CHAPTER 36 – THE EARTH-SUN-MOON SYSTEM Days


Earth’s axis is an imaginary line that links the North and South poles. The Earth is tilted at an angle of 23.5° on its axis. When the Earth spins, half of the planet faces towards the Sun (in the light) and half faces away from the Sun (in the dark). This causes day and night on Earth. The Earth takes 24 hours to complete one full spin on its axis.


? TEST TUBE


3. Explain why one day on Earth is 24 hours. 4. Use a diagram to explain how night and day occur on Earth.


Seasons


The gravitational force of the Sun pulls the Earth into an elliptical (oval) orbit. Each orbit of the Earth around the Sun takes 365.25 days.


? TEST TUBE


5. A leap year (a year with one extra day) happens every four years. Explain why you think there is a leap year every four years.


A season is a period of the year when the weather and the number of hours of daylight change. Seasons on Earth change on or around the 21 March, June, September and December.


Seasons on Earth occur for two reasons: 1. The time taken for the Earth to travel around the Sun. 2. The angle of the Earth’s tilt on its axis stays the same during its orbit of the Sun (23.5°).


Spring


The northern hemisphere is facing towards the Sun


Autumn


The northern hemisphere is facing away from the Sun


23.5° Axis


:Fig. 36.5 The tilt of the Earth’s axis


Summer


Winter


Winter


Summer


Autumn


In summer, the tilt of the Earth means that Ireland spends more time in daylight then it does in the shadows


Spring :Fig. 36.6 How seasons occur due to the tilt of the Earth’s axis Elements of Science 349


In winter, the nights in Ireland are longer than the days due 


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