During a solar eclipse #OTD in 1932, Karl Jansky saw no change in the intensity of the faint radio hiss he'd been monitoring. This meant that the sun wasn’t the source. He soon attributed what he called "star noise" to large clouds of ionized gas near the center of the Milky Way.

Scientists didn’t show much interest at the time. Even Jansky didn't really appreciate that he had invented the field of Radio Astronomy #OTD in 1932.
Image: Bell Telephone Laboratories

Jansky was working for Bell Labs at the time, trying to pin down sources of radio static that interfered with trans-Atlantic telephone transmissions. He identified three different kinds of noise. The first two were related to nearby and distant storms.

Jansky built the directional antenna pictured above to measure the radio static. He called it his “merry-go-round” because it could rotate on a set of wheels from a Model-T. Using the antenna he initially found that the third source of radio hiss seemed to be coming from the sun.

But the source seemed to have moved after a few months, and the fact that it didn't diminish during the eclipse conclusively ruled out the sun. Instead, the source appeared to be in Sagittarius, and its peaks were timed with the sidereal period of 23 hours and 56 minutes.

This led Jansky to conclude that the source must be near the center of the Milky Way, which Jan Oort had pinpointed just 5 years earlier. He published “Electrical disturbances apparently of extraterrestrial origin” the following year.
https://ui.adsabs.harvard.edu/abs/1933PA.....41..548J/abstract

Jansky wanted to build a big radio dish to refine his observations, but his bosses at Bell felt like they had the answers they needed. The project was closed, and Jansky went on to other projects. He passed away in 1950 at the young age of 44.

Many years later, at a ceremony dedicating a sculpture at the site of the original antenna, Jansky’s sister remarked that his persistence probably came from their father always telling them as children to "question everything."

“Star noise”