Who first measured the distance from the Earth to the sun?
Historically, the first person to do this measurement was Aristarchus (310-230 BC). He measured the angular separation of the Sun and the Moon when its phase was first or third quarter to derive the distance between Earth and Sun in terms of the distance between the Earth and the Moon. Eratosthenes (276-194 BC) also measured the distance between Earth and Sun as 804,000,000 stadia. The first scientific measurement of the Earth-Sun distance was made by Cassini in 1672 by parallax measurements of Mars (he observed Mars from two places simultaneously). We apply basic trigonometry to measure distance between sun and earth now a days to measure it upto greatest accuracy. You will read it in your college physics course. also see : http://curious.astro.cornell.
