Consider a civilization broadcasting a signal with a power of 1.5×104 watts. The Arecibo radio telescope, which is about 300 meters in diameter, could detect this signal if it is coming from as far away as 122 light-years. Suppose instead that the signal is being broadcast from the other side of the Milky Way Galaxy, about 70000 light-years away. How large a radio telescope would we need to detect this signal?