What is in this image? Describe it as if you were explaining it to someone from the 15th century.

This image depicts a fantastical craft, much akin to the ships which sail the oceans but constructed to voyage through the heavens themselves. Imagine a ship crafted of metal and other unknown materials, designed not for water but to soar amid the clouds and stars. Its shape is elongated and pointed at the fore and aft, much like the sharp bow of a sea vessel. The rear explodes with a soft plume, reminiscent of smoke from a blacksmith''s forge, propelling it forward through the air. It bears circles upon its body, perhaps windows, or shields of some sort, through which the mysteries of the heavens can be observed. This wondrous object is akin to what the alchemists and dreamers of your time might conceive as they ponder the possibilities of the ether and the celestial realm.