Chapter Name: Motion Of The Earth
Subject: Social Science
Lesson: 3
Class: 6
Board: Board Of Secondary Education Manipur (BOSEM/BSEM)
Contents: Chapter, Questions and Answers, Important points to Remember.
The Chapter: Motion of the Earth
We know that like other planets our earth has two motions. It spins on its axis and revolves around the sun. this spinning on the axis is called rotation while movement around the sun is known as revolution.
Rotation
The axis is the imaginary line that joins the North Pole and the South Pole through the centre of the earth. The earth spins on its axis just like a spinning top. This motion is called rotation. The earth takes 24 hours to complete one rotation. We call it one day.
Due to rotation, every part of the earth gets sunlight, turn by turn. The earth is a sphere and therefore, the sun can light up only a half of it. The half, which gets sunlight, has day and the other half, which does not, has night. So, every place on the earth enjoys day and night alternately.
If the earth does not rotate on its axis, the sun would seem stationary in the sky without any movement. The sun does not move at all. It seems to move from east to west because the earth rotates from west to east. It is just like trees and houses that seem to move in the opposite direction when you are on a running bus or train.
Revolution
As the earth rotates on its axis, it also moves around the sun. this motion of the earth around the sun is called revolution. In this movement, the earth follows a fixed path known as orbit. The orbit of the earth is not circular. It is rather oval in shape. Such a shape is called an ellipse.
The earth takes 365 days and 6 hours to complete one revolution. We call it a year. But there are only 365 days in a year. The remaining 6 hours, after 4 years, becomes 24 hours or one additional day. So for every 4 years, we add one day to February.
You will see in the calendar that February has 29 days instead of 28 days once every 4 years. That particular year has 366 days and it is called 366 days and it is called a leap year.
The earth’s axis is inclined at 66 ½ degrees to the plane of the earth’s orbit. From fig., you will notice how much the axis of the earth is tilted.
The earth revolves around the sun in an anti-clockwise direction/Look at fig. carefully. On June 21, because of the tilt of the earth’s axis, the northern hemisphere is inclined towards the sun. this hemisphere receives more heat from the sun and, therefore, enjoys the summer season. On this day, the sun is overhead at the tropic of Cancer and the northern hemisphere has the longest day and the shortest night. This is the summer solstice for the northern hemisphere. Note that there is continuous daylight at the North Pole. The sun never sets in the regions around the north pole.
In Norway, the sun can be seen even at midnight. It is called the midnight sun. But during this time, the southern hemisphere is turned away from the sun. this hemisphere receives slanting rays from the sun and it enjoys the winter season. Thus, on June 21, the southern hemisphere has the longest night and the shortest day. Also, note that there is continuous darkness around the south pole. Here, the sun does not rise at all.
Look at the position of the earth on December 22nd, it is just the opposite of the June 21st position. The southern hemisphere is tilted towards the sun and the northern hemisphere is turned away from the sun. so, there is summer in the southern hemisphere and winter in the northern hemisphere.
On December 22nd, the sun’s rays are vertical over the tropic of Capricorn and the southern hemisphere has the longest day and the shortest night. This day is the winter solstice for the northern hemisphere. Because on this day, the northern hemisphere has the longest night and the shortest day. Note that there is continuous darkness around the north pole and constant daylight around the south pole.
On March 21st and September 23rd, the Earth occupies such a position that the sun’s rays fall vertically at the equator. As a result, the rays of the sun can reach both the north and the south poles. On these two days, day and night are of equal length all over the world i.e., 12 hours of day and 12 hours of night. These two days are called equinoxes.
March is the spring season in the northern hemisphere and autumn in the southern hemisphere. March 21 is known as the vernal equinox in the northern hemisphere. Thus, September 23 is called the autumnal equinox in the northern hemisphere.
Important Points To Remember
👉 The spinning of the earth on its own imaginary line known as the axis is called rotation. The earth spins at a speed of 1666 km/hr and takes 24 hours to complete one rotation
👉 The motion of the earth around the sun is called a revolution. The earth revolves at a speed of 100000 km/hr and takes 365 1/4 days to complete one revolution
👉 The sun does not move but it seems to move from east to west due to the rotation of the earth from west to east.
👉 The movement of the earth around the sun is not circular it is rather oval in shape and the shape is known as an ellipse.
👉 When the month of February has 29 days instead of 28 days once every 4 years and that particular year has 366 days which is known as leap year.
👉 On June 21 the northern hemisphere receives more heat as the sun is overhead at the
Tropic of Cancer and it enjoys the summer season that has the longest day and the shortest night. This is the summer solstice for the northern hemisphere.
👉 On June 21 the northern hemisphere receives more heat as the sun is overhead at the tropic of Cancer and it enjoys the summer season that has the longest day and the shortest night. This is the summer solstice for the northern hemisphere. But on the same day (i.e., 21st June), the southern hemisphere has the longest night and the shortest day and it has the winter season.
👉 Likewise, on December 22, the sun’s rays are vertical over the tropic of Capricorn and the southern hemisphere has the longest day and shortest night and enjoys the summer season but the northern hemisphere has the winter season and it has the longest night and the shortest day. This day is the winter solstice for the northern hemisphere. There is continuous darkness around the north pole and constant daylight around the south pole.
👉 At the north and the south poles, the days and nights are six months long.
👉 March is the spring season in the northern hemisphere and autumn in the southern hemisphere.
👉 September is the autumn season in the northern hemisphere and spring in the southern hemisphere.
👉 March 21st is known as the vernal equinox and September 23 is called the autumnal equinox in the northern hemisphere.
BOSEM Solutions for the Chapter Motion Of The Earth
Question And Answer
Q1. How long does the earth take to complete one rotation?
Ans: The earth takes 24 hours to complete one rotation
Q2. Why does the sun seem to move from east to west?
Ans: it is due to the rotation of the earth from west to east
Q3. What is an ellipse?
Ans: the movement of the earth around the sun is not circular but rather oval in shape. Such a shape is called an ellipse.
Q4. What are the two motions of the earth?
Ans: The two motions of the earth are rotation and revolution. Rotation means spinning of the earth on its own axis whereas revolution means the movement of the earth around the sun.
Q5. What is a leap year?
Ans: when the month of February has 29 days instead of 28 days once in every 4 years and that particular year has 366 days which is known as leap year.
Q6. What is midnight sun?
Ans: In Norway, the sun never sets and we can see the sun even at midnight as there is continuous daylight in the north pole and it is known as the midnight sun.
Q7. What are equinoxes?
Ans: On March 21 and September 23, the day and night are equal all over the world. These two days are called equinoxes.
