Latitudes
To find a friend’s house in a village we use the road and house number. To find any place on the Earth in the same way, imaginary horizontal and vertical lines are drawn on the globe.
Latitude is the angle a place makes with the equatorial plane at the centre of the Earth. The imaginary horizontal circles through places with the same angle are called latitudes, and their value is given in degrees.
Key idea 1 : How is the angle measured? — The angle that the line joining a place with the centre of the Earth makes with the equatorial plane is the latitude of that place. In the northern hemisphere 30° North means 30 degrees north of the equator; in the south, 30° South. All latitudes are parallel to each other.
Key idea 2 : Equator and hemispheres — The 0° latitude is the equator; it is called the base latitude or the Great Circle. It divides the Earth into two equal parts: the northern hemisphere and the southern hemisphere. From the equator towards the poles the value of latitude increases and the size of the circles becomes smaller.
Key idea 3 : Important latitudes — Tropic of Cancer 23°30′ N, Tropic of Capricorn 23°30′ S, Arctic Circle 66°30′ N, Antarctic Circle 66°30′ S, North Pole 90° N and South Pole 90° S. At an interval of 1° a total of 181 latitudes can be drawn on the Earth, and the distance between two consecutive latitudes is about 111 km everywhere.
- Easy : Name of the 0° latitude? — Equator.
- Medium : Where is the Tropic of Cancer? — 23°30′ N.
- Exam-type : Latitude at the poles? — 90°.
In the figure: Main values of latitude.
0, 23½, 66½, 90.
All latitudes are not of equal length; the equator is the largest and circles become smaller towards the poles.
Memory clue: Akshansh = horizontal. Horizontal lines = latitudes. Memory clue: "Equator big, poles small".
Spot the difference
| Latitude | Value | Note |
|---|---|---|
| Equator | 0° | Two hemispheres |
| Tropic of Cancer | 23°30′ N | Passes through India |
| Arctic Circle | 66°30′ N | Near the North Pole |
Practice questions
- 1What is latitude?
- 2Why is the equator called the base latitude?
- 3Write four important latitudes and their values.
- 4How many latitudes can be drawn at 1° interval on the Earth?
- 5What is the distance between two consecutive latitudes?
- 6Why does the size of latitudes become smaller towards the poles?
- 7How are latitudes written in the northern and southern hemispheres?
- 8Show the Tropic of Cancer and Tropic of Capricorn on a globe.
Show answers (try them yourself first)
- 1The angle made with the equatorial plane at the centre.
- 2All latitudes are measured from it.
- 3Equator 0°, Tropic of Cancer 23°30′ N, Capricorn 23°30′ S, poles 90°.
- 4181.
- 5About 111 km.
- 6Because the radius of the circle decreases.
- 730° N and 30° S.
- 8Student shows on the globe.
Longitudes
Latitude tells the north-south position, but many places lie on the same latitude. To tell the exact place among them another kind of lines is needed, which are longitudes.
Longitudes are a series of imaginary semicircles joining the North Pole to the South Pole. They are drawn by measuring angles at 1° interval on the equatorial plane east and west of the 0° longitude (base longitude).
Key idea 1 : Base longitude and hemispheres — The 0° longitude is the base longitude. The 180° longitude comes exactly opposite it. Together they form a circle dividing the Earth into the eastern and western hemispheres. In the eastern hemisphere we write ‘10° East’, in the western ‘10° West’.
Key idea 2 : Number and distance of longitudes — At 1° interval a total of 360 longitudes can be drawn. All of them meet at the poles. The distance between two consecutive longitudes is about 111 km at the equator and decreases towards the poles, becoming zero at the pole.
Key idea 3 : Difference between latitudes and longitudes — Latitudes are full circles, parallel to each other and of different sizes; longitudes are semicircles, all of equal length, and meet at the poles. Latitudes and longitudes cut each other at right angles.
- Easy : Name of the 0° longitude? — Base longitude.
- Medium : Where is the 180° longitude? — Opposite to 0°.
- Exam-type : Where do longitudes meet? — At the poles.
In the figure: The method of drawing longitudes.
0° and 180° = one circle.
The distance between longitudes is not 111 km everywhere; it is 111 km only at the equator and decreases towards the poles.
Memory clue: Longitude = vertical semicircle, meeting at the poles. Memory clue: "Vertical line = Rekhansh".
Spot the difference
| Point | Latitudes | Longitudes |
|---|---|---|
| Shape | Full circles | Semicircles |
| Direction | East-west (horizontal) | North-south (vertical) |
| Number (1° apart) | 181 | 360 |
Practice questions
- 1What are longitudes?
- 2Which hemispheres are formed by 0° and 180° longitudes?
- 3How many longitudes can be drawn at 1° interval on the Earth?
- 4What is the distance between longitudes at the equator and at the pole?
- 5Write three differences between latitudes and longitudes.
- 6At which angle do latitudes and longitudes cut?
- 7How are longitudes written? Give two examples.
- 8Show 0°, 90° East and 90° West longitudes on the globe.
Show answers (try them yourself first)
- 1Imaginary semicircles joining the poles.
- 2Eastern and western hemispheres.
- 3360.
- 4About 111 km at the equator; zero at the pole.
- 5Shape, direction and number differ; see the table.
- 6At right angles.
- 710° East and 120° West.
- 8Student shows on the globe.
Graticule and finding a location
In a cinema hall we get ‘row 5, seat 7’ and find our seat easily. On the Earth latitudes and longitudes together form a similar net.
The net formed by latitudes and longitudes is called a graticule. With it any place on the Earth can be fixed by two numbers: latitude and longitude.
Key idea 1 : Degrees, minutes, seconds — The distance between two consecutive latitudes is 111 km, so degrees are divided into smaller parts to tell places in between. 1 degree = 60 minutes (′) and 1 minute = 60 seconds (″). The minutes and seconds here are not units of time but units of measuring angles.
Key idea 2 : How to find a location — First we see the latitude (north or south) of the place, then the longitude (east or west). The point where the two cross is the place. E.g. ‘19° North, 73° East’ is a place in the western part of India.
Key idea 3 : Uses of graticule — In today’s world the graticule is used for ships, aircraft, maps and GPS in mobile phones. A place can be told without mistake with the same latitude and longitude, so it is accepted all over the world.
- Easy : 1 degree = how many minutes? — 60.
- Medium : 1 minute = how many seconds? — 60.
- Exam-type : How many numbers to tell a place? — Two (latitude, longitude).
In the figure: The graticule of latitudes and longitudes.
The world’s largest rotating globe ‘Eartha’ is at Yarmouth in Maine, USA; its diameter is about 12.5 m (41 ft) and Guinness World Records recognised it in 1999 (as per several sources; check with the book).
1° = 60′; 1′ = 60″.
The minutes and seconds here are not clock time; they are units of angle.
Memory clue: Latitude + longitude = address. Memory clue: "Horizontal and vertical make the net".
Spot the difference
| Unit | Symbol | Value |
|---|---|---|
| Degree | ° | 60 minutes |
| Minute | ′ | 60 seconds |
| Second | ″ | Smallest |
Practice questions
- 1What is a graticule?
- 2State the relation between degree, minute and second.
- 3What is the use of a graticule?
- 4How is a place found from latitude and longitude?
- 5Why are minute and second not units of time here?
- 6Name two things at home or around you like a graticule.
- 7Observing a 15° graticule on a map, tell through which continents the 0° longitude passes.
- 8Using a globe and map find the latitude and longitude of your district.
Show answers (try them yourself first)
- 1The net formed by latitudes and longitudes.
- 21° = 60′; 1′ = 60″.
- 3Finding locations for ships, aircraft, maps, GPS.
- 4The crossing point of latitude and longitude.
- 5They are units of measuring angle.
- 6E.g. a chessboard, a woven cloth net; student writes own.
- 70° longitude passes through Europe, Africa and Antarctica (check on the map).
- 8Student finds on own.
Standard time and Indian Standard Time
When it is 9 am in Mumbai it is half past three in the early morning in London. The Sun is not overhead at the same time everywhere, so time differs around the world.
The 0° longitude is called the Prime Meridian; it passes through Greenwich, a town near London in England. Its time is the Global Standard Time (GMT) and UTC time is also used.
Key idea 1 : Indian Standard Time — The 82°30′ East longitude, which passes near Mirzapur in Uttar Pradesh, is India’s standard meridian. From it the Indian Standard Time (IST) is fixed, which is 5 hours 30 minutes ahead of Greenwich Mean Time.
Key idea 2 : Ancient India’s base longitude — Before Greenwich was considered the base longitude India had its own base longitude, passing near Ujjayini (Ujjain). About 1500 years ago astronomers like Varahamihira lived and studied there. It was taken as the base for time calculation, positions of planets and maps.
Key idea 3 : Satellite service: NavIC — India uses a system of its own seven satellites called IRNSS (Indian Regional Navigation Satellite System). It provides accurate location, time and navigation services in India and up to about 1500 km beyond its borders.
- Easy : How many degrees does the Earth rotate in 24 hours? — 360°.
- Medium : Time difference per 1° of longitude? — 4 minutes.
- Exam-type : IST is how much ahead of GMT? — 5 hours 30 minutes.
In the figure: Standard time from longitude.
As per several sources: the ‘Surya Siddhanta’ lists Ujjain as a place on the zero meridian; Ujjain is at about 23°11′ N and 75°46′ E, that is near the Tropic of Cancer but not on it; ‘23°30′ N’ in the textbook figure is the value of the Tropic of Cancer (as per several sources; check with the book).
The NavIC satellite system has seven satellites and covers India and about 1500 km beyond the borders; it is considered operational since 2018 (as per several sources; check with the book).
82½° × 4 min = 330 min = 5 h 30 min.
Greenwich (0°) is not India’s standard meridian; India’s standard meridian is 82°30′ East.
Memory clue: Greenwich 0° = GMT; India = GMT + 5:30. Memory clue: "Eastwards, time moves ahead".
Spot the difference
| Point | Global | India |
|---|---|---|
| Standard meridian | 0° Greenwich | 82°30′ E |
| Name of time | GMT / UTC | IST |
| Difference from GMT | 0 | +5 h 30 min |
Practice questions
- 1What is the Prime Meridian?
- 2What is GMT? From which place is it fixed?
- 3Which is India’s standard meridian and where does it pass?
- 4State the difference between IST and GMT.
- 5What is the time difference per 15° of longitude and why?
- 6How do we get 5 hours 30 minutes from 82°30′ East?
- 7Near which city did ancient India’s base longitude pass?
- 8Write about NavIC.
Show answers (try them yourself first)
- 10° longitude; passes through Greenwich.
- 2Greenwich Mean Time; from Greenwich.
- 382°30′ E; near Mirzapur.
- 4IST = GMT + 5 h 30 min.
- 51 hour; because the Earth rotates 360° in 24 hours.
- 682.5 × 4 = 330 minutes = 5 h 30 min.
- 7Ujjain (Ujjayini).
- 8Seven satellites; location-time-navigation in India and 1500 km around.