Saturday, May 5, 2012

A 2nd Century BCE Chinese Gnomon?

For general information on what a "gnomon" is, please see Wikipedia.   Of note is this entry:

The Chinese also used the gnomon, mentioned in the 2nd century Nine Chapters on the Mathematical Art as being used much earlier by the Duke of Zhou (11th century BC).

See Sundial History for further information and a time line about the development of the use of the gnomon and the invention of the sundial that it led to, after many centuries. 


May 3, 2012
Oldest Astronomical Instrument Discovered in China
Chinese scientists have proposed that an object collected 35 years ago from a tomb of the Western Han Dynasty in Fuyang city and called “lacquerware of unknown names” could be a gnomon with template.

An artist's rendtion of what the object from the tomb of Xiahou Zao may look like.
In 1977, archaeologists unearthed a great number of precious relics, including the unknown object, in the tomb of Xiahou Zao (the 2nd century BCE), the 2nd Marquis of Ruyin of the Western Han dynasty. However, no one has been able to identify the object as well as to explain the possible function of a pair of overlapping lacquered disks found in the same tomb.

A team of Yunli Shi, a professor at the Department of the History of Science and Scientific Archaeology, University of Science and Technology of China, has now proposed that the object is a special gnomon with template, while a pair of lacquered disks is an equatorial device for the positional observation of celestial bodies. Both are the oldest astronomical measuring instruments with definite information of date that can still be seen in the world. The findings appear in the Studies in the History of Natural Sciences.

The scientists noted that the gnomon with template is a typical instrument used by ancient Chinese astronomers in determining the advent of different seasons with the gnomon shadows cast on the template by the midday Sun.

The gnomon from the tomb of Xiahou Zao has two symmetric and foldable parts. As being fully set up in the south-north direction, the midday Sun will cast the shadow of a vertical tablet in the northern half onto three fixed positions on the template respectively on the days of the Summer Solstice, the Vernal/Autumnal Equinoxes, and the Winter Solstice.

“Geographically, this type of gnomon with template can only be used on the given latitude, and the one from the tomb of Xiahou Zao fits just right with the region between the capital of the dynasty Chang’an and the fief of the Marquis of Ruyin Fuyang,” explained Prof. Shi.

The edges of the two overlapping disks are marked respectively with the complete degrees of a celestial circle, and the names and degrees of each of the 28 lunar lodges.

Previous studies have suggested that they may make either an astrological tool similar to the two cosmic disks for divination from the same tomb, or a kind of astronomical instrument, but both theories are in need of definite evidence.

Mounted on top of a lacquerware box, the disks form a complete device good for the equatorial observation fitting just right with the geographical latitude of Fuyang, a prefecture-level city in northwestern Anhui province, China.

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