On This Day
In astronomy, Kepler’s laws of planetary motion are three scientific laws describing the motion of planets around the Sun.
The orbit of a planet is an ellipse with the Sun at one of the two foci.
A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.[1]
The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.
Most planetary orbits are nearly circular, and careful observation and calculation are required in order to establish that they are not perfectly circular. Calculations of the orbit of Mars[2] indicated an elliptical orbit. From this, Johannes Kepler inferred that other bodies in the Solar System, including those farther away from the Sun, also have elliptical orbits.
Kepler’s work (published between 1609 and 1619) improved the heliocentric theory of Nicolaus Copernicus, explaining how the planets’ speeds varied, and using elliptical orbits rather than circular orbits with epicycles.[3]
Isaac Newton showed in 1687 that relationships like Kepler’s would apply in the Solar System to a good approximation, as a consequence of his own laws of motion and law of universal gravitation.
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Born On This Day
1845 – Élie Metchnikoff, Russian zoologist (d. 1916)
Ilya Ilyich Mechnikov (Russian: Илья́ Ильи́ч Ме́чников, also written as Élie Metchnikoff; 15 May [O.S. 3 May] 1845 – 15 July 1916)[1][note 1] was a Russian[2] zoologist best known for his pioneering research in immunology.[3][4][5]
In particular, he is credited with the discovery of phagocytes (macrophages) in 1882. This discovery turned out to be the major defence mechanism in innate immunity.[6] He and Paul Ehrlich were jointly awarded the 1908 Nobel Prize in Physiology or Medicine “in recognition of their work on immunity”.[7] He is also credited by some sources with coining the term gerontology in 1903, for the emerging study of aging and longevity.[8][9] He established the concept of cell-mediated immunity, while Ehrlich established the concept of humoral immunity. Their works are regarded as the foundation of the science of immunology.[10] In immunology, he is given an epithet the “father of natural immunity”.[11]
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wikimedia
- Wikimedia Commons picture of the day for November 25 November 25, 2024Picture of the day Papaya fruits in a grocery store. Colatina, Espírito Santo, Brazil.
- Wikimedia Commons picture of the day for November 24 November 24, 2024Picture of the day The Scroll of Eighty-Seven Immortals, drawn by an unknown painter, measuring 30cm high and 292cm wide, is a line-drawing Chinese figure painting. Drawn on a long silk scroll with lines, the painting depicts 87 taoist immortals, including three supreme gods with halo, ten divine generals, seven deities and 67 celestial maidens […]
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