Discover and read the best of Twitter Threads about #OTD

Most recents (24)

🕯#OTD Oct 7, 2006: Russian journalist Anna Politkovskaya murdered to silence her fierce voice on Putin mafia state corruption, atrocities, propaganda. Her truth is louder today: Putin's guard dogs hurtling Russia back to USSR abyss…Journalists risk death, bullet, poison, trial.
#Politkovskaya was a journalist & human rights activist, not distinct in authoritarian Russia. Anna said journalists owe duty to tell the truth about the state. One last investigation was into mass poisoning of Chechen schoolchildren, authorities gaslighted as media mass hysteria
Before Trump, Americans might've read #Politkovskaya reports of gaslighting officials who blame media hysteria to cover up the poisoning of schoolchildren as absurd. We see now that gaslighting propaganda is a hallmark of illegitimate authoritarian states.…
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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.…
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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."…
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."
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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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Maria Mitchell snuck out of a party #OTD in 1847, so she could do some observing from the roof of her family's home. She spotted a comet with their 2-inch reflector, which she carefully observed for a few more days before her father notified a friend at the Harvard Observatory.
Sneaking out of a party to do some science is pretty much my signature move, so I have always felt a great fondness for this discovery.
King Frederick VI of Denmark, who had offered a prize for the next astronomer to discover a comet, awarded her a gold medal the following year. It read "Not in vain do we watch the setting and rising of the stars."…
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The National Aeronautics and Space Administration began operations #OTD in 1958. Congress had passed the act creating it on July 16 of that year, with President Eisenhower signing it a few weeks later.
That video is a little bit much with the guitar, so here is a short history put together by former NASA Chief Historian Steven J. Dick and NASA History Web Curator Steve Garber.
Happy 60th birthday, @NASA.
Images: NASA / Project Apollo Archive (…)
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Astrophysicist Dr. George Carruthers was born #OTD in 1939. He developed an ultraviolet spectrograph, launched on a sounding rocket in 1970, that confirmed the existence of interstellar hydrogen, and a similar device placed on the moon by Apollo 16.
Image: US Naval Research Lab
The Apollo 16 mission delivered the Far Ultraviolet Spectrograph designed by Dr. Carruthers to the moon. It is the small object behind astronaut John Young in this photo taken at the Descartes landing site.
Image: NASA / Charles Duke, Jr.
In 2012, Dr. Carruthers was awarded the National Medal of Technology and Innovation.
Image: US Naval Research Lab
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Enrico Fermi, one of the foremost experimental and theoretical physicists of the 20th century, was born #OTD in 1901. Now estimate how many other physicists were born on that day.
Image: New York Public Library
Fermi was only 21 when he completed his PhD at Pisa, and after a few years abroad working with Born and Ehrenfest he became a lecturer at Florence. It was there that he worked out the statistics of a collection of particles satisfying Pauli's exclusion principle.
Fundamental particles like leptons and quarks, as well as composite particles like protons and neutrons, satisfy these Fermi-Dirac statistics (Dirac obtained the same results a few months after Fermi). For this reason, we refer to this broad class of particles as Fermions.
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Astronomer and mathematician Pierre-Louis Moreau de Maupertuis, exact date of birth unknown, was born around this time in 1698 and baptized #OTD. He was among the first to articulate the principle of least action, one of the most beautiful ideas in physics.
Image: Wellcome Trust
Maupertuis originally formulated his principle to explain the motion of light, arguing that the integral of its velocity along the path it follows is minimized. This allowed him to recover Snell's Law for the refraction of light as it passes between different materials.
By 1744, Maupertuis extended this idea to the motion of material objects. He defined an object's “action" as the integral of momentum along its path, or the time integral of its "vis viva" (kinetic energy) from start to finish. He proposed that Nature acts to minimize the action.
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It’s the formula we all know: E = mc².

Einstein submits his second special relativity manuscript, in which he proposes mass-energy equivalence, to Annalen der Physik #OTD in 1905. His first SR paper had appeared the previous day.

An English translation:…
Einstein wasn’t the first to propose a relationship between changes in an object’s energy and its inertia. But afaik he was the first to propose that the relationship goes beyond energy lost to radiation, as well as get the correct form of the equivalence.
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The astrophysicist Charlotte Moore Sitterly, who compiled extensive data on optical and later UV spectra, was born #OTD in 1898. Her spectroscopic tables are still in use today.
Image: AIP Emilio Segrè Visual Archives, Gift of Michael A. Duncan
"She was a brilliant scientist."
In 2010, Vera Rubin published her recollections of Charlotte Moore Sitterly in the Journal of Astronomical History and Heritage.…
The AIP also has an oral history with Charlotte Moore Sitterly, from a 1978 interview by David DeVorkin.…
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The physicist Clifford Shull, who developed techniques for studying the structure of matter via neutron diffraction, was born #OTD in 1915.
Image: ORNL
Some of the papers and lab notebooks from the neutron scattering experiments performed by Clifford Shull and Ernest Wollan in the late 1940s and early 1950s, on display at @ORNL's Shull Wollan Center
Image: ORNL
Just bombarding matter with neutrons and looking at the resulting diffraction pattern to understand how stuff is made, nbd.
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Michael Faraday, who made foundational discoveries about electromagnetism and was an inspiration for both Maxwell and Einstein, was born #OTD in 1791.
Portrait: Thomas Phillips
Here’s a thread from last month about Faraday’s discovery of induction, and his sophisticated ideas about “lines of force” that anticipated the modern notion of fields.
And a longer thread about Faraday from last year, about his life and work.
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The Voyager 1 spacecraft, 7.25 million miles away and speeding towards Jupiter, looked homeward #OTD in 1977 and captured the first picture of the whole Earth and Moon together in the same frame.
Image: NASA / JPL
Yes, by all means, if you’re a billionaire with the opportunity please send artists to the moon. Send poets, painters, and writers. Send folks who’ll see the moon growing large, the Earth small and flawless, and find perspectives that frame our place in the vast, lonesome cosmos.
Twelve-and-a-half years passed between this view, and Sagan and colleagues thinking to turn Voyager 1’s cameras back towards Earth to capture a solar system mosaic that included the Pale Blue Dot photo.
Images: NASA / JPL
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The mathematician Bernhard Riemann was born #OTD in 1826. He made deep contributions to complex analysis and number theory, but is best remembered by physicists for his work on the foundations of geometry that would provide the mathematical framework for general relativity.
Riemann was the star pupil of Gauss, who described Riemann's PhD thesis on complex variables as the work of someone with “a gloriously fertile originality.”
A few years later, when Riemann was up for a faculty position, Gauss tasked him with reformulating the foundations of geometry. Riemann's lecture "On the Hypotheses Which Lie at the Foundations of Geometry" was delivered in 1854. Here's a thread:
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To mark the 40th anniversary of the #CampDavidAccords, check out our collection of more than 250 documents--totaling more than 1,400 pages--of intelligence provided to President Carter leading up to the Sept. 1978 Middle East Peace Accords at Camp David.
After 12 days of talks at Camp David, Israeli Prime Minister Menachem Begin & Egyptian President Anwar Sadat signed the #CampDavidAccords on Sept. 17, 1978.

The declassified documents in CIA’s collection cover the period from January 1977 through March 1979 & detail diplomatic developments throughout the region following the #CampDavidAccords.

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Glashow submitted "Partial-Symmetries Of Weak Interactions"#OTD in 1960, an important step towards electroweak unification. It answered the question: How can there be a symmetry between electromagnetism and the weak interaction if one conserves parity but the other does not?
Electromagnetism is based on the exchange of the photon, a massless and electrically neutral vector boson. Schwinger had proposed in the late 1950s that weak interactions were mediated by the exchange of two charged and massive vector bosons called the W^{+} and W^{-}.
Electromagnetic interactions (as well as gravity and the strong interaction, as far as we know) conserve parity. That means the rules work the same way and produce the same results if we replace everything with its mirror reflection.
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Epidemiology pioneer John Snow, who doubted the prevailing miasma theory for the spread of a cholera outbreak in London, traced infections and spoke to locals to pinpoint a public water pump as the source. He removed its handle #OTD in 1854, helping put an end to the outbreak. Portrait of John Snow by Thomas Jones Barker
You can see the famous “ghost map” (which was made later) of the outbreak here, a foundational document of data visualization pinpointing the pump as the culprit. @EdwardTufte…
Unfortunately, Twitter rules require you to RT before you can make a Game Of Thrones reference.
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Physicist James Van Allen was born #OTD in 1914. His 1958 satellite experiments (Explorer 1 and 3, Pioneer 3) revealed the Van Allen Radiation Belts: donut shaped regions where charged particles captured from the solar wind are trapped by Earth’s magnetic field.
Images: AAS, NASA
A lesser known fact is that, for some reason, my family used to have a picnic table built by Van Allen and some other scientists. His name was carved on the bottom with a wood-burning tool. Idk where we got it, but when my parents sold their lake cabin the table went with it.
Van Allen was also an early advocate for getting scientific experiments on satellites and rockets: first with captured V-2 rockets after the war, then his rocket-assisted balloons dubbed “rockoons“, and finally satellites launched by the US space program.
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The space probe Voyager 1, now the most distant human-made object, was launched from NASA’s Kennedy Space Center at Cape Canaveral #OTD in 1977. It is currently 13.3 billion miles from Earth, racing away from us at over 38,000 miles per hour.
NASA released these posters last year to commemorate the 40th anniversary of the Voyager missions. However, it turns out you can STILL look at them EVEN TODAY. Go enjoy these posters.
Image: NASA/JPL-Caltech
"I'd love to hear more about what's happening back on Earth, like the extremist shadow government running a coup against the amoral toddler in the White House. But the thing is, I'm only like 13.3 billion miles away, and frankly that doesn't feel far enough. Byeeeee." –Voyager 1
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The astrophysicist Dr. Jaqueline Hewitt, known for her pioneering work on gravitational lensing, was born #OTD in 1958. In 1987 she led the team of observers at the Very Large Array that discovered the first Einstein ring.
Images: Hewitt et al, Nature 333, 537 (1988)
We see an Einstein ring when light rays from a distant source are gravitationally lensed by a massive object in the foreground, so that the source of the light appears ring-like in shape. It requires a delicate alignment of the source, the lensing object, and the Earth.
Einstein himself was skeptical about the prospects of seeing a ring. He imagined both the source and the lensing object to be pointlike. In that case, the precise alignment needed to form a complete ring just seemed too unlikely.
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John Dalton made an entry into his logbook #OTD in 1803 that introduced a set of symbols to represent elements. His system, which was the first to use symbols, was replaced about a decade later by the modern notation introduced by Berzelius.
It is an unconscionable failure of modern science, that there is no metal with chemical symbol “Af”
Scientist 1: What do the tests say? How metal is the compound?

Scientist 2: Well, it is metal Af.
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The first solar flare observations were made #OTD in 1859 by Carrington & Hodgson, preceding one of the largest geomagnetic storms on record. Both amateur astronomers made their observations independently, and published them simultaneously in MNRAS.…
The solar storm that followed was one of the most intense on record. Auroras were reported all over the world and there were mass telegraph outages. Currents induced in the telegraph lines were strong enough to melt contacts, shock operators, and set some kinds of paper on fire.
A “Carrington-class” solar storm occurred in 2012, but the coronal mass ejection from that one just missed the Earth.
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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.
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