The Earth also called Blue Planet. It is the densest of all planets.
Earth Circumference : 40,232 Kilometers.
Earth Area : 510 million Square Kilometers Average distance from sun: 149 million-Kilometers.
Earth Perihelion : Nearest position of earth to sun. The earth reaches its perihelion on January 3 every year at a distance of about 147 million-Kilometers.
Aphelion : Farthest position of earth from sun. The earth reaches its aphelion on July 4, when the earth is at a distance of 152 million Kilometers.
The shape of the earth is oblate spheroid or oblate ellipsoid (i.e. almost spherical, flattened a little at the poles with a slight bulge at the centre).
- Rotation or daily movement.
- Revolution or annual movement.
- Spins on its imaginary axis from west to east in 23 hrs, 56 min and 40.91 sec.
- Rotational velocity at equator is 1667 Kilometers/h and it decreases towards the poles, where it is zero.
- Earth’s rotation results in
i . Causation of days and nights;
ii . A difference of one hour between two meridians which are 15° apart;
iii. Change in the direction of wind and ocean currents;
- Rise and fall of tides everyday.
The longest day in North Hemisphere is June 21, while shortest day is on 22 Dec (Vice-versa in S. Hemisphere).
- Days and nights are almost equal at the equator.
- It is earth’s motion in elliptical orbit around the sun. Earth’s average orbital velocity is 29.79 Kilometers/s.
- Takes 365 days, 5 hrs, 48 min and 45.51 sec. It results in one extra day every fourth year.
- Revolution of the earth results in
i . Change of seasons
ii . Variation in the lengths of days and nights at different times of the year
iii . Shifting of wind belts
iv . Determination of latitudes.
- Inclined Axis: The axis is an imaginary line running from north to south and passing through the centre of the earth. It always remains inclined at an angle of 66½° to the plane of the earth’s orbit, and is tilted 23½° from a line perpendicular to this plane. The two facts, i.e., a fixed angle of the earth’s axis to the plane of the orbit and the axis always pointing in the same direction, when combined with the earth’s movements, results in varying lengths of days and nights, seasonality and changes in the altitude of sun at different times of the year.
- Earth Seasons are periods into which the year can be divided as a result of the climatic conditions, largely due to the changes in the duration and intensity of solar radiation.
The 4 Earth Seasons are:
- Spring: On March 21, the sun is directly overhead the equator. This is the season of spring in the northern hemisphere.
- Summer: On June 21, the sun is directly overhead the Tropic of Cancer. Thus, the northern hemisphere experiences summer.
- Autumn: On September 23, the sun returns to the equator, and the northern hemisphere experiences autumn.
- Winter: On December 22, the sun is at the Tropic of Capricorn, and the northern hemisphere experiences winter.
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