Meaning of Rotation and Revolution of the Earth

Rotation of the Earth:

The Rotation of the Earth is the movement of the Earth, on its axis in an anti-clockwise direction, that is, from West to East. It takes the Earth twenty-four (24) hours to complete a rotation, so it takes 24 hours for Earth to complete a 360° circular movement.

The Earth rotates on its axis from west to east. Because of this, the Moon, the Sun and all other celestial objects appear to move from east to west across the sky.

The rotation of the Earth leads to the following effects;

1. Day and night.
2. Deflection of wind and ocean currents.
3. A difference of one hour between places that are 15° apart, as you go from East to West.
4. Daily rising and falling of tides.
5. Apparent Sunrise and Sunset.

As the Earth rotates from West to East, the portion facing the sun receives sunlight and, therefore, experiences daylight at that time. The other portion of the Earth that is not facing the sun will experience darkness. There is an imaginary line that separates day from night on the Earth, this is called the Circle of Illumination. 

However, due to the rotation of the Earth on its axis to complete 360° all parts of the Earth will experience sunlight at some point. Any part of the earth that emerges from darkness to receive the sun’s rays is experiencing the sun rising. However, due to the Earth’s rotation, it will gradually be obscured from the sun’s rays and therefore experience the sun setting.

The sun does not move or rotate, rather it is the Earth that moves or rotates.

Revolution of the Earth:

The Revolution of the Earth is the movement of the Earth around the Sun in its orbit. It takes the Earth 365 ¼ days to complete a revolution around the sun, which is equivalent to one year. It is difficult to indicate a ¼ of a day which is equal to 6 hours and approximate it within the number of days it takes for the Earth to complete a revolution. An extra day (which is 24 hours) is added to February, every fourth year, which means every fourth year February has 29 days instead of 28. This is done to accommodate the ¼ of a day (or 6 hours) in every complete revolution of the Earth.

A year with 366 days is known as a leap year, the other three (3) years have 365 days.

The Revolution of the Earth is responsible for the different seasons experienced on the Earth and the varying lengths of day and night at different times during the year.

The Earth’s axis which is an imaginary line makes an angle of 66½° with the Earth’s orbital plane and it always points in the same direction. The angle of the Earth’s axis with the vertical or ecliptic plane is 23.5 ½°.

How the Earth Revolves Around the Sun:

As mentioned, the Earth completes a revolution around the sun once every 365¼ days (approximated to 365 days).

The Earth revolves around the Sun at a speed of 107,000 km/hr (67,000 miles per hour) and rotates about its axis at a speed of 1600 km/hr (1,000 miles per hour). When these speeds are considered, it is surprising that we do not feel the movement of the Earth, due to a powerful force generated by the Earth’s mass known as the force of gravityThe force of gravity, or gravitational force, pulls objects with mass toward each other. More.

The force of gravity is the Earth’s force of attraction that pulls all human beings, animals and all other objects towards its centre.

Note: Refer to the above diagram, showing the various positions of the Earth (in relation to the Sun), at different times of the year as we discuss the varying lengths of day and night in different HemispheresA hemisphere is half the Earth's surface. The four hemispheres are the Northern and Southern hemispheres, divided by the equator (0° latitude), and the Eastern and Western hemispheres, divided by the... More.

We know the number of days it takes the Earth to revolve around the Sun determines the length of the year. We also need to know that the revolution of the Earth is responsible for the varying lengths of day and night at different points of the year.

How the Revolution of the Earth Determines the Length of Day and Night at Different Times of the Year:

The length of day and night varies depending on the position of the Earth as it revolves around the Sun.

In areas around the EquatorThe Equator is Zero degrees (0°) latitude. The Sun is directly overhead the equator at noon on the two equinoxes (March and Sept. 20 or 21). The equator divides the globe... More, there isn’t much variation in the lengths of day and night. However, there are differences in the lengths of days and nights during different periods of the year especially in the temperate region – that is, in areas not close to the Equator. On September 23rd and March 21st, the sun is overhead at noon-day at the equator. On both these days, all the different parts of the world experience equal daylight and darkness, this means, 12 hours of daylight and 12 hours of darkness. September 23rd is called the Autumn Equinox and March 21st is the Spring Equinox.

On the 21st of June, at noon the sun is overhead at the latitude of 23.5° North, over the Tropic of CancerThis line of latitude is located 23°30' north of the equator. The Sun is directly overhead the Tropic of Cancer on the summer solstice in the Northern Hemisphere (June 20 or... More. June 21st is also called the Summer Solstice, all parts of the Earth in the Northern Hemisphere experience longer hours of sunlight and smaller hours of darkness. In areas further away from the Equator, from the Arctic Circle at 66.5° North to the North Pole, they experience 24 hours of daylight on June 21st. The opposite effect occurs in the Southern Hemisphere during the Summer Solstice on June 21st. In areas in the Southern Hemisphere, they experience longer hours of darkness and shorter hours of sunshine.

On December 22nd, at noon the sun is overhead at the latitude of 23.5° South, over the Tropic of CapricornThis is a line of latitude located at 23°30' south. The Sun is directly overhead the Tropic of Capricorn on the summer solstice in the Southern Hemisphere (Dec. 20 or 21).... More. December 22nd is known as the Winter Solstice, all parts of the Earth in the Southern Hemisphere experience longer hours of sunlight and smaller hours of darkness. In areas from the Antarctic Circle to the South Pole, they experience 24 hours of sunlight on the 22nd of December. During the Winter Solstice, the Northern Hemisphere tilts the farthest away from the Sun. As a result, the Northern Hemisphere experiences longer hours of darkness and smaller hours of sunshine.

Note: The sun is never overhead outside the Tropic of Cancer (23.5° North) and the Tropic of Capricorn (23.5° South). This means the Sun is never overhead outside the latitudes of 23.5° North and South of the Equator. The apparent movement of the Sun is continuous between the Tropic of Cancer (23.5° North) and the Tropic of Capricorn (23.5° South).