Day, night and shadow lengths
The spinning Earth gives us day, night and changing shadows.
Day and night
The Earth rotates on its axis once every 24 hours. The side facing the Sun has day. The side facing away has night. As the Earth turns, the Sun seems to move across the sky.
When it is midday in Dhaka, it is the middle of the night on the opposite side of the Earth, in places such as Mexico.
The Sun’s path
The Sun appears to rise in the east, climb high at midday and set in the west. It is the Earth that moves, not the Sun.
The Sun rises in exactly the east and sets in exactly the west only around 21 March and 23 September.
Shadows during the day
In the morning the Sun is low, so shadows are long and point west. At midday the Sun is high, so shadows are short. In the evening, shadows are long again and point east.
Your own shadow can help you find directions: in the morning, your shadow points roughly west.
Measuring shadows
Use a shadow stick in a sunny place. Measure its shadow every hour and record the results in a table. Draw a graph: it shows the shadow is shortest around midday.
The shortest shadow of the day happens at “solar noon”, when the Sun is highest. In Dhaka this is close to 12 o’clock.
What I learnt
- I can explain day and night using the rotation of the Earth.
- I know how and why shadows change during the day.