Alain Picard In summary: Blazars: Extreme Beacons of Active Galactic Nuclei Blazars represent the most exotic class of active galactic nuclei (AGN). They harbor supermassive black holes at the center of giant elliptical galaxies, with masses that can reach several billion times that of our Sun. These cosmic monsters are surrounded by an accretion disk, a dense, … Read more
Microquasars have fascinated astrophysicists since their discovery due to their striking resemblance to quasars, yet situated on much smaller scales. In the heart of our galaxy, these compact objects represent perfect natural laboratories for studying complex astrophysical phenomena, such as relativistic jets and intense variations of X radiation. These entities are primarily composed of a … Read more
Symbiotic stars represent a unique category of binary systems where complex and dynamic astrophysical phenomena intertwine. These pairs of celestial bodies, composed of an evolved red giant and a hotter, more compact star, often a white dwarf, embody deep stellar interactions. This cosmic marriage generates a ballet of material transfer, energy accumulation, and recurrent explosions, … Read more
IN BRIEF Extraterrestrial origin of meteorites and their scientific value. Importance of collection and observation of meteorites. Role of participatory programs like Vigie-Ciel. Study of impacts and craters created by these phenomena. Identification and distinction of meteors and meteorites. Contribution to the understanding of Earth’s geological history. Use of meteorites to understand the composition of … Read more
IN SHORT Natural satellites : celestial objects in orbit around a larger body. Examples : the Moon as a satellite of the Earth. Total number within the Solar system : about 220 satellites. Essential role in the dynamics of planetary systems. Influence on the tides and climates of planets. Study of natural satellites to understand … Read more
IN BRIEF Eclipse: the appearance of a celestial body when another celestial body positions itself in front of it. Solar eclipse: the Moon partially or completely blocks the light of the Sun. Lunar eclipse: the Earth is located between the Sun and the Moon, resulting in a shadow on the latter. Different types of eclipses: … Read more
IN BRIEF Lunar phases: a 29-day cycle with several stages. New Moon: absence of visible light, Moon positioned between the Earth and the Sun. First Quarter: right half of the Moon visible in the northern hemisphere. Full Moon: complete illumination of the surface, fully lit face. Last Quarter: left half visible, transition back to the … Read more
IN BRIEF Asteroids: monitored to assess the risks to Earth. Threats: encountering asteroids a kilometer in diameter can be fatal. Risks: about one threatening asteroid strikes Earth every 600,000 years. Dinosaur extinction: the impact of an asteroid 65 million years ago caused a mass extinction. NASA: regularly observes near-Earth objects and their potential danger. Opportunities: … Read more
IN BRIEF History of comets since antiquity. Notable discoveries of comets and their movements. Recent developments thanks to the Rosetta probe. Scientific challenges related to the formation of comets. Accessible and informative writing style. Impact of comets on modern astronomy. Comets, these mysterious celestial bodies, have fascinated humanity since antiquity with their spectacular appearance and … Read more
IN SHORT Antiquity : Origins of astronomy with the Mesopotamians and the Greeks. 1543 : Nicholas Copernicus proposes the heliocentric model. 17th century : Establishment of the law of gravitation by Isaac Newton. 20th century : Emergence of the Big Bang theory. Contributions from great astronomers like Galileo and Kepler. Evolution of observation instruments and … Read more