A sunrise or sunset seen from home is enough to confirm that the Earth is round. Indeed, when the bottom of the clouds is lit (when there are clouds of course), it proves that the light comes from “below” clouds. And so … that the Earth is round!
Rotundity of the Earth in sketches
In the evening, just watch a sunset with some clouds (not a sky completely covered, just a few clouds!). We sometimes see that the sky is quite gray then lights up a little more for a few minutes: the bottom of the clouds is lit.
Similarly at dawn, it happens that a cloudy sky lights up pink and orange for a few minutes then becomes grayer. The clouds are lit from below before the sun “rises” into the sky.
Illustration of the sunset: rotundity of the Earth
If the Earth was not round – that is, flat! – the sun could never light the clouds from below. At sunset, the rays of light would be horizontal; not producing the beautiful effect of clouds lit from below.
Sunsets or sunrises
A rather ordinary sunset can illustrate the rotundity of the Earth. Here, for example, a summer evening in Bas-Rhin:
Sunset: view to the west
Sunset: view to the east
A few minutes later, the bottom of the clouds lights up:
Clouds lit from below: Earth is round
If the sky is perfectly pure, no cloud can prove the rotundity of the Earth:
Sunrise “missed”: here on a Vosges summit, no proof that our Earth is round
With cirrhus (high altitude clouds), the effect will be the same, a little earlier before sunrise or a little later after sunset:
Aurore on the Alps: clouds lit by the bottom
Poets have largely been inspired by these radiant beauties of nature:
“The horizon with copper vapors where man lives” (Charles Marie Leconte de Lisle)
“These few signs that laze in the summer skies or those evening promises that make our reason for living” (Albert Camus)
“Will you be told in the evening back, intense, gigantic, feverish?” (Alexander Taesch)
Conclusion on the rotundity of the Earth
From its window or terrace, thanks to sunrises and sunsets, we can see that the Earth is round