In their attempts to cover all the topics in the given curriculum, teachers often focus more on outlining results and theorems; as opposed to taking us on a journey to discover how the science was derived through pristine ideas, experiments and often-elegant mathematics. One problem this leads to is that we end up knowing several facts and formulas without remembering how they were discovered or why they hold true.
Knowledge that has existed for several years is especially susceptible to being taken for granted. One such example is the knowledge that the Earth is spherical as opposed to flat. In this article, the word ‘spherical’ is used lightly; the exact shape of the Earth is an oblate spheroid, a type of ellipsoid.
Our size relative to the Earth is too small to notice a curve. To a tiny creature that has just learned to walk around a small area of the Earth, there would be no immediate indication that the Earth is round. However, our ancestors gradually collected evidence that contradicted the primitive notion that the Earth is flat. This article is a journey through all the ideas and observations that suggest that the Earth is spherical.
1. Ships and the horizon
The horizon is the line at which the Earth’s surface and the sky appear to meet. When ships sailing away disappear into the horizon, they do so bottom-first. The top vanishes later, which creates the illusion that the ship is sinking. Similarly, when ships appear from the horizon, the top appears first, and then the rest of the ship.
2. We cannot see very far away
Let’s say that you are standing on the West coast of North America on a clear day. While you are able to see the sun and moon in the sky, which are quite far away, you cannot see Japan if you look to the west. The reason you cannot see that far away on Earth is that light travels in a straight line and hence cannot follow Earth’s curve.

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11. Gravity
If the Earth were a flat plane, its center of mass would be the center of the plane and the force of gravity will pull anything on the surface in that direction. This means that if you stand near the edge of the plane, gravity will be pulling you sideways toward the middle of the plane.
12. Variations in the Earth’s gravitational field
Earth’s gravity is slightly weaker at the equator than at the poles. There are two reasons for this. First, since a point at the equator spins faster than a point at a pole, the outward centripetal force at latitudes near the equator is greater and counteracts the Earth’s gravity more. The second reason is that the Earth’s equatorial bulge (itself also caused by the centripetal force) causes objects at the equator to be farther away from the Earth’s center than objects at the pole, and the gravitational pull between two objects is inversely proportional to the square of the distance between them.
The variations in Earth’s gravitational attraction can be measured and provide concrete evidence of the Earth’s shape.
13. The Earth’s shadow
During a lunar eclipse, the sun, Earth, and the moon are aligned such that the Earth’s shadow falls onto the moon. The Earth’s shadow has been observed to be curved as the planet is.

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