Friday, December 9, 2011

Occurrence of Day and Night


What Causes Day and Night?
Our solar system consists of nine planets. Earth is one of them. It is the 5th largest planet in the solar system. Like all other planets Earth also revolves round the sun. The earth revolves around the sun in an orbit at a speed of thirty km per second. Earth takes one complete year to make one full revolution round the sun. The diameter of Earth is approximately 12,756 km. Moon is the only natural satellite of Earth. The diameter of the moon is about one fourth that of Earth.
The day and night on Earth occur because of the Earth's rotation around its axis. This axis is actually an imaginary one that runs between the Earth's North Pole and the South Pole. The Earth takes twenty-fours hours to complete one single rotation on its axis. We all know that the sun is the ultimate source of light. When Earth rotates on its axis, the side of the planet facing the sun experiences day. The part of the Earth that does not face the sun experiences night. Remember, the position of the sun never changes. It is always fixed.
There are some who may wonder that if the position of the sun is fixed then why the Sun appears in the east in the morning, overhead at noon and in the west in the evening. It is because throughout the day the Earth moves in its axis from east to west. The duration of the day is taken from the time sun rise until sunset. Also, it is amazing to know that since the Earth is tilted slightly at an angle of 23.5 degrees along its axis, the Southern Hemisphere experiences day and the Northern Hemisphere experiences night. The occurrence of four seasons summer, winter, autumn and spring is also because of the Earth's tilted position on its axis.

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