Rotation: This refers to the movement of the Earth on its own axis. Imagine a straight line passing through the Earth from the North Pole to the South Pole; this is its axis. The Earth spins or rotates around this axis. Due to this rotation, we experience day and night. The Earth completes one rotation approximately every 24 hours, and this period is what we call a day.

Revolution: This is the movement of the Earth around the Sun in a specific pathway or orbit. The Earth takes about 365¼ days to complete one full revolution around the Sun. This period is what we recognise as a year.

The ancient Indian astronomer Aryabhata had stated that ‘the earth is round and rotates on its own axis’.

The Earth’s axis is an imaginary line that tilts at an angle of 66½° with its ‘orbital plane’, the plane in which Earth revolves around the Sun.

Circle Of Illumination And Day–Night Cycle

Due to Earth’s spherical shape, only one half of it receives sunlight at any given moment. The dividing line between the daylight side and the night time side is called the ‘circle of illumination’. Because of Earth’s tilt and its rotation, this circle doesn’t align perfectly with the axis.