Globe

Unit 2

GLOBE

Learning Objectives

• To understand the four cardinal directions.

• To learn about the shape of the Earth.

• To understand about the model of the Earth - the globe.

• To understand the significance of lines of latitudes and longitudes.

• To know how standard time is calculated around the world.

Surya and Poovendhan are very good friends who study in the sixth standard and live in a beautiful village called Thirunandriyur. Surya lives in South Street, while Poovendhan lives in North Street. Every day they go to school together. One day.........

Surya: Why are you coming so late, Poovendha?

Poovendhan: Please bear with me, Surya! Come, let’s go.

Surya: What took you so long?

Poovendhan: You live on South Street. But, I have to come from the North Street, which is so far away from here. That’s why I’m late.

Surya: Yes, that’s true. But wherever we live, don’t you remember that we all live on planet Earth?

Poovendhan: Yes! Yes! I do remember, Even our Ponni Miss taught us about the Solar System.

Surya: But, I have a doubt ….

Poovendhan: Tell me, what is it?

Surya: We can see our house, the things around us, the people, animals and birds with our eyes. But, why can’t we see our Earth as a whole?

Poovendhan: Haven’t you seen it?

Surya: No, I haven’t. Have you ever seen it?

Poovendhan: Yes, in our school only.

Surya: Did you say, in our school?

Poovendhan: Yes, on our Ponni Miss’ table. Big and spherical!

Surya: Oh! Yes! Like a ball on a stand?

Poovendhan: Exactly! That is our Earth

Surya: But........ But, our teacher said that our Earth is in the Milky Way Galaxy. But you say that our Earth is on our teacher’s table. I am so confused. Come, let’s go and ask Ponni Miss.

The bell rang as they reached school. They attended the morning assembly and went to the classroom. During the social science period, Surya asks Ponni Miss to clear his doubts.

Surya: Good morning, Miss.

Teacher: Good morning.

Surya: Madam, you told us on the other day that our Earth is in the Milky Way galaxy.

Teacher: Yes, it is true. This is the model of the Earth.

Surya: A model of the earth, Madam? Please explain!

Teacher: Sure, Surya.

The teacher asks all the students to sit down and starts explaining.

Directions

The directions on the ground are always shown with respect to the North. If we know the North, then it is easy to find the other directions, namely South, East and West. These are the four cardinal directions.

We know that the Sun rises in the East and sets in the West. If we stand facing the sun in the morning, then we face the east. The west is towards our back. The left hand points towards the north and the right hand points towards the south. We should always keep this in mind.

Globe

We live on the planet Earth, which is found third from the Sun. Since the Earth is huge and we live on a very small area, we are not able to see the Earth as a whole. But, when we travel to space, we can see the Earth as a whole.

So, in order to see the shape of the Earth as a whole and to know its unique features, a three dimensional model of the Earth was created with a specific scale.

The surface area of the Earth is 510.1 million square kilometres.

The Earth which is spherical, is flat at the poles and bulges at the Equator. The Earth cannot be compared with any other geometrical shape as it has a very unique shape. Hence, its shape is called a geoid (earth shaped)

The Earth moves around the Sun. It also rotates from the West to East on its axis at an inclination of 23 ½°. The globe is also inclined at an angle of 23 ½°. The axis is an imaginary line. It is not actually found on the Earth.

* The first globe was created by the Greeks in the year 150 AD(CE).

* The Indian astronomer Aryabhatta - I has mentioned in his book. ‘Aryabhatta Sidhantha’. ‘The stars in the sky seem to move towards the West because of the Earth’s roation on its axis’.

Lines on the Globe

There are imaginary lines which are drawn on the globe horizontally and vertically to find a location and calculate distance and time. These imaginary lines are called lines of latitudes and longitudes.

Ptolemy, a Greco – Roman mathematician, astronomer and geographer, was the first person to draw the lines of latitude and longitude on a map.

In his book, ‘Geographia’ a detailed description about the Earth’s surface, its size and circumference and many locations based on the lines of latitude and longitude are given.

Latitudes

The imaginary lines which are drawn horizontally on East - West direction on the Earth are called the lines or parallels of latitudes. The 0° line of latitude which divides the Earth into two halves is known as the Equator. From the Equator, parallel lines are drawn towards the North and South poles at equal intervals. The latitudinal extent between 1° line of latitude on Earth is 111 km.

Since the Earth is geoid shaped, the length of the lines of latitude decreases from the Equator towards the South and North Poles. The 90° North and South Poles are not found as lines, but as points.

The lines of latitude that are drawn horizontally between the Equator and the North Pole are called ‘Northern latitudes’ and those which are found between the Equator and the South Pole are called ‘Southern Latitudes’. The lines of latitude consist of 89 parallels in the Northern Hemisphere and 89 parallels in the Southern Hemisphere, one at the Equator and the two poles are found as points. Totally, there are 181 parallels found on earth.

The Equator is the longest of all lines of latitude. Hence, it is also known as ‘The Great Circle’.

Activity :

Draw a circle on a paper. Draw a horizontal line across the middle of a circle. Keeping this line as 0°,  draw lines on both sides with an equal interval of 15° with the help of a protractor. The lines you have drawn are lines of latitudes.

Northern Hemisphere

The area of the Earth from the equator (0°) to the South Pole (90°S) is called the Southern Hemisphere.

Southern Hemisphere

The area of the Earth from the equator (0°) to the South Pole (90°S) is called the Southern Hemisphere.

The location of any country or place is based on this division of the hemispheres

HOTS

Based on the latitudinal extent, in which hemisphere is India located?

Important lines of latitude

The earth rotates on its axis at an inclination of 23½°. It also revolves around the sun while rotating. Based on the angle at which the sun’s rays fall on the earth, certain lines of latitude gain significance.

• 0°N and S – 23½°N and S lines of latitudes are called – Low latitudes

• 23½°N and S – 66½°N and S lines of latitudes are called – Middle Latitudes

• 66½°N and S – 90°N and S lines of latitudes are called –High Latitudes

(Source : A Dictionary of Geography – Susan Mayhew, Oxford University Press,   Fifth edition -2015)

The Sun’s rays do not fall equally on all parts of the earth. They fall vertically over the Equator and slanting towards the poles. Thus, all the places on earth do not have the same amount of temperature. Based on the amount of heat received from the Sun, the lines of latitude help in dividing the earth into different climatic zones.

Torrid Zone

The region from the Equator towards the Tropic of Cancer (23½°N) and the Tropic of Capricorn (23½°S) is called the Torrid Zone. The Sun’s rays fall vertically over this region and the average temperature is very high. Hence this region is known as the Torrid Zone.

Temperate Zone

From the Tropic of Cancer (23½°N) to the Arctic Circle (66½°N) and from the Tropic of Capricorn (23½°S) to the Antarctic Circle (66½°S), the Sun’s rays fall slantingly. Moderate temperature prevails in this region. Hence, this region is called Temperate Zone.

Frigid Zone

From the Arctic Circle (66½°N) to the North Pole (900N) and from the Antarctic Circle (66½°S) to the South Pole (90°S), the Sun’s rays fall further inclined, through out the year. The temperature is very low. Hence, this region is known as Frigid Zone.

Some lines of latitude are also called by the following names in Tamil.

Latitude –  ahalangu   (அகலாங்கு)

Longitude – nettangu (நெட்டாங்கு)

Equator - nilanaduvarai (நிலநடுவரை)

Tropic of Cancer - kadagavarai (கடகவரை)

Tropic of Capricorn - magaravarai (மகரவரை)

(Source: Ariviyal Kalanjiyam, The Tamil University)

Longitudes

The imaginary lines drawn vertically connecting the North Pole and the South Pole are called lines or meridians of longitude. These lines of longitude are seen as semi circles. The 0° line of  longitude is called the Prime Meridian. There are 180 lines of longitude towards the East and West from the Prime Meridian. So, there are totally 360 lines of longitude. These lines converge at the poles. The 180° W and 180° E line of longitude are the same line.

The lines of longitude that are found between the Prime Meridian and the 180° East line of longitude are called ‘Eastern Longitudes’ and the lines of longitude that are found between the Prime Meridian (0°) and the 180° West line of longitude are called ‘Western Longitudes’. Two opposite meridians form a great circle

The lines of longitude are found as semi circles covering 111 km at the Equator, 79 km at 45° latitude and no space between the lines at the poles.

Activity :

Take a ball and a thin iron wire. Pierce the ball with the wire from one end to the other end through the middle. Remove the wire. Draw circles around the points. Name the northern most point as North Pole and the southern most point as South Pole. The angle of a circle is 360°. Mark points on the circle at an interval of 15° using a protractor. Then draw lines joining these points on the top and bottom of the ball. The lines that you have drawn are lines of longitudes.

Eastern Hemisphere

The part of the Earth between the 0° line of longitude and the 180° East line of longitude is known as the Eastern Hemisphere.

Western Hemisphere

The part of the Earth from 0° line of longitude to 180° West line of longitude is called as Western Hemisphere.

Activity

Based on the longitudinal extent, in which hemisphere is our country located? Look at the globe and answer.

Significant Lines of Longitude

Greenwich Meridian

The Royal Astronomical Observatory is located at Greenwich near London in England. According to the International Meridian Conference held in 1884 in Washington DC in the U.S.A. all nations agreed on choosing the Greenwich Meridian as the international standard meridian (0°). 

This line of longitude is called the Prime Meridian and it is also known as the Greenwich Meridian because it passes through Greenwich.

International Date Line

The 180º line of longitude has been fixed as the International Date Line, drawn on the Pacific Ocean between Alaska and Russia through Bering Strait. If a person crosses this line from the West to East, he loses a day. On the other hand, when he crosses from the East to West, he gains a day. Based on this, the date is fixed for different countries or regions of the world.

The International  Date Line is not straight.  If the line is drawn straight, two places in the same country would have different dates.  So the International Date  Line  is  found  zigzag  in  certain places to avoid confusion.

Earth Grid

The imaginary lines of latitude and longitude form a grid like pattern on the surface of the earth, known as the ‘Earth grid’ or ‘Geographic grid’.

To locate a place exactly on earth, the latitudinal and longitudinal extensions are required.

Longitude and Time

As many as 360 lines of longitude are drawn to connect the North and South Poles around the Earth 180° on the Eastern Hemisphere and 180° on the Western Hemisphere. Time is calculated on the basis of the lines of longitude.

Fact

 * The Earth takes one day to rotate on its axis.

 * 1 day = 24 hours

* 1 hour = 60 minutes

* 24 hours = 24 x 60 = 1440 minutes

* The angle of the earth = 360°

* 360° = 360 Longitudes

* 360° = 1440 minutes

* So 1° = 1440/360 = 4 minutes

* In 4 minutes = 1° rotation

* In 60 minutes = 60/4 = 15°rotation

* So, in an hour (60 minutes) the earth rotates 15°

Local Time

When the sun is overhead on a particular line of longitude, it is 12 noon at all the places located on that line of longitude. This is called local time.

The Sun is overhead on a line of longitude only once in a day. So the local time differs for every line of longitude.

When the Sun is overhead the Greenwich Meridian at 12 noon, it is the local time of that place. The world time is calculated by this standard line of longitude. It is known as the Greenwich Mean Time (GMT).

For example, if the time is 12 noon at Greenwich Meridian, it is 12:04 p.m. at 1°E line of longitude and 11:56 a.m. at 1°W line of longitude. So, as one moves towards the east from any meridian the time increases. And if one moves towards the west from any meridian, time decreases.

1. The word meridian is derived from the Latin word ‘Meridianus’. It means mid day. (Medius – Middle, dies – day). So, meridian means the position of the Sun found overhead at a place at noon.

2. a.m. means 'anti Meridiem' (anti – before) – Before Noon.

3. p.m. means 'post Meridiem' (Post after/later) – After noon.

Standard Time

Local time is calculated when the sun is overhead at noon. Many lines of longitude may pass through a country. Countries may or may not observe a common time. The standard time of a country or a part of it is calculated keeping a particular meridian as a standard one.

The meridians are selected in multiples of 15° or 7 ½°. It is done in such a way that the variation of standard time from the Greenwich is expressed either as 1 hour or ½ an hour.

Indian Standard Time

The longitudinal extent of India is from 68°7’ E to 97°25’ E. As many as twenty nine lines of longitude pass through India. Having 29 standard time is not logical. Hence 82½° E line of longitude is observed as the Prime Meridian to calculate the Indian Standard Time (IST).

The 82½° E line of longitude passes throughMirzapur near Allahabad in Uttar Pradesh. This is located at an equal distance from Ghuar Mota in Gujarat and Kibithu in Arunachal Pradesh.

Time Zones

The world has 24 time zones. Some countries have a great longitudinal extent. So they have more than one standard time. Example: Russia has 7 time zones.

Activity:

1. What is the difference in time between the GMT and IST?

2. If it is 5 a.m. at New York City, USA. what would be the time at NewDelhi, the capital of India?

3. If it is 12 Midnight at London, what would be the time in India?

4. The standard time of Sydney city in Australia is found to be at a difference of _________ hours from that of the GMT.

5. Mr. Senthamizh travels by flight from Chennai to London. He boarded the aeroplane at 9a.m After 12 hours of travel, at what time (GMT) would he have reach London?

We saw about the lines of latitude and longitude drawn on the globe. Besides these, physical land forms, seas, oceans, countries etc., are also found on the globe

Wrap up

1. The imaginary lines drawn horizontally from the East to West on the globe and maps are called lines of latitude or parallels.

2. The imaginary lines drawn vertically from the North to South on the globe and maps are known as lines of longitude or meridians.

3. The 0° line of latitude is called theEquator.

4. The 0° line of longitude is called the Greenwich Meridian or the Prime Meridian.

5. The part of the Earth from the Equator (0°) to North Pole (90°) is called the Northern Hemisphere and from the Equator (0°) to South Pole (90°) is called the Southern Hemisphere.

6. The part of the Earth from the Greenwich Meridian (0°) to 180° East line of longitude is called the Eastern Hemisphere and from Equator (0°) to 180° West line of longitude is called the Western Hemisphere.

7. Lines of latitude are circles which are drawn at a distance of about 111 km. The poles are shown as points.

8. Lines of longitude are drawn as semi circles. The distance between the lines of longitude at the Equator is 111 km. It is found at a distance of 79 km at 45° latitude and they converge at the poles.

9. Lines of latitude do not merge, while lines of longitude converge at the poles.

10. Time is calculated on the basis of the lines of longitude. The 180° line of longitude is the International Date Line.

Glossary

1. Globe – A model of the earth

2. Lines of Latitude / Parallels– Imaginary lines drawn horizontally on the Earth from the East to West

3. Lines of Longitude / Meridians – Imaginary line drawn vertically on the Earth from the North to South

4. Geoid – The shape of the Earth

5. Hemisphere – Dividing the earth on the basis of 0° lines of latitude and longitude with regard to directions

6. Equator– The line of latitude drawn horizontally at the centre of theEarth

7. Tropic of Cancer – 23 ½° N line of latitude

8. Tropic of Capricorn – 23 ½° S line of latitude

9. Arctic Circle – 66 ½° N line of latitude

10. AntarcticCircle– 66 ½° S line of latitude

Reference

1. Goh Cheng Leong, Certificate Physical and Human Geography (2009), Oxford University Press, New Delhi, India.

2. A Dictionary of Geography – Susan Mayhew, Oxford University Press, Fifth edition -2015.

3. அறிவியல் களஞ்சியம் (தொகுதிகள்), தஞ்சை தமிழ்ப்பல்கலைக்க வெளியீடு.

4. The earth shape and gravity (1965) Oxford Degman Press.

5. Strahler, Physical Geopraphy 4th Edition (1965) New York MC Graw – Hill Book Co.

Web Links

1. https://www.britannica.com

2. https://www.latlong.net

ICT CORNER

Geography - Globe

Through this activity you will know about the globemodel!.

Steps:

Step -1 Use the URL or scan the QR code to open the activity page.

Step -2 Click the red “hot spot” area to see the main landmarks of the globe.

Step -3 In the view box Click the “Core” option to view the Earth's inner layers.

Step -4 Drag and rotate the Globe you can rotate the Globe.

*Pictures are indicatives only.

Browse in the link

Web: https://solarsystem.nasa.gov/planets/earth/overview/ (or) scan the QR Code