A sundial measures the movement of the sun across the sky each day .
日晷测量每天太阳跨过天空的运动。
Yet , to the north at alexandria , a sundial cast a shadow even at the solstice midday , because the sun was not directly overhead there .
而在北边的亚历山大城，日晷会投下一个影子，因为在正午太阳并不在头顶正上方。
Eratosthenes knew that at noon on the day of the summer solstice , the sun was observed to be directly overhead at syene ( modern-day aswan ) : you could see it from the bottom of a deep well , and a sundial cast no shadow .
Forbidden cit beijing china chinese travel tiananmen qing dynasty history eight nation alliance empire empress ming museum palace dowager cixi ballustrades ancient sundial .
