The earth while rotating on it axis also revolves around the sun. This movement of the earth round the sun called earth’s Revolution. The path of the movement is called orbit. July 4th the earth is far from the sun and is said to be in Aphelion position. Aph means away and hellion means Sun. At this point the distance between the sun and the earth is 152 million km. Jan 3rd the earth is nearest to the sun and is said to be in Perihelion position. Peri means near, hellion means sun. At this point the distance between the.sun and the earth is 147 million km. Effects of Revolution:
The major effects of revolution are
- In equality of day and night.
- Occurrence of seasons.
- Distribution of important lines of latitude.
- Different climatic zones
In equality of day and night: The duration of day and night are not uniform, along all . degrees of latitudes through out the year. The variation in the length of day and night is caused by the inclination of the earth’s axis and revolution of the earth.
The angle of inclination of the earth is 23 1/2 away from the perpendicular to the plane of the ecliptic and its direction is constant through out orbit. So the vertical rays of the sun moves form 23 1/2 N to 23 1/2S latitudes. From September 23 to march 21 the North Pole of the earth is tilted away from the sun and experiences darkness. At the same period the South Pole experiences day. At the equator the duration of day and night are almost equal though out the year.
Occurrence of Seasons: It is the most important effect caused by the revolution of the earth. The variations of temperature when the earth is at different location on its orbit are called the seasons. The difference of temperature in a duration of one year is caused as a result of Inclination of the earth’s axis and its parallelism.
There are four seasons in a year. They are:
1. Summer
2. Autumn
3. Winter
4. Spring.
As per the international Calendar, the four seasons have a period of three months. From the point of view of the earth’s indication, there are four positions of solstices and equinoxes. So, there are four seasons according to the positions of the earth in one complete revolution around the sun. Those four seasons are:
Summer Solstice: On June 21st the northern hemisphere is tiled towards the sun while the southern hemisphere is tilted away from the sun. The rays of the sun fall vertically on the Tropic Cancer and he areas within the Artistic circle remain in sun light for all 24 hours. The northern hemisphere has longer days and shorter night. At this time the northern hemisphere has longer days and shorter night. At this time the northern hemisphere enjoys summer season and this potion is called “ summer solstice”. Solstice means sun stops.
Autumnal Equinox: On the 23rd September the northern hemisphere and the southern hemisphere are equally inclined or tilted towards the sun. The sun rays are vertical at the equator. As a result, the days and night are equal all over the world. At this time, in the northern hemisphere the season is neither hot nor cold. It is a situation between summer and winter seasons. It is called autumn season. At this time in the southern hemisphere, there is spring season. This position of the earth on 23rd September is known as autumnal equinox.
Winter Solstice: On 22nd December the southern hemisphere is inclined or tilted towards the sun, and northern hemisphere is inclined or tilted away from the sun. The sun is vertical at the Tropic of Capricorn, i.e. at 23 os. At this time there is winter season in the northern hemisphere, and summer season in the southern hemisphere. This position is known as winter solstice.
Spring or Vernal Equinox: On 21st March the northern and southern hemisphere are equally inclined towards the sun. The conditions are similar to those of autumnal equinox. From 21st March to 21st June, the earth is moving on its northern limits. During this period, there is spring season in the northern hemisphere and autumn season in the southern hemisphere.
Distribution of important lines of latitude. Based on the revolution important latitudes such as equator, Tropic of cancer, Tropic of Capricorn, arctic and Antarctic circles are recognized.
Different climatic zones: The different climatic zone is the result of the revolution of the earth. Climatic zones depend on the important lines of latitude.
Between the equator and the tropic of cancer, we have the North Torrid Zone. Between the Equator and the Tropic of Capricorn, we have the South Torrid Zone Between the Tropic of Cancer and the Arctic Circle, we have the North Temperate Zone. Between the topic of Capricorn and the Antarctic Circle, we have the south temperature Zone, between the Arctic Circle and the North Pole we have the North rigid zone, and between the Antarctic Circle and the South Pole, we have the South Frigid Zone.
