WORLD CIVILIZATION

Detailed explanation-1: -Aristarchus’s contribution to astronomy was the theory of heliocentric planetary system, and Eratosthenes’s was the conclusion that Earth has a round shape.

Detailed explanation-2: -Eratosthenes was also the first to calculate the tilt of the Earth’s axis, which he figured with remarkable accuracy; the finding was reported by Ptolemy (85-165 CE). Eratosthenes also calculated the distance from the Earth to the Moon and to the Sun, but with less accuracy. He made a catalog of 675 stars.

Detailed explanation-3: -Aristarchus was a Greek astronomer who lived at the same time as Eratosthenes and first proposed the idea that the Earth orbited the Sun. He then measured the width of both Sun and Moon and determined they were 2° of arc in width.

Detailed explanation-4: -By measuring the length of the shadow in Alexandria at noon on the Summer Solstice when there was no shadow in Syene, he could measure the circumference of the Earth!