[petuniasevan]

It is indeed an astrolabe.

It is necessary to understand the movements of celestial objects such as the sun and moon in order to make a calendar to determine the passage of time. The astrolabe is a tool for measuring the position of celestial objects and it was also used as a teaching device to explain the movement of celestial bodies. The earth is placed in the middle of the astrolabe, and around it are attached spheres which represent the equators and ellipses of the heavens, and the moon's orbit.

[petuniasevan]

Looks like your astrolabe is a simple one, used only to plot the apparent movement of the sun or moon.