Abstract: In an astronomical telescope assembly which can be used in a non-observatory type building, a refracting telescope is mounted for rotation about its optical axis with the optical axis parallel to the axis of earth's rotation and with the eyepiece end of the telescope higher than the objective end, which extends to the outside of the building through an opening in a wall of the building. A reflector unit carried by the objective end of the telescope has a reflecting surface which is pivotable about an axis perpendicular to the optical axis for directing light into the telescope, the reflecting surface being manually positionable about its axis by control means provided at the eyepiece end of the telescope. The telescope proper may be of known construction or may employ spars upon which various optical elements can be releasably mounted for forming different optical systems. Automatic solar tracking apparatus is provided.