The celestial globe invented by zhang heng , chinese scientist of the east han dynasty ( 25 a.d . - 220 a.d. ) , was the first of its kind in the world. it determined that the angular diameter of both the sun and the moon was 0.5 . 中国东汉科学家张衡发明的天球仪是世界上最早的天球仪。
Angular diameter of the retro - reflecting device 回复反射装置的角直径
百科解释
The angular diameter or apparent size of an object as seen from a given position is the “visual diameter” of the object measured as an angle. In the vision sciences it is called the visual angle.