Jacques Philippe Marie Binet was born #OTD in 1786. A French mathematician, physicist, and astronomer. The Binet equation reformulates the law of motion for a central force, with a simple solution to the Kepler problem. en.wikipedia.org/wiki/Jacques...

Pour le troisième cours, j’aborde la physique du milieu atomique, qu’on nomme HI en référence à la notation spectroscopique de l’hydrogène atomique neutre. Présent sous différentes phases thermodynamiques, le gaz atomique est une étape essentielle vers la formation stellaire.

Emilio Segrè was born #OTD in 1905. He discovered technetium and astatine and was awarded the 1959 Nobel Prize for the discovery of the antiproton. His photographs documenting the history of modern physics are hosted at the AIP. en.wikipedia.org/wiki/Emilio_...

Irving Langmuir was born #OTD in 1881. An American physicist, chemist, and engineer, he is mostly known for his work on surface chemistry, with the Langmuir model describing the isothermal adsorption of a gas on a solid. en.wikipedia.org/wiki/Irving_...

Mohammad Abdus Salam was born #OTD in 1926. A Pakistani theoretical physicist, he shared the 1979 Nobel prize with S. Glashow and S. Weinberg for the electroweak unification, and he made significant contributions towards GUT. en.wikipedia.org/wiki/Abdus_S...

Auguste Piccard was born #OTD in 1884. A Swiss physicist, he broke altitude records in a pressurized gondola in order to study cosmic radiation. He then turned to the exploration of large depths, building the first bathyscaphe. en.wikipedia.org/wiki/Auguste...

Beatrice Hill Tinsley was born #OTD in 1941. The first woman to be appointed professor of astronomy at Yale, she made fundamental contributions to the understanding of the chemical evolution of galaxies and their stellar populations. en.wikipedia.org/wiki/Beatric...

Balthasar van der Pol was born #OTD in 1889. A Dutch physicist, he developed an analysis of coupled differential equations in electrical systems, leading to the Van der Pol oscillator, which includes a non-linear damping term. en.wikipedia.org/wiki/Balthas...

Émile Clapeyron was born #OTD in 1799. He was one of the founders of thermodynamics. The Clapeyron relation gives the equilibrium curve between two phases as a function of the latent heat and volume change. en.wikipedia.org/wiki/Beno%C3...

Polykarp Kusch was born #OTD in 1911. He was awarded half of the 1955 Nobel Prize in physics for his measurement of the anomalous spin magnetic moment of the electron, an effect understood in terms of loop corrections in QED. en.wikipedia.org/wiki/Polykar...

Ilya Prigogine was born #OTD in 1917. He made important contributions to the understanding of systems far from thermodynamical equilibrium, in particular regarding the description of dissipative structures that appear in these systems. en.wikipedia.org/wiki/Ilya_Pr...

Joseph-Louis Lagrange was born #OTD in 1736. He made vast contributions to number theory and analysis. He is also the father of analytical mechanics, which is a highly powerful variational formulation of classical mechanics. en.wikipedia.org/wiki/Joseph-...

Ernst Abbe was born #OTD in 1840. A German physicist, he developed many optical systems and coined the term « numerical aperture ». The Abbe number characterizes refractive properties of materials as a function of wavelength. en.wikipedia.org/wiki/Ernst_A...

Hideki Yukawa was born #OTD in 1907. He was the first Japanese physicist to be awarded a Nobel prize, for his prediction of the pion, a particle consisting of a quark and an anti-quark that mediates the nuclear force between nucleons. en.wikipedia.org/wiki/Hideki_...

Paul Langevin was born #OTD in 1872. He developed a stochastic framework for Brownian motion that has a wide range of applications, and a classical theory of paramagnetism. He introduced Einstein’s theory of relativity in France. en.wikipedia.org/wiki/Paul_La...

Lev Landau was born #OTD in 1908. He made fundamental contributions to several domains of theoretical physics, including phase transitions, superconductivity, and superfluidity. He was awarded the 1962 Nobel prize for this latter work. en.wikipedia.org/wiki/Lev_Lan...

George Van Biesbroeck was born #OTD in 1880. A Belgian-American astronomer, he discovered 16 asteroids and 43 double stars. Van Biesbroeck’s star is a red dwarf, notable for its very low luminosity, mass, and temperature. en.wikipedia.org/wiki/George_...

André-Marie Ampère was born #OTD in 1775. He is one of the fathers of electrodynamics, having shown that two electrical wires experience a mutual force. The international unit for electric current is named after him. en.wikipedia.org/wiki/Andr%C3...

Jacobus Kapteyn was born #OTD in 1851. A Dutch astronomer, he measured a large number of stellar parallaxes, magnitudes, and proper motions, developing what may arguably be considered the first model of the Milky Way. en.wikipedia.org/wiki/Jacobus...

Paul Ehrenfest was born #OTD in 1880. An Austrian physicist, he made vast contributions to statistical mechanics and quantum physics. The Ehrenfest theorem states that expectation values of quantum operators behave classically. en.wikipedia.org/wiki/Paul_Eh...

Sophie Kowalevski was born #OTD in 1850. A pioneer for women in mathematics, she generalized Cauchy’s theorem on PDEs. The Kowalevski top is the third and last completely integrable solution of the rigid-body motion problem. en.wikipedia.org/wiki/Sofya_K...

Leo P. Kadanoff was born #OTD in 1937. An American physicist, he explained properties of second-order phase transitions in terms of scaling and universality, leading to applications in a wide variety of fields, including urban planning. en.wikipedia.org/wiki/Leo_Kad...

Wilhelm Wien was born #OTD in 1864. His work on black-body radiation led to a distribution that is correct in the high-frequency limit. The displacement law quantifies the fact that blue stars are hotter than red ones. en.wikipedia.org/wiki/Wilhelm...

Félix Tisserand was born #OTD in 1845. He was the director of the Paris and Toulouse observatories. Tisserand’s parameter is a quasi-invariant used to classify orbits in a subclass of the three-body problem. en.wikipedia.org/wiki/F%C3%A9...

Ányos Jedlik was born #OTD in 1800. A Hungarian priest and physicist, he built devices that may arguably be considered the first electric motor and the first dynamo. He built optical gratings with nanometric spectral resolution. en.wikipedia.org/wiki/%C3%81n...

Katharine Burr Blodgett was born #OTD in 1898. The first woman to be awarded a PhD in Physics from Cambridge, she developed methods to deposit single layers of molecules on a substrate, and study their properties. en.wikipedia.org/wiki/Kathari...

Stephen Hawking was born #OTD in 1942. His contributions to theoretical physics include work on gravitational singularities with R. Penrose, and the proposal that black holes evaporate, a process called « Hawking radiation ». en.wikipedia.org/wiki/Stephen...

Walther Bothe was born #OTD in 1891. The coincidence method reduces false detections in particle detectors, with applications to the Compton effect and the study of comic rays. He also built the first operational cyclotron in Germany. en.wikipedia.org/wiki/Walther...

Johann Philipp Reis was born #OTD in 1834. A German inventor, he is one of the pioneers of the telephone. In 1861, he built a prototype device that captured sound, converted it to electrical impulses, and restituted it. en.wikipedia.org/wiki/Johann_...

Joseph Petzval was born #OTD in 1807. A Hungarian mathematician and physicist, he made important contributions to geometrical optics. The Petzval lens design, which allowed snapshot photography for the first time, is still in use. en.wikipedia.org/wiki/Joseph_...

In the Dutch city of Leiden, physics and astrophysics have become street art, in the form of nine « wall formulas » that adorn buildings. I could not resist filming a train passing in front of this one illustrating the Lorentz length contraction… muurformules.nl

Isaac Newton was born #OTD in 1643. One of the greatest mathematicians and physicists of all time. His mechanics remains the workhorse of physicists in the regimes that do not require a relativistic or quantum mechanical treatment. en.wikipedia.org/wiki/Isaac_N...

Charles Piazzi Smyth was born #OTD in 1819. He made significant contributions to astronomy, in particular pioneering the practice of placing telescopes at high altitudes in order to reduce atmospheric disturbances. en.wikipedia.org/wiki/Charles...

Rudolf Clausius was born #OTD in 1822. A German physicist, he was one of the pioneers of thermodynamics : he introduced the concept of entropy and gave the first statement of the second law. He also introduced the virial theorem. en.wikipedia.org/wiki/Rudolf_...

Satyendra Nath Bose was born #OTD in 1894. Bose-Einstein quantum statistics describe the collective behavior of a set of identical particles of the bosonic type, with applications to lasers, superfluidity, and superconductivity. en.wikipedia.org/wiki/Satyend...

Helen Dodson Prince was born #OTD in 1905. An American astronomer, she was a pioneer in the study of solar flares, doing most of her research at the McMath-Hulbert Observatory, in Michigan. en.wikipedia.org/wiki/Helen_D...

Robert G. Aitken was born #OTD in 1884. An American astronomer working at Lick Observatory, he undertook a systematic study of binary stars, discovering over 3000 new such systems. en.wikipedia.org/wiki/Robert_...

John N. Bahcall was born #OTD in 1934. The discrepancy between his model of the solar neutrino flux and the measured rate, known as the « Solar neutrino problem », is due to neutrinos oscillating between different flavors. en.wikipedia.org/wiki/John_N....

Arthur Eddington was born #OTD in 1882. He led an expedition to observe a Solar eclipse in 1919, which validated Einstein’s GR prediction of the deflection of light. The Eddington luminosity sets an upper limit to accretion. en.wikipedia.org/wiki/Arthur_...

Johannes Kepler was born #OTD in 1571. Based on his thorough observations and those of Tycho Brahe, he formulated the three laws of planetary motion that were later to be derived mathematically from Newton’s theory of gravitation. en.wikipedia.org/wiki/Johanne...

Mary Fairfax Sommerville was born #OTD in 1780. A British polymath, she wrote several landmark books on astronomy and physical sciences. She was the first woman, alongside C. Herschel, to become an honorary member of the RAS. en.wikipedia.org/wiki/Mary_So...

Gerhard Herzberg was born #OTD in 1904. A German-Canadian physicist, he was awarded the 1971 Nobel Prize in Chemistry for his work in molecular spectroscopy, a vital tool to explore the chemical composition of astrophysical objects. en.wikipedia.org/wiki/Gerhard...

James Prescott Joule was born #OTD in 1818. One of the pioneers of thermodynamics, he discovered the relationship between heat and mechanical work, leading to the law of conservation of energy. The Joule is the SI unit of energy. en.wikipedia.org/wiki/James_P...

Vladimir Fock was born #OTD in 1898. A Soviet physicist who contributed to quantum mechanics and gravity theory, he corrected Hartree’s method for calculating approximate wave functions to include Pauli’s exclusion principle. en.wikipedia.org/wiki/Vladimi...

Cécile DeWitt-Morette was born #OTD in 1922. A French mathematician and physicist, she worked on path integrals and black holes. In 1951, she established a summer school in Les Houches, which she led for 22 years. en.wikipedia.org/wiki/C%C3%A9...

Pour le deuxième cours, j’aborde les phases du gaz majoritairement ionisées, qui sont de deux types : le gaz coronal (Hot Ionized Medium, HIM), et le gaz photoionisé associé aux régions HII. Dans ces phases, l’ionisation est due respectivement aux collisions et au rayonnement.

Albert Abraham Michelson was born #OTD in 1852. The first American to receive a Nobel prize in Physics, in 1907, he showed the invariance of the speed of light in different reference frames, in contradiction with the aether theory. en.wikipedia.org/wiki/Albert_...

Joseph John Thomson was born #OTD in 1856. His discovery of the electron in 1897 was the first observation of a subatomic particle. He was awarded the 1906 Nobel Prize for his work on the conduction of electricity in gases. en.wikipedia.org/wiki/J._J._T...

Émilie du Châtelet was born #OTD in 1706. She translated Newton’s « Principia » in French and contributed to the diffusion of Leibniz’s ideas in France. She is considered the first woman scientist in France. en.wikipedia.org/wiki/%C3%89m...

Walther Meissner was born #OTD in 1882. The Meissner effect, which he discovered in 1933, is the expulsion of magnetic field lines from superconducting materials, and is often illustrated by levitating magnets over superconductors. en.wikipedia.org/wiki/Meissne...