What did Dengfeng Observatory / Giant Gnomon look like?

A tall platform structure (~12m high) with a horizontal beam (the gnomon) at the top and a stone gnomon (horizontal scale ~30m long) on the ground.

How did Dengfeng Observatory / Giant Gnomon work?

Sunlight strikes the horizontal beam → shadow cast onto the ground-level stone gnomon → the beam's shadow passes through the jingfu pinhole → forms a sharp solar image on the gnomon surface → the position of the solar image at noon is measured → precisely determines the tropical year.

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Dengfeng Observatory / Giant Gnomon

A giant gnomon: a 40-chi-tall gnomon paired with a pinhole imaging device (jingfu) to eliminate shadow-edge blur. Achieved a tropical year measurement accuracy of 365.2425 days.

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Scientific Principle

Pinhole imaging: the small aperture eliminates penumbral blur. The tall gnomon + long gnomon scale magnify the solar shadow displacement, improving angular resolution.

登封观星台

Dengfeng Observatory / Giant Gnomon

Scientific Principle

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