We draw latitudes and longitudes across the globe to locate places on it. Imaginary lines running east to west, parallel to the Equator, are known as lines of latitude. Imaginary lines running north to south, across the poles, are known as lines of longitude. The framework formed by the intersection of the latitudes and longitudes on the Earth is known as a geographic grid. It helps us to locate exact places on the globe.
Lines of Longitude
Main characteristics of longitudes
- The vertical lines which run from the North Pole to the South Pole are called longitudes or the meridians of longitudes.
- It is not possible to find the exact location of a place only on the basis of latitudes. We also have to take into account the longitudes.
- The distance between two longitudes is measured in terms of degrees. Longitudes are semi-circular and the distance between them decreases as they go towards the poles. The distance between two lines of longitude is maximum at the Equator (111 km). The two diametrically opposite lines which make a full circle is also known as a great circle.
- The Prime Meridian is a 0° longitude which passes through the British Royal Observatory at London. It divides the Earth into the Western Hemisphere and the Eastern Hemisphere.
- When the latitudes and longitudes criss-cross each other at right angles, they form a geographical grid or coordinate which helps us to find the exact location of a place.
Longitude and Time
- As the Earth completes one rotation from west to east in 24 hours, every meridian gets direct sunlight from the Sun once every day.
- The Earth has been divided into twenty-four time zones of one hour each. Each zone thus covers 15° of longitude. 1° of longitude is covered in 4 minutes. Different heat zones of the Earth Distance between all the longitudes becomes zero at the poles
- When the Greenwich meridian gets direct sunlight, the places located along it have mid-day. As the Earth rotates from west to east, the places which are located to the east of the Greenwich meridian are ahead of Greenwich time.
- In the same way, the places located to the west of Greenwich are behind Greenwich time. So, to find the local time of a place, for each 1° of longitude towards the east, 4 minutes are added and for each 1° of longitude towards the west, 4 minutes are subtracted.
Indian Standard Time
The local time of a place depends on the longitude which passes through it. Many longitudes pass through India. Therefore, the standard time for each country is usually taken as the time of the central meridian which passes through it. In India, 82 ½ °E longitude determines the standard time. This is known as Indian Standard Time. This longitude passes through Allahabad in Uttar Pradesh.
- We can calculate the time of two different places with the help of their longitudes. Lucknow is located at 82° E and London is located at 0° GMT.
- Because the Earth rotates from west to east, places which lie to the east of Greenwich are ahead of places that lie to the west of Greenwich. The Earth rotates 1° in 4 minutes. Thus, if Lucknow is located in the east of Greenwich at 82°E, we will multiply 82 by 4 which will be 328 minutes or 5 hours and 28 minutes. Therefore, the time at Lucknow is 5 hours and 28 minutes ahead of London (since Lucknow is located to the east of Greenwich). So, if the time in London is 12:00 pm, we will add 5 hours and 28 minutes to it, which will be 5:28 in the evening.
- Therefore, it will be 5:28 pm at Lucknow in the evening when it is 12:00 pm in London.
Also, Read The Earth’s Grid