aajqta
Age: 44 
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Total Posts: 123
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Location:
qta, Pakistan
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The Earth:
The Earth is a sphere but it is not a perfect sphere.
It is slightly flattened at the poles and bulges at the
equator. The circumference of the earth is approximately
25,000 miles (40,000 Kms).
It rotates on its axis once in every 24 hours, spinning
from west to east. Besides spinning on its axis, it also
moves round the Sun, called the revolution.
Its orbit round the Sun is oval or ecliptical. The
time taken to complete one revolution is approximately
365¼ days or one year. For convenience, one year is
taken as 365 days and the shortfall of ¼ day each
year is made good in the Leap Year which consists of
366 days. The Earth’s axis inclined to the plane of its
orbit at an angle of 66½O.
The seasons are due to the change of the Earth’s
position in the course of its revolution about the Sun,
and to the inclination of its axis. The Equator is an
imaginary line drawn round the Earth midway between
the Poles. There are two other lines, namely, Tropic of
Cancer (23½O N) and the Tropic of Capricon (23½O S).
The word tropic means, ‘turning place’. The inclination
of the Earth’s axis together with its revolution round the
Sun is the cause of the varying length of day and night in
different parts of the world. On March 21 (Vernal Equinox)
and September 23 (Autumnal Equinox) the Sun is overhead
at the Equator. On these dates, except at the Poles,
(a) days and nights are equal all over the world; and (b)
the Sun rises exactly due east and set exactly due west at
all places on the Earth’s surface. At the Equator itself
days and nights are equal throughout the year. Between
March 21 and September 23, when the North Pole is tilted
towards the Sun, the days are longer than the nights
throughout the Northern Hemisphere and there is
continuous daylight at the North Pole. Similar conditions
are experienced in the Southern Hemisphere and the
South Pole between September 25 and March 21.
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