b) Revolution:
At the same time as the Earth rotates on its own axis, it also moves around the Sun in an elliptical orbit. It takes the Earth 365 days and six hours to complete one revolution.
As our calendar only has 365 days, there is a leap year every four years. That's the reason why every four years February has got 29 days.
The axis of the Earth is tilted slightly. This causes part of the Earth to lean towards the Sun while part of it is hidden, causing different parts of the Earths surface to receive a different amount of sunlight and heat. This movement causes the seasons, which are reversed in both hemispheres.
In summer, the Sun's rays reach the Earth vertically (solstices). At the same time, it is winter in the other hemisphere.
In Spring and Autumn the Sun's rays reach both hemispheres at a similar angle (equinoxes).
At the same time as the Earth rotates on its own axis, it also moves around the Sun in an elliptical orbit. It takes the Earth 365 days and six hours to complete one revolution. As our calendar only has 365 days, there is a leap year every four years. That's the reason why every four years February has got 29 days.
The axis of the Earth is tilted slightly. This causes part of the Earth to lean towards the Sun while part of it is hidden, causing different parts of the Earths surface to receive a different amount of sunlight and heat. This movement causes the seasons, which are reversed in both hemispheres.
In summer, the Sun's rays reach the Earth vertically (solstices). At the same time, it is winter in the other hemisphere.
In Spring and Autumn the Sun's rays reach both hemispheres at a similar angle (equinoxes).
A
L
C