American radio engineer who was employed at the Holmdel Field Station of Bell Labs to maximize the signal-to-noise ratio for the shortwave trans-Atlantic radiotelephone. Using a rotating shortwave receiver array (a Bruce array) operating at 20.5 MHz and 45 KHz, he discovered extraterrestrial radio "noise" in 1932-1933. Jansky noted a continuous interference which changed direction over the course of the day. At first, he believed it was caused by the sun, but then noticed that the time of the peak was shifting in solar time over the course of the year. His suspicion was aroused, however, when a partial solar eclipse of Aug. 31, 1932 did not affect the signal. In December, he realized that his data was consistent with a source moving across the sky with a period of the sidereal day. He published this conclusion in Nature and Proc. Inst. Radio Engineers. His discovery was also emblazoned across the first page of the New York Times on May 5, 1933.

In 1933, Jansky concluded that the emission came from the entire Milky Way galaxy, although it was strongest at 18 hours ( ± 30 minutes) in the direction of the constellation Sagittarius. Unfortunately for radio astronomy, his other tasks left him little time to pursue his discoveries from 1934 onward. His life was cut short by a liver ailment (Bright's disease), which led to high blood pressure. He died of a stroke at the age of 45. His discoveries, however, were pursued by Reber and led to the enormously successful field of radio astronomy.

Reber