Gnomon

The name of an ancient astronomical instrument. Also known as "shadow symbol".

When Guo Shoujing developed the high table to measure shadows, the shadow of the crossbeam projected onto the gnomon was not very clear, which inevitably affected the accuracy of the measurement. To ensure accurate observations, Guo Shoujing created the "Gnomon".

"The system of the Gnomon is made of a copper sheet, two inches wide, and twice as long as it is wide, with a hole in the middle, like a needle, and a smooth square as a base, one end of which is set up as a pivot, so that it can be opened and closed, and one end of which is bent so that it is tilted, the north end being high and the south end being low, and it is moved back and forth to adjust it within the virtual beam. The hole is exposed to sunlight, only as big as a grain of rice, and the crossbeam is dimly visible in it." - History of Yuan Dynasty, Astronomical Records

The Gnomon uses the principle of pinhole imaging to make the virtual shadow cast by the crossbeam of the high table a precise and clear image that is projected onto the gnomon, achieving the highest accuracy in human history of shadow measurement.

The model requires two m3*16 screws to secure the rotating axis.