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  • Sohini Sarkar

What Time Is It?

Telling time today is a simple task. We have standardised units and ways of calculating time. We also have a set of time zones so that we are all following the same system. We have readily available instruments that tell us what time it is and how much time has passed. Just one quick glance at your phone’s lock screen and you know whether you are late to school or ten minutes early.

Now, imagine a world without clocks. We only have our surroundings to help us gauge what time it is. The position of the sun in the sky should give us a general idea but not an accurate reading. This is what it was like a few centuries ago before the invention of clocks. This changed with the brilliant invention of sundials. The first known sundial still preserved is an Egyptian shadow clock from at least the 8th century BCE. There is only one glaring disadvantage to using a sundial and that is the fact that it cannot be used after the sunset.

The sundial is made of two basic parts: the gnomon and the dial. The dial is usually a flat plate with numbers on it indicating the hours. The dial plate may also be a part of a sphere, cylinder, cone, helix and other shapes. The gnomon or style is a thin stick or rod which casts a shadow on the dial telling us which hour of the day it is. If this is what a sundial is, why can we not use a simple stick in the ground? The reason a simple stick would not suffice is that the sun’s visible movement changes daily due to the tilt of the earth’s axis. There are ways a sundial overrides this problem. The first method is to keep the base platform, on which the sundial rests, aligned with the latitude of that particular place and the gnomon perpendicular. Another method is to keep the base steady and move the gnomon to reflect the changes due to the earth’s axis.

The biggest sundial in the world is located in Jaipur, India. It is in one of the five Jantar Mantars in India. This Jantar Mantar was made in 1734 by Sawai Jai Singh II and is an astronomical observatory. Today, it is a tourist attraction but back then it was one of the only ways of telling time.

The Jantar Mantar in Jaipur, Rajasthan which houses the largest sundial in the world

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