Hello guys! Hope all is well.
I just read today that the voyager space craft has reached interstellar space. While reading about the article in wikipedia i found a picture with the caption "Image of Voyager 1's radio signal on February 21, 2013" ........What on earth is an "image of a radio signal"??? Can someone please explain it to me? i do know what a radio image of a galaxy would be, for example; but cant comprehend what an image of a radio signal is. Thank You.

 

The image of a radio signal is made with a radio telescope. It shows RF intensity on a particular frequency as a function of celestial coordinates (declination and right ascension for example). Notice the absence of any other RF sources in the vicinity of Voyager. It uses a false color mapping to show different levels of intensity.