TIME

THE STORY OF TIME  -Part 1

The Universe in a year 

The American astronomer Carl Sagan first suggested a cosmic calender as a way of helping people understand the history of Universe.He put everything into the scale of a calender year:the galaxies are formed over nine months and the earth appears in September.

               "Human history is crowded into the last five minutes of the year.Recent time is divided into seconds and fractions of a second.So everything that happened in the last 475 years.take place in less than the last second of the last minute of the year."

•  Earth's life in a year

  • 1st January (midnight) : Big Bang - Universe Forms
  • 15 March : First stars and galaxies form
  • 1 May : Milky Way galaxy forms
  • 8 Sep   : Sun forms 
  • 9 Sep   : Solar System forms
  • 12 Sep : Earth forms
  • 13 Sep : Moon forms
  • 20 Sep : Earth's atmosphere forms
  • 1 Oct   : Earliest known life on Earth
  • 7 Oct   : Earliest Known Fossil
  • 18 Dec : First Many-celled life forms
  • 19 Dec : First Fish
  • 21 Dec : First land plant; First insects
  • 23 Dec : First reptiles
  • 24 Dec : First dinosaurs
  • 26 Dec : First mammals
  • 27 Dec : First birds
  • 28 Dec : First flowering plants
  • 28 Dec : Dinosaurs extinct
  • 31 Dec : Homo sapiens 
   

Time Zones 

World time zones and the International Date Line

The Earth is constantly turning on its axis.If people everywhere set there clock to the same time,midnight would be in the middle of the night on one side of the globe , but the middle of the day on the opposite side.To avoid this problem the Earth is divided into artificial time zones.These generally follow lines of longitude-imaginary lines running from the North to South Pole.Some large countries,such as the USA, cover several time zones.Mainland USA is divided into Atlantic,Eastern,Central,Mountain,Pacific and Alaska zones,with Hawaii and other islands falling into further zones.                                              

Since the Greenwich Prime Meridian (0 degree) was established in 1884,there have been 24 time zones,each of 15 degree longitude and an hour apart.Those to the east are ahead of Greenwich by one hour per zone.Those to the west are behind by one hour each.Some countries,such as India,have chosen zones halfway between those on either side,so that the whole country can use the same time.   

The International Date Line

The International Date Line is a imaginary line between the North and South Poles.It marks the end of one day and the start of another.Countries to the East of the Date Line are always a day ahead of those to the west.Travelers who cross the line gain or lose a day,depending on which direction they are going.

Most of the Date Line follows 180 degree Meridian (on the opposite side of the globe from 0 degree,the Greenwich Meridian). The line generally passes through sea,but where it would pass through or near certain land areas, it is adjusted it.It zigzags around islands, putting them either into the west or the east, and avoids dividing Siberia in north-east Asia into two time zones.