TIME AND LONGITUDE

TIME
To avoid confusion and make the study of time relations simple, it is necessary to think of the earth as stationary and of the sun as completing one circuit about the earth every 24 hours.

TIME AND LONGITUDE Time and longitude are re­lated. As the earth rotates, every place experiences the phenomena of sunrise, noon and sunset. It is noop when the sun is at its highest position in the sky. This position of the sun is called zenith. (At noon, shadows are at their shortest.)

One hour of time is equivalent to 15° of longitude. This can be calculated and understood from the fact that the earth completes one rotation on its axis in 24 hours, so in eaeh hour, it covers 15° of longitude to cover 360° of longitude in total. This also means that 1° of longitude is covered every 4 minutes during the daily rotation of the earth. This equality forms the basis of all calculations concerning time belts of the globe.

LOCAL TIME AND STANDARD TIME Local time is the time of the day at a place as indicated by the position of the sun, Le., it is the mean solar time based on thE; local meridian. All the places located on the same meridian, regardless of how far they are from each other, have the same local time. Places located on different meridians have, unlike local times, times differing by four minutes for every degree of longitude. If, however, each place had its local time, there would be chaos-we would have to spend our time adjusting clocks and watches. So, we have the standard time, which is the mean time of a particular meridian (generally a central one), adopted as a system of time for the entire country, and all clocks within this belt are set to a single time. Each time-zone or country differs from Greenwich Mean Time in whole or half-hour units.

The general understanding among the countries of the world is that the standard meridian selected for an areal country is in multiples of 7.50 longitude. Every 7.50 of longitude makes a difference of 30 minutes or half-an-hour. This enables simple calculation of time differences.
As the earth rotates from west to east, places
east see the sun first. Therefore, (i) For each 10 of Ion towards the east, a time of four minutes has to be , (ii) For each 10 of longitude towards the west, a ti four minutes has to be subtracted.

Most countries adopted a standard time followi International Meridian Conference of 1884, held in ington.


TIME ZONES A time zone is an area in the recording the same time. As it takes the earth 24 to make one rotation, Standard Fleming, a Can suggested dividing the earth into 24 time zones. Time of the world are described in terms of the differeJ number of hours between the standard meridian (] zone and the Greenwich meridian. In order to distir the direction of these zones, the time for all places east of Greenwich is designated fast, and time for all place~ of Greenwich is designated slow.

The Greenwich meridian at 0° longitude passes through Greenland Sea and N gian Sea, and the countries of the United Kingdom, F. Spain, Algeria, Mali, Burkina Faso and Ghana, and through the South Atlantic Ocean. In some countries a large West-East extent, more than one time zone be necessary, e.g., the USA and Canada both have fiVE zones; Australia has three; Russia has eleven.