Why is the sky dark at night? Geometric considerations with a historical and pedagogical look at the Olbers paradox

We present the Olbers paradox and some proposals for its solutions with geometric arguments based on simple cosmological and astrophysical models. A little-known sky splendor calculation shows that the Universe expansion to the night darkness is responsible for little more than half of the effect; the remainder comes from the low distribution of stars (and galaxies) that shine during a finite time in the Universe. High school or undergraduate teachers can explore this subject in an instigating, interdisciplinary, and historical way.