It's a device to find out and highlight the visible portion of sky, it consists of a mobile disc (1) that has got a representative map of stars of a celestial hemisphere, a fixed disc (2) overlapped to the map with a window (3) modelled to circumscribe a portion of correspondent shape and dimension to the portion of sky normally visible. A half temporised engine (8) is prearranged to make the fixed disc and the mobile one rotate of complete turn in 24 hours -4' so that the window (3) could permanently find out the portion of sky (4) currently visible. The fixed disc and the mobile disc can be entered according to the period of the year.