Karl Jansky

Karl Guthe Jansky was an American radio engineer and physicist who inadvertently opened a revolutionary new window on the universe, creating the science of radio astronomy. Employed by Bell Telephone Laboratories in Holmdel, New Jersey, Jansky was tasked with investigating sources of static interference that might disrupt transatlantic commercial radiotelephone transmissions.

To study this, he constructed a massive 100-foot-long rotating directional antenna mounted on Model T Ford wheels, affectionately known as 'Jansky's Merry-Go-Round'. By 1932, after ruling out local thunderstorms, Jansky detected a steady, faint hiss whose signal peaked once every 23 hours and 56 minutes—a sidereal day. He realized the radio noise was not of terrestrial or solar origin, but was emanating from the heart of the Milky Way in the constellation Sagittarius. Although Bell Labs reassigned him before he could pursue astrophysics, Jansky's discovery spawned radio astronomy. The fundamental unit of radio flux density, the jansky (Jy), commemorates his triumph.