Geography 6. Global: Latitudes & Longitudes

Globe is a true model (miniature form) of the earth.

Geographical Axis - The axis on which earths rotates. North Pole lies on the north and South Pole lies on the south.

Equator – An imaginary line running across the globe that divides earth into two hemispheres. Northern half of the earth is Northern Hemisphere and southern half is Southern Hemisphere.

Parallels of Latitude - All parallel circles from the equator up to the poles.

The equator represents the 0° latitude.

Since the distance from the equator to either of the poles is one-fourth of a circle round the earth, it’ll measure 1/4^th of 360°, i.e. 90°. Thus, 90°N latitude marks the North Pole and 90°S latitude marks the South Pole.

All parallels north of the equator are called North Latitudes.

All parallels south of the equator are called South Latitudes.

 

By measuring the angle of the Pole Star from your place, you can know the latitude of your place.

IMPORTANT PARALLELS OF LATITUDES

Besides the equator (0°), the North Pole (90°N) and the South Pole (90°S), there are four important parallels of latitudes–

(i)             Tropic of Cancer (23 ½°N) in the Northern Hemisphere.

(ii)           Tropic of Capricorn (23 ½°S) in the Southern Hemisphere.

(iii)          Arctic Circle at 66 ½°N of the equator.

(iv)          Antarctic Circle at 66 ½°S of the equator.

                                  

HEAT ZONES OF THE EARTH

(i)       Torrid Zone - The mid-day sun is exactly overhead at least once a year on all latitudes in between the Tropic of Cancer and the Tropic of Capricorn. This area, therefore, receives the maximum heat.

(ii)     Temperate Zones - The mid-day sun never shines overhead on any latitude beyond the Tropic of Cancer and the Tropic of Capricorn. The angle of the sun’s rays goes on decreasing towards the poles. The areas bounded by the Tropic of Cancer and the Arctic Circle in the Northern Hemisphere, and the Tropic of Capricorn and the Antarctic Circle in the Southern Hemisphere, have moderate temperatures.

(iii)    Frigid Zones - Areas lying between the Arctic Circle and the North Pole in the Northern Hemisphere and the Antarctic Circle and the South Pole in the Southern Hemisphere, are very cold. It’s because here the sun doesn’t rise much above the horizon. Therefore, its rays are always slanting and provide less heat.

 

Longitude – Imaginary lines of references running from North Pole to South Pole are called Meridians of Longitude. 

The distances between them are measured in degrees of longitude. Each degree is further divided into minutes, and minutes into seconds. 

They’re semicircles and the distance between them decreases steadily poleward until it becomes zero at the poles, where all the meridians meet.

Unlike parallels of latitude, all meridians are of equal length. Thus, it was difficult to number the meridians. Hence, all countries decided that the count should begin from the meridian which passed through Greenwich, where the British Royal Observatory is located. This meridian is called the Prime Meridian. Its value is 0° longitude and from it we count 180° eastward as well as 180° westward. The Prime Meridian and 180° meridian divide the earth into two equal halves, the Eastern Hemisphere and the Western Hemisphere. 180°E and 180°W meridians are on the same line.

LONGITUDE AND TIME

The best means of measuring time is by the movement of the earth, the moon and the planets. The sun regularly rises and sets every day, and naturally, it’s the best time-keeper throughout the world. Local time can be reckoned by the shadow cast by the sun, which is the shortest at noon and longest at sunrise and sunset.

As the earth rotates from west to east, those places east of Greenwich will be ahead of Greenwich Time and those to the west will stand behind it.

The rate of difference can be calculated as follows.

The earth rotates 360° in about 24 hours, which means 15° an hour or 1° in 4 minutes. 

Thus, when it’s 12 noon at Greenwich, the time at 15° east of Greenwich will be 15x4 = 60 minutes, i.e., 1 hour ahead of Greenwich Time, which means 1 p.m. 

But at 15° west of Greenwich, the time will be behind Greenwich time by one hour, i.e., it’ll be 11.00 a.m. Similarly, at 180°, it’ll be midnight when it’s 12 noon at Greenwich.

All the places on a given meridian of longitude have the same local time.

 

Why Do We Have Standard Time?

The local time of places which are on different meridians is bound to differ. For example, it’ll be difficult to prepare a time-table for trains which cross several longitudes.

In India, for instance, there will be a difference of about 1 hour and 45 minutes in the local times of Dwarka in Gujarat and Dibrugarh in Assam. It’s, therefore, necessary to adopt the local time of some central meridian of a country as the standard time for the country. In India, the longitude of 82 ½°E (82° 30'E) is treated as the standard meridian. The local time at this meridian is taken as the standard time for the whole country. It’s known as the Indian Standard Time (IST). The meridian of longitude is termed as Standard Meridian of India.

Some countries have a great longitudinal extent and so they have adopted more than one standard time.

The earth has been divided into 24 time zones of one hour each. Each zone thus covers 15° of longitude.

Russia has 11, USA and Canada has 6 time zones.