ASTRONOMY - Dark Nebulae and Star Formation in Taurus

 2023 March 21

Dark Nebulae and Star Formation in Taurus
Image Credit & Copyright: Vikas Chander

Explanation: Can dust be beautiful? Yes, and it can also be useful. The Taurus molecular cloud has several bright stars, but it is the dark dust that really draws attention. The pervasive dust has waves and ripples and makes picturesque dust bunnies, but perhaps more importantly, it marks regions where interstellar gas is dense enough to gravitationally contract to form stars. In the image center is a light cloud lit by neighboring stars that is home not only to a famous nebula, but to a very young and massive famous star. Both the star, T Tauri, and the nebula, Hind's Variable Nebula, are seen to vary dramatically in brightness -- but not necessarily at the same time, adding to the mystery of this intriguing region. T Tauri and similar stars are now generally recognized to be Sun-like stars that are less than a few million years old and so still in the early stages of formation. The featured image spans about four degrees not far from the Pleiades star cluster, while the featured dust field lies about 400 light-years away.

ASTRONOMY - M1: The Expanding Crab Nebula

 2023 March 20

M1: The Expanding Crab Nebula
Video Credit & Copyright: Detlef Hartmann

Explanation: Are your eyes good enough to see the Crab Nebula expand? The Crab Nebula is cataloged as M1, the first on Charles Messier's famous list of things which are not comets. In fact, the Crab is now known to be a supernova remnant, an expanding cloud of debris from the explosion of a massive star. The violent birth of the Crab was witnessed by astronomers in the year 1054. Roughly 10 light-years across today, the nebula is still expanding at a rate of over 1,000 kilometers per second. Over the past decade, its expansion has been documented in this stunning time-lapse movie. In each year from 2008 to 2022, an image was produced with the same telescope and camera from a remote observatory in Austria. The sharp, processed frames even reveal the dynamic energetic emission surrounding the rapidly spinning pulsar at the center. The Crab Nebula lies about 6,500 light-years away toward the constellation of the Bull (Taurus).

ASTRONOMY - Equinox at the Pyramid of the Feathered Serpent

 2023 March 19

Equinox at the Pyramid of the Feathered Serpent
Image Credit & Copyright: Robert Fedez

Explanation: To see the feathered serpent descend the Mayan pyramid requires exquisite timing. You must visit El Castillo -- in Mexico's Yucatán Peninsula -- near an equinox. Then, during the late afternoon if the sky is clear, the pyramid's own shadows create triangles that merge into the famous illusion of a slithering viper. Also known as the Temple of Kukulkan, the impressive step-pyramid stands 30 meters tall and 55 meters wide at the base. Built up as a series of square terraces by the pre-Columbian civilization between the 9th and 12th century, the structure can be used as a calendar and is noted for astronomical alignments. The featured composite image was captured in 2019 with Jupiter and Saturn straddling the diagonal central band of our Milky Way galaxy. Tomorrow marks another equinox -- not only at Temple of Kukulcán, but all over planet Earth.

ASTRONOMIE - Vénus flirte avec le fin croissant de Lune au crépuscule

 Cette attrayante rencontre est à admirer tout au long de la soirée du 24 mars 2023.

Positions de la Lune, de Vénus et de Jupiter vers 19h30 (heure de Paris) le 24 mars 2023. Le cercle bleu a un champ de six degrés typique d’une paire de jumelles 10×50.

Elle est désormais bien installée dans le ciel du soir, vers l’ouest : Vénus surpasse tous les astres alentours avec son éclat intense. Dans la soirée du 24 mars, la planète connue aussi sous le nom d’étoile du Berger doit pourtant partager la vedette avec la Lune. Avec son fin croissant âgé d’environ trois jours et sa lumière cendrée, notre satellite est aussi très attrayant.

Et c’est un régal pour les yeux de se tourner vers l’ouest à partir de 19h30 (heure de Paris) ! Vénus et la Lune sont éloignés d’un peu plus de trois degrés, une proximité qui les rend aussi observables ensemble dans une paire de jumelles classique. Vers 19h30 justement et si votre horizon est parfaitement dégagé, recherchez également la planète Jupiter, au ras de l’horizon. Mais cette dernière disparaît bien vite, laissant le champ libre à nos deux vedettes qui resplendissent de plus en plus à mesure que le ciel s’assombrit. Si vous ne pouvez pas quitter des yeux ce magnifique duo qui s’abaisse progressivement, sachez que vous pourrez en profiter jusqu’aux environs de 22h30 !

Stelvision

ASTRONOMY - The Medusa Nebula

 023 March 17

The Medusa Nebula
Image Credit & Copyright: Martin Bradley Chesterfield Astronomical Society

Explanation: Braided and serpentine filaments of glowing gas suggest this nebula's popular name, The Medusa Nebula. Also known as Abell 21, this Medusa is an old planetary nebula some 1,500 light-years away in the constellation Gemini. Like its mythological namesake, the nebula is associated with a dramatic transformation. The planetary nebula phase represents a final stage in the evolution of low mass stars like the sun as they transform themselves from red giants to hot white dwarf stars and in the process shrug off their outer layers. Ultraviolet radiation from the hot star powers the nebular glow. The Medusa's transforming star is the faint one near the center of the overall bright crescent shape. In this deep telescopic view, fainter filaments clearly extend below and right of the bright crescent region. The Medusa Nebula is estimated to be over 4 light-years across.

ASTRONOMY - Saturn's Hyperion: A Moon with Odd Craters

 2023 March 12

Saturn's Hyperion: A Moon with Odd Craters
Image Credit: NASA, ESA, JPL, SSI, Cassini Imaging Team

Explanation: What lies at the bottom of Hyperion's strange craters? To help find out, the robot Cassini spacecraft that once orbited Saturn swooped past the sponge-textured moon and took images of unprecedented detail. A six-image mosaic from the 2005 pass, featured here in scientifically assigned colors, shows a remarkable world strewn with strange craters and an odd, sponge-like surface. At the bottom of most craters lies some type of unknown dark reddish material. This material appears similar to that covering part of another of Saturn's moons, Iapetus, and might sink into the ice moon as it better absorbs warming sunlight. Hyperion is about 250 kilometers across, rotates chaotically, and has a density so low that it likely houses a vast system of caverns inside.

ASTRONOMY - Rainbow Tree

 2023 March 13

Rainbow Tree
Image Credit & Copyright: Eric Houck

Explanation: What lies at the end of a rainbow? Something different for everyone. For the photographer taking this picture, for example, one end of the rainbow ended at a tree. Others nearby, though, would likely see the rainbow end somewhere else. The reason is because a rainbow's position depends on the observer. The center of a rainbow always appears in the direction opposite the Sun, but that direction lines up differently on the horizon from different locations. This rainbow's arc indicates that its center is about 40 degrees to the left and slightly below the horizon, while the Sun is well behind the camera and just above the horizon. Reflections and refractions of sunlight from raindrops in a distant storm in the direction of the rainbow are what causes the colorful bands of light. This single exposure image was captured in early January near Knight's Ferry, California, USA.

PALEONTOLOGIE - Le hynéria - Un monstre sous-marin

Des paléontologues sud-africains ont dévoilé la découverte d’un fossile d’une nouvelle espèce de poisson préhistorique de genre Hyneria.

Quand on pense aux eaux profondes et à leurs prédateurs, on pense généralement aux requins. Seulement voilà, 95% des océans n’ont pas encore été exploités par l’Homme alors qui sait ce qui se cache encore dans les abysses.

Si les requins trônent évidemment en haut de la chaîne alimentaire aquatique, ils font pâle figure face à leurs ancêtres et d’autres monstres marins préhistoriques.

En effet, la science a mis au jour la diversité de super prédateurs aquatiques qui vivaient durant la préhistoire, à l’image du megalodon.

Mais c’est une autre espèce de poisson prédateur qui nous intéresse aujourd’hui avec la découverte révélée par des paléontologues sud-africains. En effet, des chercheurs de l’université Rhodes en Afrique du Sud ont découvert le fossile d’une nouvelle espèce de poisson préhistorique de genre Hyneria.

Le Hyneria, grand rival préhistorique du requin

Ces prédateurs marins étaient dotés d’immenses dents acérées. Dans leur étude, publiée dans la revue PLOS, ils ont identifié cette nouvelle espèce, appelée Hyneria Udlezinye, à partir d’un assemblage de plusieurs fossiles issus de Waterloo Farm, une région riche en fossiles dans la province du Cap, en Afrique du Sud.

Selon eux, ce prédateur préhistorique pouvait mesurer entre deux mètres cinquante et trois mètres soixante-dix et possédait des “crocs exceptionnellement grands” au niveau de sa mâchoire inférieure.Le Hyneria Udlezinye possédait “une bouche contenant des rangées de petites dents, mais aussi une paire de grands crocs qui pouvaient probablement atteindre cinq centimètres chez les plus grands spécimens”.

Cette espèce de poisson vivait dans les océans à l’époque du Dévonien tardif, il y a environ 383 à 359 millions d’années. Il était un féroce concurrent au requin, présent sur Terre depuis 430 millions d’années.

Demotivateur

ASTRONOMY - Orion and the Running Man

 2023 March 10

Orion and the Running Man
Image Credit & Copyright: Abraham Jones

Explanation: Few cosmic vistas excite the imagination like The Great Nebula in Orion. Visible as a faint celestial smudge to the naked-eye, the nearest large star-forming region sprawls across this sharp telescopic image, recorded on a cold January night in dark skies from West Virginia, planet Earth. Also known as M42, the Orion Nebula's glowing gas surrounds hot, young stars. About 40 light-years across, it lies at the edge of an immense interstellar molecular cloud only 1,500 light-years away within the same spiral arm of our Milky Way galaxy as the Sun. Along with dusty bluish reflection nebula NGC 1977 and friends near the top of the frame, the eye-catching nebulae represent only a small fraction of our galactic neighborhood's wealth of star-forming material. Within the well-studied stellar nursery, astronomers have also identified what appear to be numerous infant solar systems.

ASTRONOMY - DART vs Dimorphos

 023 March 9

DART vs Dimorphos
Image Credit: NASA, Johns Hopkins APL, DART

Explanation: On the first planetary defense test mission from planet Earth, the DART spacecraft captured this close-up on 26 September 2022, three seconds before slamming into the surface of asteroid moonlet Dimorphos. The spacecraft's outline with two long solar panels is traced at its projected point of impact between two boulders. The larger boulder is about 6.5 meters across. While the DART (Double Asteroid Redirection Test) spacecraft had a mass of some 570 kilograms, the estimated mass of Dimorphos, the smaller member of a near-Earth binary asteroid system, was about 5 billion kilograms. The direct kinetic impact of the spacecraft measurably altered the speed of Dimorphos by a fraction of a percent, reducing its 12 hour orbital period around its larger companion asteroid 65803 Didymos by about 33 minutes. Beyond successfully demonstrating a technique to change an asteroid's orbit that can prevent future asteroid strikes on planet Earth, the planetary-scale impact experiment has given the 150-meter-sized Dimorphos a comet-like tail of material.