What -- exactly -- is an "armillary"?  

We had to look it up, too, so allow us to share what we learned! 

Armillary means: a model of the celestial globe constructed from rings and hoops representing the equator, the tropics, and other celestial circles, and able to revolve on its axis.

As a sundial, the gnomon is the pointed arrow, which casts a shadow showing the time.  This ancient tool was used for centuries in astronomy and science and is still useful, if antiquated. 

Today, the primary use of these intriguing pieces in gardens or yards.  

This item is cast iron and cannot be shipped; it must be picked up at the Montgomery Zoo.