Motions Of The Earth And Their Effects

The earth is not stationary. It rotates on its revolves round the sun and moves, along with the system around the galaxy, even as the galaxy in its en! moves through the universe.

Here, however, we are concerned mainly with two motions-rotation and revolution.
ROTATION It is the movement of the earth on its axis from the west to east, so that the stars, the sun and the moon appear to rise in the east and set in the west. Each rotation takes 23 hours 56 minutes and 4.09 seconds. The velocity of rotation of an object on the earth's surface at the equator is about 1700 km per hour and it decreases towards the poles. Earth's rotation results in (i) causation of day and night; (il) a difference of 1 hour between two meridians which are 15" apart; (iii) deflection of ocean currents and winds-see figure below; (iv) rise and fall of tides every day.
REVOLUTION It is earth's motion in its elliptical orbit around the sun. Earth's average orbital velocity is 29.79 km/sec. One revolution is completed in 36514 days, result­ing in one extra day every fourth year. This year, consisting of 366 days, for convenience is called the 'leap year' having 29 days in the month of February. Revolution of the earth results in: (i) the change of seasons; (ii) variation in the lengths of day and night at different times of the year; (iii)
differences in altitudes of the sun at noon, at different times of the year.
-It may be noted that as the earth's orbit is elliptical, the distance between the earth and sun keeps changing. The point on the orbit nearest to the sun is the perihelion which is 147 million km and occurs around January 3; the
point of maximum distance is aphelion which is 152 million km and occurs around July 4.
Inclined Axis Inclination of the earth's axis is an important feature of the earth-sun relationship. In its elliptical movement around the sun, earth's axis makes a constant angle of 661,20 with the plane of the ecliptic, and is tilted 231,20 from a line perpendicular to this plane. The two facts, Le., a fixed angle of the earth's axis to the plane of the ecliptic and the axis always pointing in the same direction, when combined with the earth's movements, result in varying lengths of day and night, seasonality and changes in the altitude of sun at different times of the year.