The various proofs to show that the earth is spherical in shape are as follows:
1. Sunrise and sunset
If the earth were flat, the whole world would have sunrise and sunset at the same time. Because the earth is spherical and rotates from west to east, the sun rises and sets at different times in different places.
2. Ship visibility
When a ship approaches from a distant horizon, a viewer first sees its smoke, then the mast, and then the whole body of the ship as it nears the harbour. If the earth were flat, the whole ship would be seen at the same time.
3. Circumnavigation of the earth
Ferdinand Magellan’s expedition sailed round the world between 1519 and 1522. The ships kept sailing in one direction and returned to their starting point without reaching any edge, which proves the earth is spherical.
4. The circular horizon
The earth’s horizon appears curved when viewed from a ship or a high cliff. This proves that the earth is spherical, since the circular horizon widens with increasing altitude and can only be seen on a spherical body.
5. Lunar eclipse
The shadow cast by the earth on the moon during a lunar eclipse is always circular. It takes the outline of an arc of a circle, and only a sphere can cast such a circular shadow.
6. Planetary bodies
Telescopes show that the sun, the moon and the planets all have circular outlines from whichever angle they are viewed, so the earth, also a heavenly body, is spherical too.
7. Driving poles on level ground on a curved earth
When poles of equal length are driven into level ground at regular intervals, their tops do not form a perfect horizontal line. The centre pole projects slightly above the poles at either end because of the curvature of the earth. If the earth were flat, the tops of the poles would be level when viewed from either end.
8. Aerial proof
Photographs taken from high altitudes by rockets, satellites and spacecraft show clearly the curved edge of the earth. This is the most convincing and up-to-date proof of the earth’s spherical shape.
How WAEC asks it: “With the aid of suitable diagrams, describe the following proofs supporting the spherical shape of the earth: circumnavigation; Bedford Level experiment; Ship visibility” (WASSCE Aug./Sept. 2018, Geography Paper 3, Question 5).
Examiner’s note: Candidates who scored well backed each proof with a good diagram as well as an explanation.