ASTRONOMY - Earth During a Total Solar Eclipse

 2020 December 29

Earth During a Total Solar Eclipse
Video Credit: GOES-16, ABI, NOAA, NASA

Explanation: What does the Earth look like during a total solar eclipse? It appears dark in the region where people see the eclipse, because that's where the shadow of the Moon falls. The shadow spot rapidly shoots across the Earth at nearly 2,000 kilometers per hour, darkening locations in its path -- typically for only a few minutes -- before moving on. The featured video shows the Earth during the total solar eclipse earlier this month. The time-lapse sequence, taken from a geostationary satellite, starts with the Earth below showing night but the sun soon rises at the lower right. Clouds shift as day breaks over the blue planet. Suddenly the circular shadow of the Moon appears on the left and moves rapidly across South America, disappearing on the lower right. The video ends as nightfall begins again. The next total solar eclipse will occur next December -- but be visible only from parts of Antarctica.

Coronavirus : oui, on peut laver son masque jetable

Un masque jetable doit être jeté au bout de quatre heures d'utilisation : c'est ce que vous avez entendu partout. Les masques chirurgicaux sont pourtant parfaitement lavables et réutilisables, atteste sur France Bleu Philippe Vroman, enseignant-chercheur au laboratoire Gemtex de l'Ensait à Roubaix. Il faut savoir que le masque chirurgical tire son efficacité de deux points. Premièrement, sa matière, constituée de trois épaisseurs : une couche de meltblown, un textile non tissé très filtrant dérivé du polypropylène, pris en sandwich entre deux couches de spunbond, aux fibres beaucoup plus grosses et servant de matériau support. Deuxièmement, on ajoute sur ce masque une charge électrostatique qui « retient » les particules virales.

Quand on mouille le masque, ce dernier perd sa charge électrostatique : c'est pour cela qu'on conseille de le changer lorsqu'il est humide. « Mais comme ce masque a une efficacité globalement supérieure aux autres masques, même après avoir été lavé et donc perdu sa charge électrostatique, il reste globalement plus efficace que les autres », assure Philippe Vroman. Une fois lavé, le meltblown filtre encore 95 % des particules de moins de trois microns, contre 90 % pour les masques en tissu grand public, explique le spécialiste.

Mais combien de fois est-il réutilisable ? « C'est une bonne question ! Aujourd'hui, on fait des études pour vérifier la capacité de ce masque à être réutilisable. La piste n'avait pas été explorée jusqu'à présent puisque ça n'était pas l'usage du masque chirurgical. Mais comme on a des résultats intéressants jusqu'à cinq lavages, nous allons étudier sa tenue », indique Philippe Vroman. Même en prenant une base de cinq lavages, cela permet de beaucoup réduire le gaspillage, la pollution... et le coût.

Futura Sciences

MUSICA - Verdi - Va piensero

"Va piensero"

 

MUSICA - Feliz Navidad

"FELIZ NAVIDAD"

 

VOLCANOLOGY - A Volcanic Great Conjunction

 2020 December 20

A Volcanic Great Conjunction
Image Credit & Copyright: Francisco Sojuel

Explanation: Where can I see the Great Conjunction? Near where the Sun just set. Directionally, this close passing of Jupiter and Saturn will be toward the southwest. Since the planetary pair, the Sun, and the Earth are nearly in a geometric straight line, the planets will be seen to set just where the Sun had set -- from every location on Earth. When can I see the Great Conjunction? Just after sunset. Since the two planets are so near the Sun directionally, they always appear in the sky near the Sun, but can best be seen when the Earth blocks the Sun but not the planets: sunset. Soon thereafter, Jupiter and Saturn will also set, so don't be late! Is tomorrow night the only night that I can see the Great Conjunction? Tomorrow night the jovian giants will appear the closest, but on any night over the next few days they will appear unusually close. Technically, the closest pass happens on 21 December at 18:20 UTC. Will there be an erupting volcano on the horizon near the Great Conjunction? Yes, for example if you live in Guatemala where the featured image was taken. Otherwise, generally, no. In the featured image captured last week, Jupiter and Saturn are visible toward the right, just above a tree, and bathed in the diffuse glow of zodiacal light.

PRATIQUE - Comment faire fuir les mouches

 

PRATIQUE - Nettoyer facilement clavier PC

 

ASTRONOMY - Conjunction after Sunset

 2020 December 19

Conjunction after Sunset
Image Credit & Copyright: Alireza Vafa

Explanation: How close will Jupiter and Saturn be at their Great Conjunction? Consider this beautiful triple conjunction of Moon, Jupiter and Saturn captured through clouds in the wintry twilight. The telephoto view looks toward the western horizon and the Alborz Mountains in Iran after sunset on December 17. The celestial gathering makes it easy to see Jupiter and fainter Saturn are separated on that date by roughly the diameter of the waxing crescent Moon. On the day of their Great Conjunction, solstice day December 21, Jupiter and Saturn may seem to nearly merge though. In their closest conjunction in 400 years they will be separated on the sky by only about 1/5 the apparent diameter of the Moon. By then the two largest worlds in the Solar System and their moons will be sharing the same field of view in telescopes around planet Earth.

ASTRONOMY - Diamond in the sky

 2020 December 18

Diamond in the Sky
Image Credit & Copyright: Mariano Ribas (Planetario de la Ciudad de Buenos Aires)

Explanation: When the shadow of the Moon raced across planet Earth's southern hemisphere on December 14, sky watchers along the shadow's dark central path were treated to the only total solar eclipse of 2020. During the New Moon's shadow play this glistening diamond ring was seen for a moment, even in cloudy skies. Known as the diamond ring effect, the transient spectacle actually happens twice. Just before and immediately after totality, a thin sliver of solar disk visible behind the Moon's edge creates the appearance of a shiny jewel set in a dark ring. This dramatic snapshot from the path of totality in northern Patagonia, Argentina captures this eclipse's second diamond ring, along with striking solar prominences lofted beyond the edge of the Moon's silhoutte.

ASTRONOMY - Gemini's Meteors

 2020 December 17

Gemini's Meteors
Image Credit & Copyright: Stefano Pellegrini

Explanation: Taken over the course of an hour shortly after local midnight on December 13, 35 exposures were used to create this postcard from Earth. The composited night scene spans dark skies above the snowy Italian Dolomites during our fair planet's annual Geminid meteor shower. Sirius, alpha star of Canis Major and the brightest star in the night, is grazed by a meteor streak on the right. The Praesepe star cluster, also known as M44 or the Beehive cluster, itself contains about a thousand stars but appears as a smudge of light far above the southern alpine peaks near the top. The shower's radiant is off the top of the frame though, near Castor and Pollux the twin stars of Gemini. The radiant effect is due to perspective as the parallel meteor tracks appear to converge in the distance. As Earth sweeps through the dust trail of asteroid 3200 Phaethon, the dust that creates Gemini's meteors enters Earth's atmosphere traveling at about 22 kilometers per second.