Motions of the earth notes

Q4) What is revolution? What are the effects of the Earth’s revolution?

Ans. Revolution is the movement of the earth around the sun on a fixed orbit. This orbit is elliptical in shape.

The revolution causes

i)      occurrence and change in the seasons,

ii)                Leap year also happen due to revolution,

iii)             Variation in the length of days and nights

iv)             Distribution of heat over the Earth

Q5) Write short notes :

a)    Leap Year: The Earth takes 365 ¼ days to complete one revolution around the sun. For our convenience , we consider a year equal to 365 days. The remaining ¼ day is compiled to make one complete day of 24 hours. Ie( 24 hours / 4 = 6 hours). This extra day is added to the month of February every fourth year. This year is known as a leap year. In a leap year February has 29 days instead of 28 days.

b)   Seasons: The seasons occur due to the revolution of the earth. There are mainly 4 seasons- spring, summer, autumn and winter. The seasons occur due to four different  position of the earth. These positions of the earth are named based on the season experienced in the Northern Hemisphere at that particular time of the year.

c)    Spring Equinox: The sunrise falls vertically on the equator, causing equal days and nights all over the Earth The northern hemisphere has blooming spring while  the southern hemisphere has chilly autumn. This occurs on 21 st March.

d)   Summer Solstice: The day is referred to as being the longest day and the shortest night in the Northern hemisphere. Due to inclination of the Northern Hemisphere towards the sun, the vertical rays directly fall on the Tropic of Cancer and slanting rays fall on the Tropic of Capricorn. Thus , it is summer in Northern hemisphere and winter in Southern hemisphere. This position of the Earth is known as ‘Summer Solstice’. This happens on 21^st  June.

e)   Autumnal Equinox: On the 23^rd  September, the sun again shines vertically over the equator. The duration of days and nights in both the hemispheres are equal. The seasons are just reversed, the Northern hemisphere has autumn and the southern hemisphere has spring. This is termed as ‘Autumnal Equinox’.

f)     Winter Solstice:  In this position of the earth, vertical sunrise fall on Tropic of Capricorn and slanting rays falls on Tropic of Cancer. The Northern hemisphere has winter with shorter days while the southern hemisphere enjoys summer with longer days. This is known as ‘Winter Solstice’. 22^nd December is the longest day in the Southern hemisphere.

6) How does the revolution of the earth cause variations in the length of days and nights?

Ans: The revolution of the Earth on its inclined axis around the sun causes longer days in summer than in winter. The variation between the lengths of the day and the night is minimum at the equator. It increases gradually towards the poles. Thus the North Pole and the South Pole experience 6 months daylight and 6 months night.

6) Why is it extremely hot at the equator?

Ans: It is extremely hot at the equator as that part of the earth receives vertical rays of the sun. The poles receive slanting rays thus it is freezing cold at the North Pole and South Pole.