Measuring Time - How do we measure time

Have you ever wondered why there are only 24 hours in a day or why 60 minutes makes one hour or how seconds or minutes are calculated. Basically, what I mean is how do we measure time. How does one decide what constitute a second, minute, hour or a day. Also, ever wondered how ancient people used to measure time. Let's see how are we measuring our time.

All time keeping devices depend on counting a regularly repeated phenomenon. The ancient people used to measure time based on daily, monthly or yearly cycles of the sun or moon. The modern clocks are based on repeated mechanical or electronic oscillations(vibrations). The frequency of vibrations determines the potential accuracy of the clock. The more frequent the vibrations, the greater the potential accuracy of the clock. For example, a quartz watch typically vibrates at 32,768 hertz i.e. 32,768 times a second and hence comparatively keeps better time than a pendulum clock which oscillates only twice a second. As the world becomes a global village, it became imperative for the world to follow one accurate time standard. This is called UCT(Universal Coordinated Time), and is based on the average time signal received from over 200 atomic clocks worldwide.

• Pendulum Clock:

  
  In the 16th century, the Italian scientist Galileo Galilei used the regular swing of a pendulum to measure periods of time. He suggested that a pendulum could be connected to the hands of a clock to turn them in regular steps.

• Nist 7 Atomic Clock:

  
  Nist 7 Atomic Clock was developed by the US National Institute of Standards And Technology, in the early 1990s. At that time, this clock was the most accurate time keeping device in the world, precise to within one billionth of a second per day.

• The Atomic Fountain:

  
  At present, the atomic fountain is the most accurate time keeping device.  It was developed in the early 1990s and is more accurate than a standard atomic clock such as NIST 7.  The fountain measures time with greater accuracy because it uses cooler, slower moving atoms than an atomic clock.  Atomic fountain devices are accurate within one tenth billionth of a second per day.

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