Suzhou (= Soochow) planisphere
A more complete representation of the Chinese sky than the Dunhuang manuscript
is provided by this circular chart from Suzhou, formerly known in the west as
Soochow. This chart was engraved on stone in 1247 but is a copy of an earlier
drawing from around 1193. Reproductions of the engraving are taken from an
ink-on-paper rubbing, like a brass rubbing; as a result, the stars and lines
appear white on a black background. This type of circular chart is usually
termed a planisphere.
The Suzhou planisphere depicts the sky from the north celestial pole to about 55° south, indicating that the observations were made from a latitude of about 35° north. Radiating lines, like irregular spokes, demarcate the 28 xiu. These lines extend from the southern horizon (the rim of the chart) to a
circle roughly 35° from the north celestial pole; within this circle lie the circumpolar
constellations, i.e. those that never set as seen from the latitude of
observation. The familiar figure of the Plough can be made out near the lower
left of this inner ring, but apart from that there are few similarities between
the Chinese star patterns and western ones.
Two intersecting circles represent the celestial equator and ecliptic, which the
Chinese called the Red Road and the Yellow Road respectively. An irregular band
running across the chart outlines the Milky Way, called the River of Heaven – even the dividing rift through Cygnus can be made out. All 1464 stars from Chen
Zhuo’s catalogue are supposedly included (an inscription on the planisphere tallies
the total as 1565, but this is clearly an ancient Chinese typographical error);
not all of the stars show up on the rubbing, however.
The Suzhou planisphere
The Suzhou planisphere is a circular representation of the sky centred on the
north celestial pole. It was engraved on stone in 1247 and is a near-complete
representation of the stars and constellations recognized in China at that time
and for some centuries before. An indicator of this map’s antiquity is that the north celestial pole lies over 5° from our present-day pole star, Polaris, because of the effect of precession.
When the star positions for the Suzhou chart were observed, in the 11th century
AD, the north celestial pole lay in a barren area of sky in the modern
constellation Camelopardalis. At that time the closest naked-eye star to the
pole was the 5th-magnitude double star we know as Struve 1694 or HR 4893 but
termed the Pivot Star by the Chinese; this star was actually at its closest to the pole early in the
9th century AD.
© Ian Ridpath. All rights reserved