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22/07/2023

GEMMOLOGIE - La fluorine


La fluorine, ou fluorite, est composée de fluorure de calcium (CaF2). Elle possède également des traces de différents ions, ce qui explique ses multiples couleurs. Elle est souvent utilisée en astronomie afin de limiter les phénomènes d'aberration chromatique sur les lentilles et les objectifs. Couleurs : incolore, vert, rose, violet, bleu, etc. 

© Rob Lavinsky, Wikimedia Commons, CC by-sa 3.0

ART FRACTAL - Inquiétante image fractale sur fond rouge


Six petits bonshommes blancs se dirigent avec empressement vers le tapis rouge. Où vont-ils ? Le fond rouge monochrome sur lequel se dessinent des sortes de fissures blanche et verte en forme de flocons de neige ne semble pas très rassurant... 

© Futura

ASTRONOMY - Apollo 11: Armstrong's Lunar Selfie

 2023 July 22

See Explanation.  Clicking on the picture will download
the highest resolution version available.

Apollo 11: Armstrong's Lunar Selfie
Image Credit: NASAApollo 11Neil Armstrong; Processing: Michael Ranger

Explanation: A photograph of Buzz Aldrin standing on the Moon taken by Neil Armstrong, was digitally reversed to create this lunar selfie. Captured in July 1969 following the Apollo 11 moon landing, Armstrong's original photograph recorded not only the magnificent desolation of an unfamiliar world, but Armstrong himself reflected in Aldrin's curved visor. In the unwrapped image, the spherical distortion of the reflection in Aldrin's helmet has been reversed. The transformed view features Armstrong himself from Aldrin's perspective. Since Armstrong took the original picture, today the image represents a fifty-four year old lunar selfie. Aldrin's visor reflection in the original image appears here on the left. Bright (but distorted) planet Earth hangs in the lunar sky above Armstrong's figure, toward the upper right. A foil-wrapped leg of the Eagle lander and Aldrin's long shadow stretching across the lunar surface are prominently visible. In 2024 NASA's Artemis II mission will return humans to the Moon.

21/07/2023

ASTRONOMY - Meteor and Milky Way over the Alps

 2023 July 16

A person is seen facing away, standing on a peak. Other mountain peaks
surround them. City lights are seen in towns and along roads below. Stars
in the night sky are above. The band of the Milky Way galaxy slants down
from the upper left. A bright green meteor streak slants down from above.
Please see the explanation for more detailed information.

Meteor and Milky Way over the Alps
Image Credit & Copyright: Nicholas Roemmelt (Venture Photography)

Explanation: Now this was a view with a thrill. From Mount Tschirgant in the Alps, you can see not only nearby towns and distant Tyrolean peaks, but also, weather permitting, stars, nebulas, and the band of the Milky Way Galaxy. What made the arduous climb worthwhile this night, though, was another peak -- the peak of the 2018 Perseids Meteor Shower. As hoped, dispersing clouds allowed a picturesque sky-gazing session that included many faint meteors, all while a carefully positioned camera took a series of exposures. Suddenly, a thrilling meteor -- bright and colorful -- slashed down right next to the nearly vertical band of the Milky Way. As luck would have it, the camera caught it too. Therefore, a new image in the series was quickly taken with one of the sky-gazers posing on the nearby peak. Later, all of the images were digitally combined.

15/07/2023

ASTRONOMY - Webb's Rho Ophiuchi

 2023 July 13

See Explanation.  Clicking on the picture will download
the highest resolution version available.

Webb's Rho Ophiuchi
Image Credit: NASAESACSASTScI, Klaus Pontoppidan (STScI), Processing: Alyssa Pagan (STScI)

Explanation: A mere 390 light-years away, Sun-like stars and future planetary systems are forming in the Rho Ophiuchi molecular cloud complex, the closest star-forming region to our fair planet. The James Webb Space Telescope's NIRCam peered into the nearby natal chaos to capture this infrared image at an inspiring scale. The spectacular cosmic snapshot was released to celebrate the successful first year of Webb's exploration of the Universe. The frame spans less than a light-year across the Rho Ophiuchi region and contains about 50 young stars. Brighter stars clearly sport Webb's characteristic pattern of diffraction spikes. Huge jets of shocked molecular hydrogen blasting from newborn stars are red in the image, with the large, yellowish dusty cavity carved out by the energetic young star near its center. Near some stars in the stunning image are shadows cast by their protoplanetary disks.

10/07/2023

ASTRONOMY - Stars, Dust and Nebula in NGC 6559

 2023 July 10

A busy star formation region is shown highlighted by red glowing clouds
and dark ominously-shaped dust.
Please see the explanation for more detailed information.

Stars, Dust and Nebula in NGC 6559
Image Credit & Copyright: Adam BlockTelescope Live

Explanation: When stars form, pandemonium reigns. A textbook case is the star forming region NGC 6559. Visible in the featured image are red glowing emission nebulas of hydrogen, blue reflection nebulas of dust, dark absorption nebulas of dust, and the stars that formed from them. The first massive stars formed from the dense gas will emit energetic light and winds that erode, fragment, and sculpt their birthplace. And then they explode. The resulting morass can be as beautiful as it is complex. After tens of millions of years, the dust boils away, the gas gets swept away, and all that is left is a bare open cluster of stars.

09/07/2023

METEOROLOGIE - Phénomène extraordinaire : le nuage en forme de champignon atomique


Avez-vous déjà eu l'impression qu'une explosion nucléaire était en train de se produire dans le ciel ? Lors de plus fortes dégradations orageuses, il arrive parfois qu'un nuage en forme de champignon atomique surgisse dans le ciel.

Il s'agit d'un type particulier de nuage d'orage, le Cumulonimbus capillatus incus. Le cumulonimbus est en fait un terme général qui désigne tout nuage d'orage, mais il en existe plusieurs espèces avec des conséquences différentes. Les orages les plus impressionnants en forme de champignon atomique font souvent la Une des actualités des médias locaux. Il arrive même qu'ils créent des moments de panique parmi la population, tant leur forme peut être inquiétante.

Qu'est ce qui donne à un simple cumulonimbus une allure aussi apocalyptique ? C'est en réalité l'enclume très étendue qui donne cette impression de catastrophe nucléaire. L'enclume (incus en latin) est le sommet du nuage d'orage, qui s'étire horizontalement sur 20 à 50 kilomètres lorsqu'il arrive au niveau de la tropopause. Le nuage ne peut plus continuer de monter en altitude, son sommet s'écrase alors contre la tropopause et forme une sorte de couvercle.


FuturaSciences

ASTRONOMY - Doomed Star Eta Carinae

 2023 July 9

A Hubble image of the gas and dust surrounding the star Eta Carinae 
is shown. The nebula has two distinct light-colored lobes, surrounded by
red glowing gas. 
Please see the explanation for more detailed information.

Doomed Star Eta Carinae
Image Credit & Copyright: NASAESAHubbleProcessing & LicenseJudy Schmidt

Explanation: Eta Carinae may be about to explode. But no one knows when - it may be next year, it may be one million years from now. Eta Carinae's mass - about 100 times greater than our Sun - makes it an excellent candidate for a full blown supernova. Historical records do show that about 170 years ago Eta Carinae underwent an unusual outburst that made it one of the brightest stars in the southern skyEta Carinae, in the Keyhole Nebula, is the only star currently thought to emit natural LASER light. This featured image brings out details in the unusual nebula that surrounds this rogue starDiffraction spikes, caused by the telescope, are visible as bright multi-colored streaks emanating from Eta Carinae's center. Two distinct lobes of the Homunculus Nebula encompass the hot central region, while some strange radial streaks are visible in red extending toward the image right. The lobes are filled with lanes of gas and dust which absorb the blue and ultraviolet light emitted near the center. The streaks, however, remain unexplained.

06/07/2023

ASTRONOMY - Fireworks vs Supermoon

 2023 July 6

See Explanation.  Clicking on the picture will download
the highest resolution version available.

Fireworks vs Supermoon
Image Credit & CopyrightMichael Seeley

Explanation: On July 4, an almost Full Moon rose in planet Earth's evening skies. Also known as a Buck Moon, the full lunar phase (full on July 3 at 11:39 UTC) was near perigee, the closest point in the Moon's almost monthly orbit around planet Earth. That qualified this July's Full Moon as a supermoon, the first of four supermoons in 2023. Seen from Cocoa Beach along Florida's Space Coast on July 4, any big, bright, beautiful Full Moon would still have to compete for attention though. July's super-moonrise was captured here against a super-colorful fireworks display.

PHOTOGRAPHIE - Le monde explosif d'Alan Sailer - Au ralenti : explosion d'un litchi


Un litchi qui explose sous l'impact d'une balle de plomb très rapide qui se déplace à environ 200 mètres par seconde. Tirée à partir d'un fusil à plomb, la balle a une énergie totale d'environ 10 joules.


© Alan Sailer

ASTRONOMIE - Les quatre lunes galiléennes de Jupiter

Publiée en novembre 1997, cette image représente les quatre lunes galiléennes de Jupiter . De haut en bas, on peut apercevoir Io , Europe, ...