Astrolabes are instruments used for celestial navigation or astronomical observations. There are several synonyms for astrolabes, including celestial spheres, armillary spheres, and planispheres. Celestial spheres are imaginary spheres with the Earth as the center, used to represent the positions and movements of celestial bodies. Armillary spheres, on the other hand, are physical devices consisting of rings and spheres that represent celestial bodies. Planispheres are circular charts that display the positions of stars and constellations in the night sky. These synonyms all have a common theme of relating to celestial bodies, and they have been used across different cultures and time periods to guide travelers, astronomers, and astrologers.