Tycho Brahe was born #OTD in 1546. His astronomical observations were the most accurate of his time, before the advent of telescopes. With these observations, J. Kepler would go on to develop his three laws of planetary motion. en.wikipedia.org/wiki/Tycho_B...

Kristian Birkeland was born #OTD in 1867. By studying the influence of magnets on electron beams, he elucidated the nature of polar auroræ as originating from solar particles interacting with the Earth’s magnetic field. en.wikipedia.org/wiki/Kristia...

Je donne depuis quelques années un cours de M2 consacré au milieu interstellaire et à la formation des étoiles. Hier matin avait lieu la première des sept séances pour 2025-2026, et je me suis dit que c'était l'occasion de faire un peu de vulgarisation sur ces thématiques.

Contrairement à ce qu'on peut imaginer, le milieu interstellaire (MIS) est loin d’être vide ! C’est un mélange de gaz, de poussières et de particules relativistes, traversé de rayonnements électromagnétiques, agité de mouvements turbulents et baigné de champs magnétiques.

Max Born was born #OTD in 1882. One of the German pioneers of quantum mechanics, he provided the probabilistic interpretation of the wave function and of its projection on eigenspaces of the operators that represent physical quantities. en.wikipedia.org/wiki/Max_Born

Annie Jump Cannon was born #OTD in 1863. A member of the « Harvard computers », she manually classified more stars than anyone else (around 350000), and the classification scheme she devised is the base of the one still in use. en.wikipedia.org/wiki/Annie_J...

Leo James Rainwater was born #OTD in 1917. He was awarded the 1975 Nobel Prize in Physics together with A. Bohr and B. Mottelson for their work on the spheroidal shell model of atomic nuclei. He also worked on muonic atoms. en.wikipedia.org/wiki/James_R...

Peter Andreas Hansen was born #OTD in 1795. A Danish-born German astronomer and long-time director of Gotha observatory, he worked on lunar theory, Jupiter-Saturn perturbations, and cometary disturbances. en.wikipedia.org/wiki/Peter_A...

Gerard Kuiper was born #OTD in 1905. He suggested that small planets and comets may have originated in the outskirts of the solar system, beyond the orbit of Neptune, although he did not believe this « Kuiper belt » to exist still. en.wikipedia.org/wiki/Gerard_...

Joseph Louis Gay-Lussac was born #OTD in 1778. Together with Humboldt, he discovered that water is made of two parts hydrogen and one part oxygen. The « degrees Gay-Lussac » are used to measure alcohol concentration. en.wikipedia.org/wiki/Joseph_...

Werner Heisenberg was born #OTD in 1901. He developed the matrix formulation of quantum mechanics, giving a mathematical ground to the uncertainty principle stating that some observables can never be known exactly simultaneously. en.wikipedia.org/wiki/Werner_...

Arnold Sommerfeld was born #OTD in 1868. A German theoretical physicist, he made vast contributions to many fields such as fluid mechanics and optics, and he pioneered the development of early quantum physics. en.wikipedia.org/wiki/Arnold_...

Quelle triste nouvelle ! Karim avait tant contribué à l’analyse des données Planck, et il travaillait maintenant sur Euclid. Il était également enseignant au M2 AADC. J’adresse mes plus sincères condoléances à ses proches.

La communauté @iap.fr a l'immense tristesse de vous annoncer la disparition brutale de Karim Benabed, dans un accident de la circulation, hier après-midi, le 3 décembre.

Ernst Chladni was born #OTD in 1756. A pioneer of acoustics, he is mostly known for devising a method to visualize the modes of vibration of rigid plates. He also proposed that meteorites were of extraterrestrial origin. en.wikipedia.org/wiki/Ernst_C...

Christian Doppler was born #OTD in 1803. He postulated that the perceived frequency of a wave depends on the relative velocities of the emitter and receiver, an effect H. Fizeau subsequently established mathematically. en.wikipedia.org/wiki/Christi...

Lars Onsager was born #OTD in 1903. The Onsager relations put constraints on the linear response (e.g., heat flux) to imbalances in thermodynamic properties. He also provided the analytic solution to the 2D Ising model in zero field. en.wikipedia.org/wiki/Lars_On...

Jean-Jacques d'Ortous de Mairan was born #OTD in 1678. Mostly known as a chronobiologist, he was also an astronomer, observing a nebulosity in Orion (M43), and suggesting that auroræ were caused by the Sun. en.wikipedia.org/wiki/Jean-Ja...

Julius Robert von Mayer was born #OTD in 1814. He gave one of the first statements of the first law of thermodynamics, suggesting work and heat to be different forms of energy that can nonetheless be converted into one another. en.wikipedia.org/wiki/Julius_...

Simon van der Meer was born #OTD in 1925. A Dutch physicist, he was awarded the Nobel Prize in 1984 for the experimental discovery, using CERN’s SPS, of the W and Z bosons that mediate the weak interaction. en.wikipedia.org/wiki/Simon_v...

Johannes van der Waals was born #OTD in 1837. The van der Waals forces are intermolecular interactions, while the equation of state explains the gas-liquid transition and the existence of metastable states. en.wikipedia.org/wiki/Johanne...

Louis Néel was born #OTD in 1904. His studies of magnetism, in particular antiferromagnetism and ferrimagnetism, earned him the 1970 Nobel Prize. After WWII, he led the development of the scientific activity in the Grenoble area. en.wikipedia.org/wiki/Louis_N...

Edwin Hubble was born #OTD in 1889. By observing Cepheids in Andromeda, he showed that many « nebulae » are actually external galaxies. The Hubble-Lemaître law between redshift and distance implies the expansion of the Universe. en.wikipedia.org/wiki/Edwin_H...

Eleanor Helin was born #OTD in 1932. She headed JPL’s Near-Earth Asteroid Tracking program, discovering over 900 minor solar system bodies (asteroids from the Apollo, Amor, and Trojan families, and several comets). en.wikipedia.org/wiki/Eleanor...

Patrick Blackett was born #OTD in 1897. He showed that elements could be transmuted by bombarding them with alpha particles. He also studied cosmic rays using cloud chambers, and made contributions to paleomagnetism. en.wikipedia.org/wiki/Patrick...

Jean le Rond d’Alembert was born #OTD in 1717. A French polymath, his research in physics is mostly associated with waves and fluid dynamics. He also authored many articles for Diderot’s « Encyclopédie ». en.wikipedia.org/wiki/Jean_le...

William Herschel was born #OTD in 1738. Using large reflector telescopes of his own design, he discovered Uranus and many solar system bodies. He was also a pioneer of spectrophotometry, discovering infrared radiation. en.wikipedia.org/wiki/William...

Demain samedi 15 novembre, à 15h, j’aurai le plaisir de parler de la vie et de la mort des étoiles à la médiathèque d’Arc-en-Barrois (Haute-Marne), à l’invitation de l’association « Arc Patrimoine & Culture ».

John W. Strutt, Lord Rayleigh, was born #OTD in 1842. His many contributions, most notably in fluid mechanics, optics, and acoustics, are reflected in the large number of phenomena and laws that bear his name. en.wikipedia.org/wiki/John_Wi...

Mildred Spiewak Dresselhaus was born #OTD in 1930. During her extensive career at MIT, she dedicated a great part of her research to the properties of nanostructures (fullerenes and nanotubes), ushering in new technologies. en.wikipedia.org/wiki/Mildred...

Carl Sagan was born #OTD in 1934. A pioneer of exobiology, he assembled messages on the Pioneer and Voyager probes and was an early advocate for SETI. He was an outspoken science communicator, writing many books for the general public. en.wikipedia.org/wiki/Carl_Sa...

Johannes Rydberg was born #OTD in 1854. The Rydberg formula gives the wavelength of light for an electronic transition in hydrogen atoms. In a Rydberg state, one electron is highly excited, making the spectrum hydrogen-like. en.wikipedia.org/wiki/Johanne...

Edmund Halley was born #OTD in 1656. The second Astronomer Royal, he catalogued the southern hemisphere and computed the periodicity of the comet that bears his name. He demonstrated that stars, far from fixed, undergo proper motions. en.wikipedia.org/wiki/Edmond_...

Marie Skłodowska-Curie was born #OTD in 1867. One of the most prominent scientists of her time, she pioneered studies of radioactivity, coining the term and discovering two new chemical elements, polonium and radium. en.wikipedia.org/wiki/Marie_C...

Fred Lawrence Whipple was born #OTD in 1906. He discovered several comets, hypothesizing that their composition was that of an icy conglomerate. He also designed a device to protect spacecraft from the impact of small particles. en.wikipedia.org/wiki/Fred_La...

Charles K. Kao was born #OTD in 1933. His work on optical fibers proved that attenuation could be significantly reduced by using high-purity fused silica, opening the path to the wide use of this technology in modern communications. en.wikipedia.org/wiki/Charles...

Alfred Perot was born #OTD in 1863. Together with C. Fabry, he invented a new high-precision, N-wave interferometer made of two semi-reflective plates. The Fabry-Perot interferometer had many applications in spectroscopy. en.wikipedia.org/wiki/Alfred_...

Harlow Shapley was born #OTD in 1885. Initially opposed to Hubble’s idea that « spiral nebulæ » were galaxies like our own, rather than Galactic objects, he later defended the idea that they are organized in superclusters. en.wikipedia.org/wiki/Harlow_...

Hermann Bondi was born #OTD in 1919. An Austrian-British cosmologist, he defended the steady-sate model with F. Hoyle and T. Gold. He also explained the nature of gravitational waves and worked on accretion onto compact objects. en.wikipedia.org/wiki/Hermann...

#Publicité #Famille Une fiction interactive jouée, captée et diffusée en direct sur Twitch, Youtube, Arte.tv mais aussi dans 25 salles de cinéma simultanément, c’est « Les Burgers Sanglants » et c’est ce vendredi 31 octobre à 19h.

Galileo Ferraris was born #OTD in 1847. An Italian physicist and electrical engineer, he worked on induction processes, building one of the first polyphase alternators, although he never patented his work, unlike N. Tesla. en.wikipedia.org/wiki/Galileo...

Homi Bhabha was born #OTD in 1909. He computed the cross-section of electron-positron scattering and described how primary cosmic rays interact with the atmosphere to produce air showers. Post-WWII, he led the Indian nuclear program. en.wikipedia.org/wiki/Homi_J....

Laura Bassi was born #OTD in 1711. She popularized Newtonian mechanics in Italy. She was one of the first women to earn a PhD and the first to become a teacher at the University of Bologna. en.wikipedia.org/wiki/Laura_B...

Wilhelm Anderson was born #OTD in 1880. A Russian-Estonian astrophysicist, he worked on the mass limit of white dwarf stars, providing a value that is slightly overestimated because of an invalid uniform-density hypothesis. en.wikipedia.org/wiki/Wilhelm...

#Publicité #Famille Une fiction interactive jouée, captée et diffusée en direct sur Twitch, Youtube, Arte.tv mais aussi dans 25 salles de cinéma simultanément, c’est « Les Burgers Sanglants » et c’est ce vendredi 31 octobre à 19h.

Henrietta Hill Swope was born #OTD in 1902. She worked with H. Shapley, then W. Baade, to study variable stars. Using the period-luminosity relation for Cepheids discovered by H. S. Leavitt, she determined the distance to M31. en.wikipedia.org/wiki/Henriet...

Henry Norris Russell was born #OTD in 1877. An American astronomer who devised the HR diagram, paving the way for stellar evolution studies. With F. Saunders, he developed the L-S coupling scheme for spin-orbit interactions. en.wikipedia.org/wiki/Henry_N...

Pierre-Gilles de Gennes was born #OTD in 1932. A specialist of « soft-matter » physics, his work on the properties of polymers and liquid crystals, in particular their phase transitions, earned him the 1991 Nobel Prize. en.wikipedia.org/wiki/Pierre-...

Felix Bloch was born #OTD in 1905. He worked on ferromagnetism, the properties of electrons in solids, and nuclear magnetic induction, for which he received the 1952 Nobel Prize. He was the first Director-General of CERN. en.wikipedia.org/wiki/Felix_B...

Ilya Frank was born #OTD in 1908. He was awarded the Nobel Prize in 1958. The Frank-Tamm formula gives the spectrum of Cherenkov radiation emitted, per unit length, by a charged particle as it moves faster than light in a material medium. en.wikipedia.org/wiki/Ilya_Fr...