Astronomy
The Principles Behind Radio Telescopes and Interferometry
Quick fact
The Event Horizon Telescope, an Earth-sized interferometer of radio telescopes, captured the first image of a black hole's shadow despite the black hole being about 55 million light-years away.
Why this is interesting
You can't see a radio wave with your eyes, yet there is an entire universe glowing at radio wavelengths. How do astronomers turn these invisible signals into detailed images?