If you've seen the Big Blue Chinese Star Chart at the Adler, you understand why we call it that. It is usually in storage, to protect it from light, but has emerged this year to play a role in the Cosmic Wonder celebration. Four feet tall, six feet wide, and colored a deep, rich blue, it is impossible to mistake for anything else in our historical collections. A circle three feet in diameter dominates the image, showing a star field consisting of hundreds of stars. Some of them are in familiar configurations, but many are lined up in orderly formations no one has ever seen in the sky.
Our chart is technically not a print but a rubbing, based on an 800-year-old Chinese stone artifact called the Suchow chart. The dots and lines you see were carved into the stone. A damp sheet of thin paper was then laid across the stone and pressed firmly into its grooves. Finally, blue ink was wiped lightly across the paper, coloring all of it except the portions that had been pressed into the grooves. This laborious early technology enabled the possessor of the stone chart to make multiple copies on paper.
The remarkable thing about the chart as a whole is the way it tries to combine observable aspects of the sky (such as the Pole Star and the Big Dipper) with features that seem to us like utter fancy (numerous circular asterisms, and a few that seem to be drawn up in military formation, as at the top right of the chart). These are surely a clue that the chart was not intended to have a purely astronomical function. Like most artifacts from Chinese antiquity, the Suchow chart asserts that the organization of Chinese society reflects the organization of the world itself, in particular that of the heavenly world. And vice versa: the heavens reflect the structure of society. At the center are the Emperor and the Pole Star.
Perhaps the most intriguing thing about the star field on the chart is the presence of curving lines setting off a region of the sky. The region enters from the top of the chart, loops around to the left of center, and splits into two lobes below and to the right of center. It looks for all the world like an attempt to show the Milky Way!
At the end of the Hundred Days of Cosmic Wonder, we will have to return our Big Blue Chinese Star Chart to a vault, to protect its vibrant blue color from fading in the light. This summer could be your last chance for quite a while to see it!
Written by Bruce Stephenson, curator, Adler Planetarium