Most of the observatory's large bronze astronomical instruments -- mystifying combinations of hoops, slides, and rulers stylishly embellished with dragons and clouds -- were built by the Jesuits in the 17th and 18th centuries. You can play with reproductions of the Chinese-designed instruments they superseded (the originals were moved to Nanjing in 1933 and, for unexplained reasons, haven't been returned) in the grassy courtyard below. At the back of the garden, there's a "we-invented-it-first" display outlining the achievements of Song dynasty astronomer Guo Shoujing, who also has his own memorial hall on the northern tip of Xi Hai. To the right of the entrance there's a more useful exhibition, which houses a photo of a bone from 1300 B.C. on which China's first astronomers etched a record of solar eclipses, details of which are still used in present-day astronomy.

Copyright: Excerpted from Frommer's Beijing, 5th Edition, (c) 2008, Wiley Publishing, Inc.

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