GEMMOLOGIE - JOAILLERIE CELESTE (ET SPACIALE) - Instant T, une comète nommée 1P/Halley

1705, en pleine révolution scientifique, Edmond Halley – astronome et ingénieur anglais – publie un ouvrage qui fera date dans l’histoire de l’astronomie : A Synopsis of the Astronomy of Comets. Lui qui étudie le ciel depuis les années 1670 se passionne pour les étoiles. Après des études au Queen’s College d’Oxford, il navigue et catalogue les étoiles de l’hémisphère Sud, il sera aussi à l’origine de la découverte de la constellation du Centaure en 1677 quand il reprend les travaux de Ptolémée et de Johann Bayer. Dans son livre de 1705, il interroge le passage d’une comète en 1456, 1531, 1607 et 1682 et émet l’hypothèse qu’il s’agit de la même comète qui réapparait dans le ciel tous les 76 ans. Il prédit alors son retour en 1758 en basant sa théorie sur l’orbite elliptique et la durée estimée pour accomplir une révolution complète autour du soleil. Halley décède en 1742 et ne verra donc pas la vérification de ses prédictions. Il faut attendre 1757 pour que Joseph Jérôme Lefrançois de Lalande reprenne les calculs de Halley et ajuste la date du passage de la comète. En s’appuyant sur les possibles déviations de celle-ci dues à la présence de planètes, il annonce alors un retard à cause de Jupiter et de Saturne et affine le passage de la comète pour début 1759. Quand la comète apparait en décembre 1758 avec un périhélie (Le périhélie est le point de la trajectoire d’un objet céleste en orbite héliocentrique qui est le plus proche du Soleil) le 13 mars 1759, c’est un triomphe absolu. Et cela assoit définitivement la mécanique newtonienne en France. Ce passage permet de certifier les calculs de Halley qui voit la comète être baptisée en son nom.

LeGemmologue

ASTRONOMY - Little Planet Aurora

 2023 November 25

Little Planet Aurora
Image Credit & Copyright: Victor Lima

Explanation: Immersed in an eerie greenish light, this rugged little planet appears to be home to stunning water falls and an impossibly tall mountain. It's planet Earth of course. On the night of November 9 the nadir-centered 360 degree mosaic was captured by digital camera from the Kirkjufell mountain area of western Iceland. Curtains of shimmering Aurora Borealis or Northern Lights provide the pale greenish illumination. The intense auroral display was caused by solar activity that rocked Earth's magnetosphere in early November and produced strong geomagnetic storms. Kirkjufell mountain itself stands at the top of the stereographic projection's circular horizon. Northern hemisphere skygazers will recognize the familiar stars of the Big Dipper just above Kirkjufell's peak. At lower right the compact Pleiades star cluster and truly giant planet Jupiter also shine in this little planet's night sky.

ASTRONOMY - Stereo Jupiter near Opposition

 2023 November 24

Stereo Jupiter near Opposition
Image Credit & Copyright: Marco Lorenzi

Explanation: Jupiter looks sharp in these two rooftop telescope images. Both were captured on November 17 from Singapore, planet Earth, about two weeks after Jupiter's 2023 opposition. Climbing high in midnight skies the giant planet was a mere 33.4 light-minutes from Singapore. That's about 4 astronomical units away. Jupiter's planet girdling dark belts and light zones are visible in remarkable detail, along with the giant world's whitish oval vortices. Its signature Great Red Spot is still prominent in the south. Jupiter rotates rapidly on its axis once every 10 hours. So, based on video frames taken only 15 minutes apart, these images form a stereo pair. Look at the center of the pair and cross your eyes until the separate images come together to see the Solar System's ruling gas giant in 3D.

MACROPHOTOGRAPHIE - D’incroyables créations de la nature

Lorsque la neige tombe, certains sont agacés. Ils pensent aux difficultés qu’ils vont avoir à se déplacer ou à la neige qu’il faudra bientôt déblayer sur le trottoir. D’autres sont émerveillés. Mais, même ceux-là n’imaginent probablement pas quelles incroyablement belles créations de la nature se cachent au milieu de ces flocons à l’apparence duveteuse.

Et le flocon que le photographe russe Alexey Kjatov a immortalisé ici en est un incroyable exemple. Une photo qui lui a demandé un important travail de mise en forme pour un flocon à 12 branches d’environ 5 millimètres de diamètre.

© Olga & Alexey, Flickr, CC by-nc 2.0

FuturaSciences

ASTRONOMY - Along the Taurus Molecular Cloud

 2023 November 23

Along the Taurus Molecular Cloud
Image Credit & Copyright: Yuexiao Shen, Joe Hua

Explanation: The cosmic brush of star formation composed this interstellar canvas of emission, dust, and dark nebulae. A 5 degree wide telescopic mosaic, it frames a region found north of bright star Aldebaran on the sky, at an inner wall of the local bubble along the Taurus molecular cloud. At lower left, emission cataloged as Sh2-239 shows signs of embedded young stellar objects. The region's Herbig-Haro objects, nebulosities associated with newly born stars, are marked by tell-tale reddish jets of shocked hydrogen gas. Above and right T Tauri, the prototype of the class of T Tauri variable stars, is next to a yellowish nebula historically known as Hind's Variable Nebula (NGC 1555). T Tauri stars are now generally recognized as young, less than a few million years old, sun-like stars still in the early stages of formation.

ASTRONOMY - IC 342: Hidden Galaxy in Camelopardalis

 2023 November 22

IC 342: Hidden Galaxy in Camelopardalis
Image Credit & Copyright: Steve Cannistra

Explanation: Similar in size to large, bright spiral galaxies in our neighborhood, IC 342 is a mere 10 million light-years distant in the long-necked, northern constellation Camelopardalis. A sprawling island universe, IC 342 would otherwise be a prominent galaxy in our night sky, but it is hidden from clear view and only glimpsed through the veil of stars, gas and dust clouds along the plane of our own Milky Way galaxy. Even though IC 342's light is dimmed and reddened by intervening cosmic clouds, this sharp telescopic image traces the galaxy's own obscuring dust, young star clusters, and glowing star forming regions along spiral arms that wind far from the galaxy's core. IC 342 has undergone a recent burst of star formation activity and is close enough to have gravitationally influenced the evolution of the local group of galaxies and the Milky Way.

ASTRONOMY - Fleming's Triangular Wisp

 2023 November 21

Fleming's Triangular Wisp
Image Credit & Copyright: Cristiano Gualco

Explanation: These chaotic and tangled filaments of shocked, glowing gas are spread across planet Earth's sky toward the constellation of Cygnus as part of the Veil Nebula. The Veil Nebula itself is a large supernova remnant, an expanding cloud born of the death explosion of a massive star. Light from the original supernova explosion likely reached Earth over 5,000 years ago. The glowing filaments are really more like long ripples in a sheet seen almost edge on, remarkably well separated into the glow of ionized hydrogen atoms shown in red and oxygen in blue hues. Also known as the Cygnus Loop and cataloged as NGC 6979, the Veil Nebula now spans about 6 times the diameter of the full Moon. The length of the wisp corresponds to about 30 light years, given its estimated distance of 2,400 light years. Often identified as Pickering's Triangle for a director of Harvard College Observatory, it is perhaps better named for its discoverer, astronomer Williamina Fleming, as Fleming's Triangular Wisp.

ASTRONOMY - The Horsehead Nebula

 2023 November 20

The Horsehead Nebula
Image Credit & Copyright: Mark Hanson & Martin Pugh, SSRO, PROMPT, CTIO, NSF

Explanation: Sculpted by stellar winds and radiation, a magnificent interstellar dust cloud by chance has assumed this recognizable shape. Fittingly named the Horsehead Nebula, it is some 1,500 light-years distant, embedded in the vast Orion cloud complex. About five light-years "tall," the dark cloud is cataloged as Barnard 33 and is visible only because its obscuring dust is silhouetted against the glowing red emission nebula IC 434. Stars are forming within the dark cloud. Contrasting blue reflection nebula NGC 2023, surrounding a hot, young star, is at the lower left of the full image. The featured gorgeous color image combines both narrowband and broadband images recorded using several different telescopes.

ASTRONOMY - Space Station, Solar Prominences, Sun

 2023 November 19

Space Station, Solar Prominences, Sun
Image Credit & Copyright: Mehmet Ergün

Explanation: That's no sunspot. It's the International Space Station (ISS) caught passing in front of the Sun. Sunspots, individually, have a dark central umbra, a lighter surrounding penumbra, and no Dragon capsules attached. By contrast, the ISS is a complex and multi-spired mechanism, one of the largest and most complicated spacecraft ever created by humanity. Also, sunspots circle the Sun, whereas the ISS orbits the Earth. Transiting the Sun is not very unusual for the ISS, which orbits the Earth about every 90 minutes, but getting one's location, timing and equipment just right for a great image is rare. The featured picture combined three images all taken in 2021 from the same location and at nearly the same time. One image -- overexposed -- captured the faint prominences seen across the top of the Sun, a second image -- underexposed -- captured the complex texture of the Sun's chromosphere, while the third image -- the hardest to get -- captured the space station as it shot across the Sun in a fraction of a second. Close inspection of the space station's silhouette even reveals a docked Dragon Crew capsule.

ASTRONOMY - Planet Earth from Orion

 2023 November 18

Planet Earth from Orion
Image Credit: NASA, Artemis I

Explanation: One year ago a Space Launch System rocket left planet Earth on November 16, 2022 at 1:47am EST carrying the Orion spacecraft on the Artemis I mission, the first integrated test of NASA’s deep space exploration systems. Over an hour after liftoff from Kennedy Space Center's historic Launch Complex 39B, one of Orion's external video cameras captured this view of its new perspective from space. In the foreground are Orion's Orbital Maneuvering System engine and auxillary engines, at the bottom of the European Service Module. Beyond one of the module's 7-meter long extended solar array wings lies the spacecraft's beautiful home world. Making close flybys of the lunar surface and reaching a retrograde orbit 70,000 kilometers beyond the Moon, the uncrewed Artemis I mission lasted over 25 days, testing capabilities to enable human exploration of the Moon and Mars. Building on the success of Artemis I, no earlier than November 2024 the Artemis II mission with a crew of 4 will venture around the Moon and back again.