Astronomy

The History of Telling Time



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You’ve only got five minutes? No problem, sit your butt down and read this article. Have you ever stopped to wonder what life would be like without your watch, or blackberry, on hand? How did we develop the time scheme that we follow, anyway? And why, after every four years, do we have to add a day in February? Of course you didn’t, you don’t have time for that. But if you did, you’d learn a lot about the history of Sundials.

But, since you don’t have time to do that research, I’ve done it for you. Read on…

The idea of measuring time in 24 hours/day was not developed overnight. It took quite a bit of experimentation. The Egyptians, for example, divided Day and Night separately. The day, they said, had 10 hours, and the night, 12. The reason for this is because their means of time-measurement was the sundial, and of course, the sun wasn’t casting a shadow at night. While the Egyptians might have been a little off in their calculations, overall they had the right idea. Building on their work, the Greeks and Romans were able to more accurately define time. With the development in mechanics, pendulum clocks were made, and then on a smaller scale, we created watches. With a boom in technology, the development of digital clocks and satellites abolished the need for sundials to check the accuracy of our time-pieces. Humanity’s obsession with time has a long history, and at all began with the sundial. You might take a moment the next time you glance at your watch to appreciate just how far we’ve come.

The first sundial, was really just a stick in the ground, called a gnomon. Mesopotamians eventually realized that the shadow cast by a stick changed in position and length as the sun “moves” around it. This was not just the first device for telling time, but also the first scientific instrument. 

This simple stick in the ground slowly developed into the sundials we know today that decorate our gardens. Between 2500-2000 BCE, the Egyptians built round obelisks to place underneath the gnomon. Eventually, they started marking on these obelisks to give a more precise idea of time each day. Circa 300 BCE, the Greeks and Romans built more complex sundials, using their knowledge of geometry. They discovered that a slanting object’s (because it is parallel to the earth’s axis) shadow did not move depending on the season, and it was therefore more accurate. With trigonometry, the Greeks were able to plot out the hour lines.


Sundials were so effective that it is not until 1300 AD (thus, about 5-6 thousand years after the sundial was discovered) that the first mechanical clock was invented. Moreover, until the 19th century, since mechanical clocks tend to lose time, sundials were still used to check the accuracy of mechanical clocks.

To answer the questions in the opening paragraph:

- The reason we follow a 24 hour time scheme is simply based on the rotation around the sun.

-The reason we add a day in February every four years, is because my first statement—that the Earth does a complete turn in relation to the sun every 24 hours is actually false. It is really every 24 hours and a little bit. This means that the Earth makes one full trip around the sun every 365.25 days. Rather than complicating matters by making one day 24 hours plus a little bit-we simply tack on a day in February every 4 years.

And the reason we are able to tell time at all?

Because of the sundial.

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More about this author: Rebecca O'Brien

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ARTICLE SOURCES AND CITATIONS
  • InfoBoxCallToAction ActionArrowhttp://www.abc.net.au/science/articles/2011/11/15/3364432.htm
  • InfoBoxCallToAction ActionArrowhttp://www.accuratesundials.com/site/591582/page/143772
  • InfoBoxCallToAction ActionArrowhttp://www.accuratesundials.com/site/591582/page/143772