial objects in space
Northern hemisphere
North half of the Earth
Southern hemisphere
South half of the Earth
North/South Pole
Northern or southern points of the line which the Earth rotates upon
Axis
An imaginary line where the Earth appears to rotate around

Day and night

Day is when the Sun appears in the sky and night is when it is not. It takes the Earth $24\ hours$​ to complete one full rotation, which is how one full day (day and night) is defined.

One half of the Earth is always facing the Sun and one half is always in shadow. As the Earth rotates, different parts of the Earth face the Sun, which is daytime. Other parts will not face the Sun, which is nighttime.

The year and seasons

The Earth orbits around the Sun and one full orbit takes $365\ days$​, which is one year. Over the course of a year, the seasons (winter, spring, summer and autumn) occur. They happen depending on if the Earth is tilting towards or away from the Sun.

This tilt means the North and South Pole are actually at an angle if you were to draw a vertical line through the Earth. In other words, the Earth spins on its axis.

 1 Equator 2 Earth's axis 3 Day time 4 Night time 5 Sun rays

When the northern hemisphere is in winter, the North Pole is tilting away from the Sun. This means the southern hemisphere is in summer, as the South Pole is tilting towards the Sun.

Six months later, when the Earth has completed half of its orbit, the North Pole will now tilt towards the Sun. This means the northern hemisphere is in summer and southern hemisphere will be in winter. In between are spring and autumn.

 1 Winter northern hemisphere 2 Autumn northern hemisphere 3 Summer northern hemisphere 4 Spring northern hemisphere

The Sun in the sky

The Sun appears to move in the sky, but it is actually the Earth rotating that causes this impression. The Sun rises in the east, and sets in the west. This is due to the direction in which the Earth is rotating.

During the summer, the Sun also appears higher in the sky  This is because the Earth is rotating on its axis. During the summer in the UK, the North Pole will be tilted towards the Sun and in the winter it will be tilted away.

 1 East 2 West 3 Summer 4 Winter 5 Sunrise 6 Sunset

The stars in the sky

At nighttime, the stars also appear to move, due to the Earth's rotation. During different seasons, the stars in the sky will change. This is because the Earth is now at a different point in its journey around the Sun. You are actually seeing a whole new set of stars!