1. Why do we have night and day? Why do daylength’s change?
The Earth In Space
Why do we have night and day?
Why do daylength’s change?

2. Understanding Night and Day
Day and night is the absence or presence of sunlight shining on the surface of the globe!
It is caused by the spinning of the Earth on its axis
There are some strange things that you should be aware of, as well as what causes them!

3. The tilt of the Earth
The Earth spins on an axis. This is an imaginary line running through the middle of the Earth from North to South pole.
The important thing to note about the axis, is that it is tilted 23.5o from the vertical.
The tilt causes different daylengths depending on latitude on the Earth’s surface
The following animation demonstrates this. The coloured dots represent locations on the surface of the Earth that are in the same time zone.

4. 12 midnight

5. 2am

6. 3am

7. 4am

8. 6am

9. 8am

10. 10am

11. 12 noon

12. 2pm

13. 3pm

14. 4pm

15. 7pm

16. 9pm

17. 11pm

18. 12 midnight

19. 2am

20. 3am

21. 4am

22. 6am

23. 8am

24. 10am

25. 12 noon

26. 2pm

27. 3pm

28. 4pm

29. 7pm

30. 9pm

31. 11pm

32. 12 midnight

33. 2am

34. 3am

35. 4am

36. 6am

37. 8am

38. 10am

39. 12 noon

40. 2pm

41. 3pm

42. 4pm

43. 7pm

44. 9pm

45. 11pm

46. 12 midnight

47. 2am

48. 3am

49. 4am

50. 6am

51. 8am

52. 10am

53. 12 noon

54. 2pm

55. 3pm

56. 4pm

57. 7pm

58. 9pm

59. 11pm

60. So, what did you see?
The animation shows the Northern Hemisphere tilted towards the Sun. This is the position that it would be in on the Summer Solstice (21 June)
What do you notice about the blue circle?
What do you notice about the red circle?
What would happen to daylength if the green dot moved north?
What would happen to daylength if the green dot moved south?
How would the diagram be different if the Southern Hemisphere was tilted towards the Sun? When would this happen?
Click to run animation again

61. East and West
How does the Sun appear to move across the sky during the day?
NOON is when the Sun is HIGHEST in the sky.
Because the Earth SPINS, the Sun moves across the sky.
The Sun RISES in the EAST.
The Sun SETS in the WEST.

62. Length of Day
The Sun is at a higher angle in the sky in summer than in winter. This means the Sun is ABOVE THE HORIZON longer in summer than in winter. So, in summer, the days are longer and the nights are shorter, compared to winter.

63. Seasons
We have seen that on any given day, the amount of daylight varies between different locations on the Earth’s surface
However, even at a single location the length of daylight varies over a year
This is as a result of the Earth’s orbit around the Sun
This also results in the Seasons

64. Seasons (2)
You might expect that the reason it is warmer in the Summer is because we are closest to the Sun at this point
However, at Summer and Winter the Earth is at its two furthest points from the Sun
The Earth is nearest the Sun at the Spring equinox and the Autumn equinox

65. Terms to remember
Summer solstice – longest day ( approximately the 21 June)
Winter solstice – shortest day (approximately the 21 December)
Equinox – daytime is same length as night time.

66. The path of the Earth round the Sun
March
North and South getting equal amounts of sunlight
Spring in North. Autumn in South N S
March
North and South getting equal amounts of sunlight
Spring in North. Autumn in South N S N S N S N S N S N S
June
June N S
Northern hemisphere points towards the Sun
Longer days  Warmer
Summer in North! Winter in South N S
Northern hemisphere points towards the Sun
Longer days  Warmer
Summer in North! Winter in South
Northern hemisphere points away from the Sun
Shorter days  Colder
Winter in North. Summer in South
Northern hemisphere points away from the Sun
Shorter days  Colder
Winter in North. Summer in South N S N S N S N S N S N S N S N S N S N S
December
December
It takes days for Earth to orbit the Sun. Because of the .25 day, we add an extra day to our year every four years – a leap year.
North and South getting equal amounts of sunlight
Autumn in North. Spring in South
North and South getting equal amounts of sunlight
Autumn in North. Spring in South
October
October

67. Why is it summer when the northern hemisphere is tilted towards the Sun?
When the northern hemisphere is tilted towards the Sun, the Sun is at a higher angle in the sky and the Sun’s rays are less spread out. They have a greater heating effect.
In northern winter the Sun is at a lower angle in the sky because the northern hemisphere is tilted away from the Sun. The Sun’s rays are more spread out and have a lower heating effect than in summer.
Don’t forget that there are also longer days when it is summer, so there is more time for the Sun to warm the Northern hemisphere