What he did was simple geometry, and in a way he was the right man in the right place. He heard that the sun was in zenith during the summer solstice ina certai

What he did was simple geometry, and in a way he was the right man in the right place. He heard that the sun was in zenith during the summer solstice ina certain town. He had a good runner measure the distance between Alexandria and that town and then measured the angle of the sun during the solistice in Alexandria (for simplicity, say it was 6 degrees). To get the full circle, just multiple by 60. 6th graders maths.