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Current affairs forms an important component of several competitive exams such as the UPSC Civil Services Examination, SSC CGL, Bank PO and PSU entrance tests, etc. Therefore, understanding terms/concepts/events that are in the news is critical for aspirants. We at PaGaLGuY bring you this series of articles explaining some of these important concepts/events in detail.

In this article we are discussing our Earth.

Earth is a unique planet in the solar system because of presence of life. It is because the Earth has the presence of water and biosphere. 

Shape of the Earth:

a) The shape of the Earth is close to a geoid or oblate spheroid.  It is so because the Earth is bulging at the equator and flat on the poles.

b) The Earth’s equatorial circumference is 24,897 miles. However, the circumference at the polar region is 83 miles less than that of the equilateral circumference due to the flat structure at the polar region.

c) The bulge at the equator is produced by the centrifugal force acting on the rotating Earth. 

d) The gravitation force at the equator is minimum whereas it is maximum at the poles.

e) Earth’s equator is a virtual line dividing the Earth’s sphere into two equal, horizontal parts. The line that goes through the core of Earth and joins the North and South Pole is called the Geographical Axis.

Earth’s movements :

a) The Earth moves in two distinct ways. It rotates on its own axis from west to east (anti-clockwise) every 24 hours causing day and night. It also revolves around the Sun in an elliptical orbit once in every 365 ¼ days causing change in the year and the seasons.

b) Earth spins around the Sun at a speed of 18.5 miles per second. 

c) The axis of the Earth is inclined towards the Sun at an angle of 66 ½ degrees thereby resulting in change in seasons and variations in lengths of days and nights. In winter season, if we go northward, the hours steadily increase.  At the North Pole, half the year is dark. During mid-winter, on December 22, it is dark the whole day.

d) During summer, the conditions get reversed. Thus, at the North Pole the Sun never sets on June 21 and there is six months of continuous daylight.

e) In the southern hemisphere the same conditions occur, but exactly reversed. 

The midday Sun:

a) Due to Earth’s inclined axis, the Sun is vertically overhead at the equator on two days every year. These are usually March 21 or September 21.  These two days are termed as equinoxes i.e. equal night and day. 

b) After the March equinox, the Sun appears to move north and is vertically overhead at the Tropic of Cancer on June 21. This is known as June or summer solstice. On this day, the northern hemisphere experiences longest day and shortest night.

c) After the September equinox, the Sun appears to move south and is vertically overhead at Tropic of Capricorn on December 22. This is known as winter solstice. On this day, the northern hemisphere experience shortest day and longest night.

d) During summer, the Sun is higher in the sky than in winter. Due to this, its rays fall on Earth vertically, the heat concentrated on a small area. Hence, summers are hot.

e) During winter, the oblique rays of Sun come through less directly and much of the heat is absorbed by the atmosphere. Also, they spread over bigger area thereby making winters cold.

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