SANTé/MEDECINE - Le fonctionnement de l'oeil humain - La pupille

De face, l'œil présente son iris coloré qui possède une ouverture au centre, la pupille, qui laisse passer la lumière dans l'œil. Autour de l'iris, le blanc de l'œil est peu vascularisé.

© Patrick J. Lynch, CC by 2.5

ASTRONOMY - The Changing Ion Tail of Comet Pons-Brooks

 2024 April 8

The Changing Ion Tail of Comet Pons-Brooks
Image Credit & Copyright: Shengyu Li & Shaining

Explanation: How does a comet tail change? It depends on the comet. The ion tail of Comet 12P/Pons–Brooks has been changing markedly, as detailed in the featured image sequenced over nine days from March 6 to 14 (top to bottom). On some days, the comet's ion tail was relatively long and complex, but not every day. Reasons for tail changes include the rate of ejection of material from the comet's nucleus, the strength and complexity of the passing solar wind, and the rotation rate of the comet. Over the course of a week, apparent changes even include a change of perspective from the Earth. In general, a comet's ion tail will point away from the Sun, as gas expelled is pushed out by the Sun's wind. Today, Pons-Brooks may become a rare comet suddenly visible in the middle of the day for those able to see the Sun totally eclipsed by the Moon.

SANTé/MEDECINE - Le fonctionnement de l'oeil humain - Le système lacrymal

Le système lacrymal comprend :une glande lacrymale ;

des conduits.

La glande lacrymale sécrète une solution saline (les larmes), qui contient du mucus, des anticorps et une enzyme antibactérienne appelée « lysozyme ». Les conduits transportent le liquide lacrymal. Le clignement des yeux pousse les larmes vers le bas.

© FML, CC by-sa 2.5

SANTé/MEDECINE - Histoire - 1895 : découverte des rayons X par Röntgen

Wilhelm Röntgen, physicien allemand, découvrit les rayons X, ce qui lui valut de recevoir le premier prix Nobel de physique en 1901. Cette radiographie représente la main d'Anna Bertha Ludwig Röntgen (son épouse) ; elle a été prise le 22 décembre 1895.

© Wilhelm Röntgen, 1895

FuturaSciences

ASTRONOMY - A Total Solar Eclipse over Wyoming

 2024 April 7

A Total Solar Eclipse over Wyoming
Image Credit & Copyright: Ben Cooper

Explanation: Will the sky be clear enough to see the eclipse? This question is already on the minds of many North Americans hoping to see tomorrow's solar eclipse. This question was also on the mind of many people attempting to see the total solar eclipse that crossed North America in August 2017. Then, the path of total darkness shot across the mainland of the USA from coast to coast, from Oregon to South Carolina -- but, like tomorrow's event, a partial eclipse occurred above most of North America. Unfortunately, in 2017, many locations saw predominantly clouds. One location that did not was a bank of the Green River Lakes, Wyoming. Intermittent clouds were far enough away to allow the center image of the featured composite sequence to be taken, an image that shows the corona of the Sun extending out past the central dark Moon that blocks our familiar Sun. The surrounding images show the partial phases of the solar eclipse both before and after totality.

SANTé/MEDECINE - Le fonctionnement de l'oeil humain - La synthèse additive

Le principe de la synthèse additive est de reconstituer l'apparence des couleurs en additionnant, selon certaines proportions, des lumières provenant de trois sources monochromatiques. Ces trois couleurs primaires chez l'œil humain sont, en fonction des longueurs d'ondes utilisées par les cônes de la rétine :

le rouge ;

le bleu ;

le vert.

© gt

FuturaSciences

SANTé/MEDECINE - HISTOIRE - 1885 : découverte du vaccin contre la rage par Louis Pasteur

Voici la plus célèbre représentation de Louis Pasteur (1822-1895). Grâce à ses travaux sur la rage à la fin de sa vie, Louis Pasteur aurait vacciné un jeune berger alsacien qui avait été mordu par un chien enragé. Ce fut le premier cas de vaccination sur l'Homme, une technique qui avait fait ses preuves sur le mouton contre la maladie du charbon (1881).

© Albert Edelfelt, 1885

FuturaSciences

ASTRONOMY - Unwinding M51

 2024 April 6

Unwinding M51
Image Credit & Copyright: Data - Hubble Heritage Project, Unwinding - Paul Howell

Explanation: The arms of a grand design spiral galaxy 60,000 light-years across are unwound in this digital transformation of the magnificent 2005 Hubble Space Telescope portrait of M51. In fact, M51 is one of the original spiral nebulae, its winding arms described by a mathematical curve known as a logarithmic spiral, a spiral whose separation grows in a geometric way with increasing distance from the center. Applying logarithms to shift the pixel coordinates in the Hubble image relative to the center of M51 maps the galaxy's spiral arms into diagonal straight lines. The transformed image dramatically shows the arms themselves are traced by star formation, lined with pinkish starforming regions and young blue star clusters. Companion galaxy NGC 5195 (top) seems to alter the track of the arm in front of it though, and itself remains relatively unaffected by this unwinding of M51. Also known as the spira mirabilis, logarthimic spirals can be found in nature on all scales. For example, logarithmic spirals can also describe hurricanes, the tracks of subatomic particles in a bubble chamber and, of course, cauliflower.

SANTé/MEDECINE - Fonctionnement de l'oeil humain - Schéma d'une coupe transversale de l'œil

Sur ce schéma d'une coupe transversale de l'œil, on voit le cristallin, qui est la lentille de cet organe sensoriel. Il sépare l'œil en un segment antérieur (à l'avant) et un segment postérieur (à l'arrière).

L'œil comprend des milieux transparents :cristallin ;

humeur aqueuse avant le cristallin ;

humeur vitrée après le cristallin.

La cornée est la partie de la sclérotique (ou sclère) transparente située à l'avant de l'œil.

© Rhcastilhos, DP

FuturaSciences

ASTRONOMY - The Solar Corona Unwrapped

 2024 April 5

The Solar Corona Unwrapped
Image Credit & Copyright: Peter Ward (Barden Ridge Observatory)

Explanation: Changes in the alluring solar corona are detailed in this creative composite image mapping the dynamic outer atmosphere of the Sun during two separate total solar eclipses. Unwrapped from the complete circle of the eclipsed Sun's edge to a rectangle and mirrored, the entire solar corona is shown during the 2017 eclipse (bottom) seen from Jackson Hole, Wyoming, and the 2023 eclipse from Exmouth, Western Australia. While the 2017 eclipse was near a minimum in the Sun's 11 year activity cycle, the 2023 eclipse was closer to solar maximum. The 2023 solar corona hints at the dramatically different character of the active Sun, with many streamers and pinkish prominences arising along the solar limb. Of course, the solar corona is only easily visible to the eye while standing in the shadow of the Moon.