Frank D. Drake, an investigator in the SETI (Search for Extra-Terrestrial Intelligence) program, once said that the large radio telescope in Arecibo, Puerto Rico (Figure), "can detect a signal which lays down on the entire surface of the earth a power of only one picowatt."(a) What is the power that would be received by the Arecibo antenna for such a signal? The antenna diameter is 300 m.(b) What would be the power of an isotropic source at the center of our galaxy that could provide such a signal? The galactic center is 2.2 x 104 1 y away. A light-year is the distance light travels in oneyear.