Standard Time and Time Zones

If each town were to keep the time of its own meridian, there would be much difference in local time between one town and the other. At 10.00 a.m. in Kota Bharu (a difference of 2 and half degrees in longitude). In larger countries such as canada, U.S.A., China and U.S.S.R. the confusion arising from time differences alone would drive people mad. Travellers going from one end of the country to the other would have to keep changing their watches if they wanted to keep their appointments. This is impracticable and very inconvenient.
To avoid all these difficulties, a system of standard time is observed by all countries. Most countries adopt their standard time from the central meridian of their countries. The Nigerian government has accepted the meridian of 15 degrees east for the standard time which is one hour ahead of Greenwich Mean Time. The whole world has in fact been divided into 24 Standard Time Zones, each of which differs from the next by 15 degrees in longitude or one hour in time. Most countries adhere to this division but due to the perculiar shapes and locations of some countries, reasonable deviations from the Standard Time Zones cannot be avoided.
Larger countries like U.S.A., Canada and U.S.S.R., which have a great east-west stretch, have to adopt several time zones for practical purposes. U.S.S.R., which extends through almost 165 degrees of longitude, is divided into eleven time zones. When it is 10.00 p.m. on Monday night in Leningrad, it will be almost 7.00 a.m. the following Tuesday morning in Vladivostock. Travellers along the Trans-Siberian Railway have to adjust their watches almost a dozen times before they reach their destination. Both Canada and U.S.A. have five time zones - the Atlantic, Eastern, Central, Mountain and Pacific Time Zones. The difference between the local time of the Atlantic anad Pacific coasts is nearly five hours.

The International Date Line

A traveller going eastwards gains time from Greenwich until he reaches the meridian 180 degrees east when he will be 12 hours ahead of G.M.T. Similarly in going westwards, he loses 12 hours when he reaches 180 degrees west. There is thus a total difference of 24 hours or a whole day between the two sides of the 180 degrees meridian. This is the International Date Line where the date changes by exactly one day when it is crossed. A traveller crossing the date line from east to west loses a whole day (because of the loss in time he has made); and while crossing the date line from west to east he gains a day (because of the gain in time he encountered). Thus when it is midnight, Friday on the Asiatic side, by crossing the line eastwards, he gains a day; it will be midnight Thursday on the American side, i.e. he experiences the same calender date twice! When Magellan's ship eventually arrived home in Spain in 1522 after circumnavigating the world from the Atlantic Ocean to the Pacific Ocean and westwards across the International Date Line, the crew knew nothing about adding a day for the one they had missed. They thought they had arrived on the 5 September. They were shocked to be told that the date was 6 September. A modern aircraft leaving Wellington at 5.00 p.m. on Friday reaches Hawaii, 6601 km away, at 2.00 p.m. the same Friday. The same aircraft on its return journey from Hawaii at 11.00 a.m. on Sunday. Can you explain this?
The International Date Line in the mid-Pacific curves from the normal 180 degrees meridian at the Bering Strait, Tonga and other islands to prevent confusion of day and date in some of the island groups that are cut through by the meridian. Some of them keep Asiatic or New Zealand standard time, others follow the American date and time. To find local time in two places on opposite sides of the International Date Line remember that crossing the 'line' going eastwards a whole day is gained. Crossing the 'line' going westwards a whole day is lost.
Example. If someone in Tokyo (time zone 135 degrees east) telephones a friend in Vancouver on 4 December at 10.00 a.m. what time will his friend receive the call in Vancouver (time zone 120 degrees west)?
1. Longitude difference 180' - 135'E = 45'; 180' - 120'W = 60'; 45' + 60' = 105'
2. Therefore time difference = 105/15 = 7 hours.
3. Vancouver is east of Tokyo, therefore time goes on 7 hours.
4. Going eastwards across I.D.L. a whole day is gained. Therefore the time in Vancouver is 5.00 p.m. on 3 December.

Great Circle Routes

Since the earth is spherical in shape, the shortest distance between any two points on the globe lies along its circumference. There are an infinite number of great circles of equal length running around the globe, e.g. the circle formed by the Greenwich Meridian and the 180 degrees meridian; the circle formed by the 130 degrees west and 50 degrees east meridians. Of the lines of latitude, only the equator is a great circle.
When drawn on a globe great circles appear as straight lines, but when they are drawn on flat maps of the world they may not appear so. In fact on many maps great circles appear curved and routes along a straight line joining two places. This is an illusion created by the distortion of the shape of the earth to allow it to be drawn on a flat map.
Modern aircrafts follow routes along sections of great circles for speedy long-distance flights and thus cut down flying time. But it is not always possible to follow great circle routes. Firstly, air routes must link numerous cities and thus planes proceed in short 'hops' from place to place; secondly, it may be impossible to fly along great circles for political reasons if some countries forbid the use of their air-space; thirdly, air routes tend to follow the land in case of accidend and rarely fly for long distances over the sea. However, where long distances have to be covered over uninhabited regions, great circle routes are the quickest. They are therefore used in crossing polar regions. Some of the major great circle routes over the pole include that from London to Vancouver or Los Angeles, that from Tokyo to Stockholm and that from Tokyo to Mexico City. Polar routes are not only quicker but also relieve air-traffic congestion on the very crowded conventional routes.

Day and Night (Earth's rotation)

When the earth rotates on its axis, only one portion of the earth's surface comes into the rays of the the sun and experiences daylight. The other portion which is away from the sun's rays will be in darkness. As the earth rotates from west to east, every part of the earth's surface will be brought under the sun at some time or other. A part of the earth's surface that emerges from darkness into the sun's rays experiences sunrise. Later, when it is gradually obscured from the sun's beams it experiences sunset. The sun is, in fact, stationary and it is earth which rotates. The illusion is exactly the same as when we travel in a fast-moving train. The trees and houses around us appear to move and we feel that the train is stationary.

Evidence of the Earth's Sphericity

There are many ways to prove that the earth is spherical. The following are some of them. 1. CIRCUMNAVIGATION OF THE EARTH. The first voyage around the world by Ferdinand Magellan and his crew, from 1519 to 1522, proved beyond doubt that the earth is spherical. No traveller going roumd the world by land or sea has eve encountered an abrupt edge, over which he would fall. Modern air routes and ocean navigation are based on the assumption that the earth is round. 2. THE CIRCULAR HORIZON. The distant horizon viewed from the deck of a ship at sea, or from a cliff on land is always and everywhere circular in shape. This circular horizon widens with increasing altitude and could only be seen on a spherical body. 3. SHIP'S VISIBILITY. When a ship appears over the distant horizon, the top of the mast is seen first before the hull. In the same way, when it leaves habour, its disappearance over the curved surface is equally gradual. If the earth were flat, the entire ship would be seen or obscured all at once. 4. SUNRISE AND SUNSET. The sun rises and sets at different times in different places. As the earth rotates from west to east, places in the east see the sun earlier than those in the west. If the earth were flat, the whole world would have sunrise and sunset at the same time. But we know this is not so. 5. THE LUNAR ECLIPSE. The shadow cast by the earth on the moon during a lunar eclipse is always circular. It takes the outline of an arc of a circle. Only a sphere can cast such a circular shadow. 6. PLANETARY BODIES ARE SPHERICAL. All observations from telescopes reveal that the planetary bodies, the sun, moon, satellites and stars have circular outlines from whichever angle you see them. They are strictly spheres. Earth, by analogy, cannot be the only exception. 7. DRIVING POLES ON LEVEL GROUND ON A CURVED EARTH. Engineers when driving poles of equal length at regular intervals on the ground have found they do not give a perfect horizontal level. The centre pole normally projects slightly above the poles at either end because of the curvature of the earth. Surveyors and field engineers therefore have to make certain corrections for this inevitable curvature, i.e. 12.6 cm to 1 km. 8. SPACE PHOTOGRAPHS. Pictures taken from high altitudes by rockets and satellites show clearly the curved edge of the earth. This is perhaps the most convincing and the most up-to-date proof of the earth's sphericity.