Sun, as a gravitational lens for focusing interstellar signals
The Sun, as a gravitational lens for focusing interstellar signals, is a possibility suggested, in 1979, by Von R. Eschelman of Stanford University, California.1 Since the Sun can act as a gravitational lens, why not use it, asked Eschelman, in the search for messages arriving in our direction from other stars? His calculations showed that the focusing produced by the Sun would yield signals easily detectable by existing interplanetary probes such as Voyager and Pioneer. Yet a formidable problem would remain: the nearest appropriate focal point is 550 times as far from the Sun as the Earth is, and the area in which the detectable signal would be focused would be at most a few km across. Commenting on this, Eschelman said that although it might prove an insurmountable technological difficulty to us at present, radar and microwave communications signals leaking out from the Earth could be picked up by a race slightly more advanced than us using its own stellar gravitational lens.
1. Eschelman, V. R. "Gravitational Lens of the Sun: Its Potential for Observations and Communications over Interstellar Distances," Science, 205, 1133 (1979).