A sundial measures apparent solar time, usually by measuring the position of the shadow of the sun as it changes through the day. A set of markings are made on the surface on which the shadow is cast, allowing the user to read the time.-wikipedia.en 影を利用して真太陽時刻を計測する装置。紀元前3000年、古代エジプトで使われていたが、起源はさらにその前の古代バビロニアにさかのぼると考えられる。-wikipedia.jp |