The Voyager 1 spacecraft is over 11 billion miles away, but it's emitting an extremely faint radio signal that can be detected here on Earth. Recently, astronomers used this signal to create a "photograph" of the now-interstellar probe.
To create this image, astronomers used the National Science Foundation's Very Long Baseline Array (VLBA) and Green Bank Telescope (GBT). These instruments are so sensitive that they can pick up Voyager's feeble 22 watt signal (the equivalent of a car-mounted police radio, or in terms of visible light, a refrigerator bulb).
Needless to say, the challenge was not so much in picking up the signal as it was in pinpointing Voyager's precise location in the sky. To do it, the astronomers used both instruments to plot Voyager on a celestial grid system in a technique that's akin to establishing markers on a highway. This allowed them to nail the spacecraft's position to within fractions of an arc-second of where it was predicted to be (an arc-second being roughly the size of a penny viewed from about 2.5 miles away).
[Via LA Times]