CHAPTER 3 MOTIONS OF THE EARTH The Earth is always travelling in Space. That makes each person on Earth, a Space Traveller. No one feels the movement of the Earth because humans are too tiny when compared to the size of the Earth. People can only become aware about the movement of ROTATION by the Earth, by observing the rising Sun, the Sun at Noon when it is high in the sky, and the setting Sun in the evening. This is followed by the rising of the Moon at or after Sunset, and its changing position in the night sky, and its setting in the morning. Through these two daily rising and setting of the Sun and the Moon, people on Earth get to know that the Earth has been moving by Rotating on its axis. When the days in summer become longer because the Sun rises earlier and sets later, we know that the Earth is moving around the Sun in its own Orbit. In summer, the Sun is on the North side of the Earth, therefore, days are longer. In Winter the Sun is in the South side of the Earth, therefore the days are shorter while nights become longer. When the Earth is in the East or the West of the Sun, the days and nights are equal in all places on Earth. This is because then the Sun is directly in line of the Equator or middle part of the Earth. This position is given in Fig 3.3 on page 19. In Chapter 3 these two movements or motions of the Earth are discussed in detail. 1. ROTATION: is the daily movement of the Earth to complete one circle around its own AXIS. Day and Night are caused because of ROTATION. It takes 24 hours for the Earth to complete one Rotation. 2. REVOLUTION: is the annual movement of the Earth, to complete one circle around the Sun. This takes the Earth 365¼ days or one whole year to complete one REVOLUTION. This causes changes in Seasons of Summer, Rainy season, Autumn, Winter, Spring. 10x10learning.com Page 1
The complete circle around the Sun is called the Orbit of the Earth. Orbit is an invisible road on which the Earth travels around the Sun. All the planets in the Solar System, have their own invisible path or Orbit on which they move around the Sun. EXERCISES at the end of the Chapter 1. Answer the following questions: a) What is the angle of inclination of the earth s axis with its orbital plane? Ans. The angle of inclination of the earth s axis with its orbital plane is 66 ½ 0. b) Define rotation and revolution. Ans. Rotation is the daily motion of the earth, on its own axis, and is completed in 24 hours. Rotation causes day and night. Revolution is the motion of the earth in its own orbit around the Sun. It is completed once in 365¼ days or one year. It causes changes in seasons, and makes the days longer or shorter. c) What is a leap year? Ans. One revolution of the earth is completed in 365 ¼ days. The ¼ day is equal of 6 hours. This fraction of 6 hours gets carried forward for three years. In the fourth year it totals 6+6+6+6 = 24 hours= 1 day. Therefore, one additional day is added to the fourth year in the month of February. Thus, a leap year comes every fourth year and has 366 days. February has 29 days in place of 28. d) Differentiate between the Summer and Winter Solstice. Ans. It is better to answer questions on differentiate, compare and contrast in tabular format. However, a student is free to write it in two paragraphs, by discussing the two solstice in two paragraphs. Tabular format is used here. Summer solstice Winter solstice 10x10learning.com Page 2
1. Occurs on 21 st June every year 2. The Sun is in a straight line and over head Tropic of Cancer at 23½ 0 North. 3 In the northern hemisphere days are longer and nights are shorter. In the southern hemisphere days are shorter and nights are longer. 4. It is summer season in the northern hemisphere and winter in the southern hemisphere 5. The Sun does not set at the North Pole for six months, And it can be seen at the horizon from March to September. Occurs on 22 nd December every year The Sun is in a straight line and over head Tropic of Capricorn at 23½ 0 South. In the southern hemisphere days are longer and nights are shorter. In the northern hemisphere days are shorter and nights are longer. It is summer season in the southern hemisphere and winter in the northern hemisphere. The Sun does not set at the South Pole for six months, and it can be seen at the horizon from September to March. e) What is an equinox? ( Also see Figure 1 on next page) Ans. Equinox occurs twice in one year, on 21 st March, and 23 rd September, when the Sun is directly overhead the Equator at 0 0 latitude. On these two days, the duration of day and night is equal in all places on the earth because the Sun is shining directly on the middle portion of the Earth. f) Why does the Southern Hemisphere experience winter and Summer Solstice in different times than that of the Northern hemisphere? Answer. The North and South hemispheres have solstice at different times because the position of the Sun is different when these two solstices occur. The Sun is directly overhead the Tropic of Cancer at 23½ 0 North on 21 st June. It is directly overhead the Tropic of Capricorn at 23½ 0 South, on 22 nd December. g) Why do the poles experience about six months day and six months night? 10x10learning.com Page 3
Ans. The axis of the Earth at the North Pole is inclined at an angle of 23½ 0 towards the east. This make the earth tilt towards the Sun, making the sunlight to reach the north pole continuously for six months. This happens from March to September when the northern hemisphere is in direct line with the Sun. During this period there is continuous night at the south pole, because it is in the shadow region from the Sun. From September to March, the Sun moves towards the south of the earth. Therefore, the south pole gets exposed to the sunlight continuously for six months. Additional: The North and South Poles are both at the top end and bottom end of the earth. They are located at 66 ½ 0 North and 66½ 0 South of equator. The Sun never goes beyond 23 ½ 0 North or South of Equator. This means that the Sun is never overhead the two poles, like it is overhead at noon in other places. Throughout the six months of day at the Poles, the Sun is visible only at the horizon, as if it is rising or setting. It is at a fixed spot and does not move in the sky as it does in other places. Sun in line with Tropic of Cancer at 23½ 0 North on 21 st June 21 st March and 23 rd September Sun in straight line with Equator, 0 0 latitude. This occurs twice during the Earth s Revolution, in its orbit. Sun in line with Tropic of Capricorn 23½ 0 South on 22 nd December Straight line rays of the Sun, also called the direct rays, fall only on the area between the two Tropics. The three arrows indicated here show the daily Rotation of the earth around its own axis. The Earth rotates from west to east. Axis is shown as the arrow going through and through indicating the North Celestial Pole. 10x10learning.com Page 4
2. Tick the correct answers. ( Correct answer is in colour here) (a) The movement of the earth around the sun is known as (i) Rotation (ii) Revolution (iii) Inclination (b) Direct rays of the sun fall on the equator on (i) 21 March (ii) 21 June (iii) 22 December (c) Christmas is celebrated in summer in (i) Japan (ii) India (iii) Australia (d) Cycle of the seasons is caused due to (i) Rotation (ii) Revolution (iii) Gravitation 3. Fill in the blanks. (a) A leap year has 366 number of days. (b) The daily motion of the earth is Rotation. (c) The earth travels around the sun in an elliptical orbit. (d) The sun s rays fall vertically on the Tropic of Capricorn on 21st June. (Note: This is because the direct rays are falling on Tropic of Cancer on 21 st June. Therefore, in the southern hemisphere the rays have to be vertical. These are called higher order questions or Trick questions to check if the students has really understood the fundamental issues. Always read the question twice) (e) Days are shorter during Winter season. 10x10learning.com Page 5
CHAPTER 4 MAPS A map is a sketch or a drawing of a portion of the Earth. Maps are of different kinds: Physical maps, Political maps, Thematic maps. Examples of a thematic map of ocean currents and a physical map of India are given below. Figure1. Example of a thematic map of the spread out or flattened globe, indicating all the major ocean currents of the world. Figure 2 on the next page, is an example of the Physical Map of India. Note how the rivers and the oceans / seas are all in blue colour, grassy plains are shown in green, deserts are yellow, and mountains are in brown. International boundaries with Nepal and other neighbouring countries is in light purple. Please also note the grid made from the latitudes and longitudes between which India is located. See the Indian Standard Time latitude at 82½ 0 East. Note the indication in the lower south eastern corner that Map not to scale. Link it to the three components of the map in the chapter, namely, distance, direction and symbol. Map not to scale means this may does not 10x10learning.com Page 6
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1. Answer the following questions briefly. (a) What are the three components of a map? Answer. The three components of a map are direction, distance and symbol. (b) What are the four cardinal directions? Answer. The four cardinal directions are North, South, East and West (c) What do you mean by the term the scale of the map? Answer. The scale of the map means the ratio between the actual distance on the ground, and the distance shown on the map. If a distance from place A to place B is 10 kilometres, it is shown on the map as 2 cm. This means the scale is 1 cm for every 5 kilometres. On this basis, a map could be a small scale map, that gives only broad information or a large scale map, that give more information.. (d) How are maps more helpful than a globe? Answer. In the maps more information can be given about a place, through scale, symbols and names of more places. On a globe only the name of a country and its capital city can be given. Therefore, maps are more useful than a globe. (e) Distinguish between a map and a plan. Answer. A map is an accurate picture of a place giving distance, direction and other information through symbols. A plan is a drawing of a small area on a large scale. A plan is a sub unit of a large scale map. (f) Which map provides detailed information? Answer. Thematic maps provide detailed information. 10x10learning.com Page 8
(g) How do symbols help in reading maps? Answer. There is an international agreement about the use of conventional symbols and colours in maps. Therefore, the symbols are common for all maps published for any country in the world. This makes it easier to read a map and get the information required about any place across the globe. 2. Tick the correct answers. Here the answer is given in colour (a) Maps showing distribution of forests are (i) Physical map (ii) Thematic Map (iii) Political map (b) The blue colour is used for showing (i) Water bodies (ii) Mountains (iii) Plains (c) A compass is used (i) To show symbols (ii) To find the main direction (iii) To measure distance (d) A scale is necessary (i) For a map (ii) For a sketch (iii) For symbols 10x10learning.com Page 9