It was previously home to Wales's largest optical astronomical telescope. An airborne observatory is an airplane, airship, or balloon with an astronomical telescope. In a refracting astronomical telescope the entrance pupil is identical with the objective. The Steward Observatory uses a Silly-Putty backed lap to grind astronomical telescope mirrors. Gassendi also left him an astronomical telescope he had been left by Galileo. His astronomical telescope is now housed in the rooms of the August Derleth Society.