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
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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More from @mcnees

Oct 8, 2018
Good afternoon.
Happy Dogtober.
Botticelli’s “The Birth of Venus” but it’s a poodle.
Read 4 tweets
Oct 7, 2018
The physicist Niels Bohr was born #OTD in 1885. He applied Planck’s new ideas about quanta to develop the first modern model of atomic structure in 1913, which motivated the development of quantum mechanics over the next few decades.
Inage: Atomic Heritage Foundation
Here’s a thread from last year about the historical context for his model, and how it set physicists on the path to quantum mechanics.
A story about Bohr. In 1939, Rosenfeld told the Princeton Physics Journal Club about his work with Bohr on fission, after Meitner & Frisch's discovery but before its publication. Bohr quickly wrote a letter to Nature asserting priority of Meitner & Frisch. nature.com/articles/14333…
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Oct 5, 2018
Jason Van Dyke found guilty of 2nd degree murder and multiple counts of aggravated battery with a firearm.
All 16 counts of aggravated battery. One for each shot.
Not guilty of Official Misconduct, apparently?
Read 4 tweets
Oct 4, 2018
Koba & Takeda submitted their paper "Radiation Reaction in Collision Processes, III" to the journal Progress of Theoretical Physics #OTD in 1948. It described a method for calculating certain quantities in quantum electrodynamics via "transition diagrams." academic.oup.com/ptp/article/4/…
Their paper was submitted just two days before Freeman Dyson's ground-breaking article on Feynman diagrams was submitted to Physical Review. The approaches are very similar, as was clear to all three scientists!
Upon learning of their results, Dyson amended his own paper to recognize their work. He lamented the effect of the war on the dissemination of important ideas: "The isolation of these Japanese workers has undoubtedly constituted a serious loss to theoretical physics."
Read 4 tweets
Oct 4, 2018
He took out a full page ad in the newspaper demanding the death penalty for five black kids who turned out to be innocent, and still insisted on their guilt even after the real perpetrator confessed.
Here is the ad Trump placed in all four of New York’s major newspapers, months before the end of the trial, when I’d assume presumption of innocence would still apply.
Then in 2014 he *wrote an op-ed* in the Daily News saying they were probably still guilty, even though someone else confessed to the crime.
Read 4 tweets
Oct 4, 2018
Sputnik 1, the first satellite made by humans, was launched into low Earth orbit #OTD in 1957.
The launch of Sputnik marked the beginning of the Space Age. Here, let a young Jeff Goldblum show you what the mood was like in the Pentagon.
Before young squire Goldblum was warning us about the perils of toying with dinosaur DNA (@SUEtheTrex), he was racing down the hallways of the Pentagon with the latest bit of intel on the threat from above.
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