François Levrier
@francoislevrier.bsky.social
Professeur d’astrophysique - ENS Paris - Responsable du Master AADC - Coordinateur de l’action thématique PCMI (Physique et Chimie du Milieu Interstellaire)
(Photo ©A. Vergallo)
(Photo ©A. Vergallo)
Pinned
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.
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...
en.wikipedia.org/wiki/Charles...
January 3, 2026 at 8:30 AM
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...
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_...
en.wikipedia.org/wiki/Rudolf_...
January 2, 2026 at 8:53 AM
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_...
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...
en.wikipedia.org/wiki/Satyend...
January 1, 2026 at 8:56 AM
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...
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...
en.wikipedia.org/wiki/Helen_D...
December 31, 2025 at 7:13 AM
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...
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_...
en.wikipedia.org/wiki/Robert_...
December 31, 2025 at 7:13 AM
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_...
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....
en.wikipedia.org/wiki/John_N....
December 30, 2025 at 7:30 AM
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....
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_...
en.wikipedia.org/wiki/Arthur_...
December 28, 2025 at 7:41 AM
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_...
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...
en.wikipedia.org/wiki/Johanne...
December 27, 2025 at 6:58 AM
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...
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...
en.wikipedia.org/wiki/Mary_So...
December 26, 2025 at 6:05 AM
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...
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...
en.wikipedia.org/wiki/Gerhard...
December 25, 2025 at 6:53 AM
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...
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...
en.wikipedia.org/wiki/James_P...
December 24, 2025 at 6:43 AM
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...
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...
en.wikipedia.org/wiki/Vladimi...
December 22, 2025 at 5:54 AM
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...
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...
en.wikipedia.org/wiki/C%C3%A9...
December 21, 2025 at 8:34 AM
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...
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.
December 20, 2025 at 5:47 PM
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_...
en.wikipedia.org/wiki/Albert_...
December 19, 2025 at 5:42 AM
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_...
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...
en.wikipedia.org/wiki/J._J._T...
December 18, 2025 at 6:18 AM
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...
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...
en.wikipedia.org/wiki/%C3%89m...
December 17, 2025 at 5:35 AM
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...
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...
en.wikipedia.org/wiki/Meissne...
December 16, 2025 at 6:23 AM
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...
en.wikipedia.org/wiki/Meissne...
Henri Becquerel was born #OTD in 1852. For his discovery of radioactivity and the study of radioactive elements, he was awarded the 1903 Nobel Prize alongside M. and P. Curie. The Becquerel is the SI unit of radioactivity.
en.wikipedia.org/wiki/Henri_B...
en.wikipedia.org/wiki/Henri_B...
December 15, 2025 at 6:36 AM
Henri Becquerel was born #OTD in 1852. For his discovery of radioactivity and the study of radioactive elements, he was awarded the 1903 Nobel Prize alongside M. and P. Curie. The Becquerel is the SI unit of radioactivity.
en.wikipedia.org/wiki/Henri_B...
en.wikipedia.org/wiki/Henri_B...
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...
en.wikipedia.org/wiki/Tycho_B...
December 14, 2025 at 8:19 AM
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...
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...
en.wikipedia.org/wiki/Kristia...
December 13, 2025 at 7:40 AM
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...
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.
December 12, 2025 at 10:07 AM
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.
December 12, 2025 at 10:04 AM
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
en.wikipedia.org/wiki/Max_Born
December 11, 2025 at 5:41 AM
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
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...
en.wikipedia.org/wiki/Annie_J...
December 11, 2025 at 5:40 AM
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...
en.wikipedia.org/wiki/Annie_J...