Mathematics Is Magical (Educational) Poem by Spock the Vegan

The Greek philosopher Eratosthenes of Cyrene
knew that on the summer solstice, June 21, when
the sun was at the zenith in the city of Syene,
Egypt (now Aswan) , that a vertical stick would cast
no shadow. At the same time, a vertical stick in
Alexandria,500 miles north, would cast a shadow
a little over 7 degrees north of the zenith.
He used geometry to calculate the circumference of
the Earth, but we can use a ratio (simple algebra) :
360/7.2 = X/500
X = 360/7.2*500
X = 25,000 miles.