Global Geological And Climatic Events

What is Daylight Saving Time (DST)?


From UPSC perspective, the following things are important :

Prelims level: Daylight Saving Time (DST), Equinoxes

Mains level: Not Much

The United States Senate unanimously passed a law making daylight saving time (DST) permanent, scrapping the biannual practice of putting clocks forward and back coinciding with the arrival and departure of winter.

What does this imply?

  • With clocks in the US going back an hour, the time difference between New York and India will increase from the current nine and a half hours to ten and a half hours.
  • In the Southern Hemisphere, the opposite has happened, where countries have “sprung forward”, and time difference with India has reduced.

What is DST?

  • DST is the practise of resetting clocks ahead by an hour in spring, and behind by an hour in autumn (or fall).
  • During these months, countries that follow this system get an extra hour of daylight in the evening.
  • Because the spring to fall cycle is opposite in the Northern and Southern Hemispheres, DST lasts from March to October/November in Europe and the US, and from September/October to April in New Zealand and Australia.
  • Dates for this switch, which happens twice a year (in the spring and autumn) are decided beforehand.
  • By law, the 28 member states of the EU switch together — moving forward on the last Sunday of March and falling back on the last Sunday in October.
  • In the US, clocks go back on the first Sunday of November.

Now try this PYQ:

Q.On 21st June, the Sun

(a) Does not set below the horizon at the Arctic Circle

(b) Does not set below the horizon at Antarctic Circle

(c) Shines vertically overhead at noon on the Equator

(d) Shines vertically overhead at the Tropic of Capricorn

How many countries use DST?

  • DST is in practice in some 70 countries, including those in the European Union.
  • India does not follow DST; since countries near the Equator do not experience high variations in daytime hours between seasons.
  • There is, however, a separate debate around the logic of sticking with an only one-time zone in a country as large as India.

What does this system mean to achieve?

  • The key argument is that DST is meant to save energy.
  • The rationale behind setting clocks ahead of standard time, usually by 1 hour during springtime, is to ensure that the clocks show a later sunrise and later sunset — in effect a longer evening daytime.
  • Individuals will wake an hour earlier than usual, complete their daily work routines an hour earlier, and have an extra hour of daylight at the end.

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