MEASURING EARTH'S CIRCUMFERENCE WITH JUST TWO STICKS.

Today, using satellite technology, we can accurately measure the circumference of earth. But hundreds of years ago, people had measured circumference approximately just using sticks and shadows.

Now, choose a place in the earth at which you get no shadow around noon. (not all places, throughout the year gives zero shadow at noon. You have to do some research to find that proper place and proper date).

CHENNAI OBSERVED ZERO SHADOW DAY ON 24-04-2018.--THE HINDU

At that place, and on that day, you fix a stick A (say one meter long). Ask your friend to fix another stick B of same length at some location which is hundreds of kilometers away. When you get 'null shadow' at some instant, your friend will get some length of stick's shadow due to earth's curvature. (refer figure)

At the time, when the stick A's shadow vanishes, ask your friend to measure stick B's shadow. (of course, through phone).

Now, come to the diagram, complete the triangle pqr, mark the shadow's length and stick's length. We can calculate the angle 'x' using trigonometry. Now extend the sticks' line to the center of the earth. The geometry tells us that the angle made at the center by the two lines is also 'x'. The length of the arc 'ps' held by the angle x can easily be found using google map. (that is, the distance between the sticks A and B).

If the angle x holds the length ps, what is the length held by the angle 360 degrees or 2 pi radian. That can be easily calculated and it is the circumference of earth.

With some mathematics and two sticks, people have calculated the circumference of the planet without circumventing it.

The actual circumference of our planet is 40075 km.

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