MOVEMENTS OF THE EARTH
The changing seasons is caused by the movements of the Earth. There are two important movements that affect the Earth.
- The first is the rotation of the Earth around an invisible axis. It takes the Earth about 24 hours to finish one complete rotation.
- The second important movement that affects the Earth is its revolution around the Sun. One revolution takes 365 ¼ days, or one year.
ROTATION OF THE EARTH
The Earth rotates counterclockwise; this is why the Sun “rises” in the East and “sets” in the West. The Earth also rotates, or spins, on its axis. It takes one day to spin around itself one complete time. The Earth’s axis is not straight up and down, but tilted at an angle of 23.5 degrees. The rotation is what causes the change from day to night. This tilt is responsible for having seasons. If the Earth were not tilted, we would have the same season all year long. The spinning of the Earth around its own axis causes day and night. It takes 24 hours to complete one rotation. However, sunlight shines only on the half of the Earth facing the Sun. That half has day the other half is dark and has a night.
REVOLUTION OF THE EARTH
The movement of the Earth around the Sun in a fixed orbit is called as revolving. One full orbit around the sun is one revolution. The Earth takes 365 days or 1 year to complete one revolution. The Earth revolves around the Sun because of gravity. The Earth really rotates 365 ¼ times during each revolution. The calendar always has 365 days, after every 4 years, the earth has made one extra rotation. However, one extra day is added to the month of February once in every four years forming a leap year with 366 days.
The Earth takes about one year to revolve around the Sun, and also it rotates on its axis. The axis on which the Earth rotates is slightly tilted, and this causes the cycle of seasons. While the Earth is revolving, if the Northern Hemisphere gets the direct sunlight, it has summer and on the other side, the Southern Hemisphere, will have winter. When the Southern Hemisphere faces direct sunlight it will have summer and it will be winter in the Northern Hemisphere.
At two points throughout the year, the tilt of the Earth’s axis reaches its maximum angle compared to the Sun, and begins to move back the other direction. This usually happens around June 21st and December 21st. These days are known as solstices. On these solstices, the length of day or night reaches its maximum. Winter solstice is the shortest day of the year. Summer solstice is the longer day of the year.
As the Earth moves around its orbit, it reaches two points during the year where the tilt of its axis causes it to be straight relative to the Sun. These days are known as equinoxes. During these equinoxes the rays of the Sun shine directly on the equator. This happens on approximately March 20th and September 22nd. In these days, night and day have the same length,