KERALA PSC / PHYSICAL GEOGRAPHY / MOTIONS OF THE EARTH AND THEIR CONSEQUENCES / NOTES

 

KERALA PSC / PHYSICAL GEOGRAPHY / MOTIONS OF THE EARTH AND THEIR CONSEQUENCES / NOTES

KERALA PSC / PHYSICAL GEOGRAPHY / MOTIONS OF THE EARTH AND THEIR CONSEQUENCES / NOTES

·       The movement of earth can be mainly divided into two as, rotation and revolution

·       Rotation is the spinning of earth on its on axis

·       Earth spins on its axis at an angel of 66½º to the plane of earth from west to east

·       Earth’s rotation takes 23 hours, 56 minutes and 4.091 seconds to complete one rotation

·       Rotation results in the formation of day and night, changes in the direction of wind and ocean currents. The daily occurrence of tides twice is also resulted by the rotation of earth.

·       Day and night are not to equal duration throughout the year because of the tilt of earth’s axis

·       Earth rotates 1º in 4 minutes. Therefore earth rotates 15º in one hour. It takes 24 hours (one day) to complete one rotation (360º)

·       Day and night are equal at the equator throughout the year, because the circle of illumination always divides the equator into two equal parts

·       The duration of day and night at the poles is six months each

·       Rotation also causes Coriolis forces (named after the French mathematician Gaspard de Coriolis who first explained them mathematically) which are related to the decreasing rotational velocity with increasing latitude and tend to deflect anything which is moving over the earth’s surface.

·       Coriolis force is zero at the equator and increases progressively towards either poles

·       The most celebrated test of Earth’s rotation is the Foucault pendulum first built by physicist Leon Foucault in 1851

·       Revolution is the movement of earth in its orbit around the sun, along an almost circular path (elliptical) called its orbit. The earth revolves approximately one degree in one day. The speed of revolution of earth is 29 km/second.

·       The earth takes 365.25 days to complete one revolution

·       The earth’s revolution causes a change in seasons. Seasons are classified into four called the Spring, summer, Autumn and Winter. The earth’s axis is inclined at an angle of 66½º to the plane of its orbit.

·       Equinoxes are dates when the night and days are equal. During these days the sun shines vertically on the equator. This occurs twice a year. March 21 is called the vernal equinox or Spring equinox and September 23 is called autumnal equinox

·       Solstice is the time of the year when the difference between the length of days and the length of nights is the largest. During these days, the sun shines vertically over the tropic.

·       On or around June 21, the North pole tilts towards the sun and the sun shines directly over the tropic of cancer. This is called Summer Solstice. On or around December 22, the earth is at the end of its orbit. The South pole tilts towards the sun and the North pole away from it, which is called as Winter Solstice.

·       Tropics are the regions circling the earth between the Tropic of Cancer (23º27’N) and the Tropic of Capricorn (23 º27’S). These imaginary lines of latitude, mark the farthest points reached by the sun’s vertical rays. The 23½ º North parallel is termed as Tropic of Cancer and the 23½ º South parallel is termed as Tropic of Capricorn.

·       Sun rays fall vertically at the Tropic of Cancer on June 21 and they fall vertically at the Tropic of Capricorn on December 22

·       Aphelion is the point in the Earth’s or other planets orbit which is farthest from the sun. Earth is at its aphelion on July 4 every year at a distance of 152 million kilometers.

·       Perihelion is a point in the orbit of a planet or any other celestial body at which it passes closest to the sun. Earth will be at its perihelion on January 3 every year at a distance of 147 million kilometers.

·       Perigee is the point in the orbit of the moon at which it is closest to the earth. A pogee is the point in the orbit of the moon at which it is farthest from the earth.

 

 

KERALA PSC / PHYSICAL GEOGRAPHY / MOTIONS OF THE EARTH AND THEIR CONSEQUENCES / NOTES