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 ruled out the sun as a source. He soon attributed what he called "star noise" to large clouds of ionized gas near the center of the Milky Way.
There wasn't much interest from other scientists at the time. Even Jansky didn't really appreciate that he had invented the field of Radio Astronomy.
Image: Bell Telephone Laboratories
Image: Bell Telephone Laboratories
A little more background: Jansky was working for Bell Labs, studying 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.
He built the directional antenna in that picture to measure the radio static. It could rotate on a set of wheels from a Model-T, and he called it his "merry-go-round." The third sort of radio hiss initially 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 run. 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 (refining earlier estimates by Harlow Shapley) just 5 years before. He published “Electrical disturbances apparently of extraterrestrial origin” the following year.
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 work on other things. 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, his sister remarked that Jansky's persistence probably came from their father always telling them as children to "question everything."
☝️A little thread about the origins of radio astronomy.
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