I am working on a world which is very dark due to an opaque gas layer in the hight atmosphere; but it is opaque mostly in the terahertz range. The creatures in this world therefore rely very little on visible light. Some creatures have evolved sensitivity to radio waves (inspired by a handful of questions here in WB).
This answer to Best place on an humanoid body to develop biological radio? gives an example of a low-power, active radar device for short range that consumes 20 watts of power, which is about 0.86 kcal/hour. This may be prohibitive for smaller creatures (in the 1~5 kg of body mass, I think), so I wonder if passive radar could be used by them.
Could radio emissions from the planet's parent star, and gas giants in the same star system or other radio emission sources be reflected by the environment and perceived by such creatures, akin to how we can see by starlight?
I am not worried about the resolution of this kind of sight. I am more worried about whether radio emissions from space have enough energy to excite my aliens' radio-sensitive organs as much as starlight excites our retinal rods.