How fortunate we are! If we had lived in the ancient times, we could only have taken a sneak peek at this astronomical instrument.

You may ask, "It's just an instrument, not some secret weapon; why the big fuss if people in ancient times wanted to lay their hands on it? The reason is, studying anything related to the sky in private was strictly prohibited among the general populace in ancient China (you might end up in stockade if you did so!). Ancient Chinese believed that the starry sky was a reflection of the secular world. Different celestial phenomena, including the motion of the Sun, Moon and planets, could be viewed as portents of the rise and fall of regimes. As this instrument was used to measure the positions of celestial bodies, it could, to a certain extent, reveal some divine prophecies including such heavily guarded secrets like the well-being of the supreme ruler. It therefore comes no surprise that the study of astronomy was taboo in ancient China.

Astronomy in ancient China thus followed its own distinct path of development. It began with astrological purposes in mind but serendipitously stimulated the development of observational instruments and the comprehensive documentation of astronomical phenomena. Known as the Armillary Sphere, this instrument is made of three sets of giant rings. The hollow tube in the innermost ring, called the Sighting Tube, is used to point at the target of observation. For example, when we want to observe Mars, we will adjust the Sighting Tube until we can see it through the Tube. The position of the planet can then be read from the graduations on the Armillary Sphere. You may wonder, "Really that simple? Isn't it similar to a child's play of rolling a paper tube to mimic a telescope?

When looking closer at the device, we could also see that there are markings on some of the giant rings. What are these rings for? We will answer these questions in the next episode. Stay tuned.

Let's think
1. What features on the Armillary Sphere show that it is a royal instrument that can only be used by the imperial court?
2. A country has an icon of an Armillary Sphere on its national flag. Which country is it? What is so special about Armillary Spheres in the history of this country?