Science & Technologie - Le monde des requins : Le requin-marteau : une bonne Tête avec un grand T

Reconnaissables à leur tête en forme de T, les requins-marteaux regroupent dix espèces de la famille des Sphyrnidés. Ils sont en général de taille modeste, mais le plus imposant d'entre eux, legrand requin marteau (Sphyrna mokarran), peut mesurer jusqu'à 6 mètres de long pour 450 kg. Ils évoluent en bancs le jour, puis se muent en loups solitaires la nuit pour chasser. Leur tête de marteau devient alors un outil très efficace. Ils bénéficient d'un champ de vision élargi, car leursyeux sont placés aux deux extrémités de ces protubérances, et peuvent clouer au sol les raies, pour lesquelles ils ont une petite préférence.

Certaines espèces de requins marteaux sont considérées comme vulnérables par l'UICN. D'autres sont classées en danger : c'est le cas du grand requin marteau.

© Martin, Fotolia

Science & Technology - Astronomy picture of the day : AZURE Vapor Tracers over Norway

2019 April 8
AZURE Vapor Tracers over Norway 
Image Credit & Copyright: Yang Sutie

Explanation: What's happening in the sky? The atmosphere over northern Norway appeared quite strange for about 30 minutes last Friday when colorful clouds, dots, and plumes suddenly appeared. The colors were actually created by the NASA-funded Auroral Zone Upwelling Rocket Experiment (AZURE) which dispersed gas tracers to probe winds in Earth's upper atmosphere. AZURE's tracers originated from two short-lived sounding rockets launched from the Andøya Space Center in Norway. The harmless gases, trimethylaluminum and a barium/strontium mixture, were released into the ionosphere at altitudes of 115 and 250 km. The vapor trails were observed dispersing from several ground stations. Mapping how AZURE's vapors dispersed should increase humanity's understanding of how the solar wind transfers energy to the Earth and powers aurora.

Science & Technology - Astronomy picture of the day : First Horizon-Scale Image of a Black Hole

2019 April 11
First Horizon-Scale Image of a Black Hole Image Credit: Event Horizon Telescope Collaboration

Explanation: What does a black hole look like? To find out, radio telescopes from around the Earth coordinated observations of black holes with the largest known event horizons on the sky. Alone, black holes are just black, but these monster attractors are known to be surrounded by glowing gas. The first image was released yesterday and resolved the area around the black hole at the center of galaxy M87 on a scale below that expected for its event horizon.Pictured, the dark central region is not the event horizon, but rather the black hole's shadow -- the central region of emitting gas darkened by the central black hole's gravity. The size and shape of the shadow is determined by bright gasnear the event horizon, by strong gravitational lensing deflections, and by the black hole's spin. In resolving this black hole's shadow, the Event Horizon Telescope (ETH) bolstered evidence that Einstein's gravity works even in extreme regions, and gave clear evidence that M87 has a central spinning black hole of about 6 billion solar masses. The EHT is not done -- future observations will be geared toward even higher resolution, better tracking of variability, and exploring the immediate vicinity of the black hole in the center of our Milky Way Galaxy.

Science & Technology - Astronomy picture of the day : A Scorpius Sky Spectacular

019 April 7
A Scorpius Sky Spectacular Image Credit & Copyright: Stéphane Guisard, TWAN

Explanation: If Scorpius looked this good to the unaided eye, humans might remember it better. Scorpius more typically appears as a few bright stars in a well-known but rarely pointed out zodiacal constellation. To get a spectacular image like this, though, one needs a good camera, color filters, and a digital image processor. To bring out detail, the featured image not only involved long duration exposures taken in several colors, but one exposure in a very specific red color emitted by hydrogen. The resulting image shows many breathtaking features. Vertically across the image left is part of the plane of our Milky Way Galaxy. Visible there are vast clouds of bright stars and long filaments of darkdust. Jutting out diagonally from the Milky Way in the image center are dark dust bands known as the Dark River. This river connects to several bright stars on the right that are part of Scorpius' head and claws, and include the bright star Antares. Above and right of Antares is an even brighter planet: Jupiter. Numerous red emission nebulas and blue reflection nebulas are visible throughout the image. Scorpius appears prominently in southern skies after sunset during the middle of the year.

Science & Technology - Astronomy picture of the day : Messier 2

2019 April 4
Messier 2 Image Credit: ESA/Hubble & NASA, G. Piotto et al.

Explanation: After the Crab Nebula, M1, this giant star cluster is the second entry in 18th century astronomer Charles Messier's famous list of things with are not comets. M2 is one of the largest globular star clusters now known to roam the halo of our Milky Way galaxy. Though Messier originally described it a nebula without stars, this stunning Hubble image resolves stars across the central 40 light-years of M2. Its population of stars numbers close to 150,000, concentrated within a total diameter of around 175 light-years. About 55,000 light-years distant toward the constellation Aquarius, this ancient denizen of the Milky Way, also known as NGC 7089, is 13 billion years old.

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Science & Technology - Astronomy picture of the day : Wisps Surrounding the Horsehead Nebula

2019 April 3
Wisps Surrounding the Horsehead Nebula 
Image Credit & Copyright: Mario Zauner

Explanation: The famous Horsehead Nebula in Orion is not alone. A deep exposure shows that the dark 

familiar shaped indentation, visible just below center, is part of a vast complex of absorbing dust and glowing gas. To bring out details of the Horsehead's pasture, an amateur astronomer used a backyard telescope in Austria to accumulate and artistically combine 7.5 hours of images in the light of Hydrogen (red), Oxygen (green), and Sulfur (blue). The resulting spectacular picture details an intricate tapestry of gaseous wisps and dust-laden filaments that were created and sculpted over eons by stellar winds and ancient supernovas. The Flame Nebula is visible just to the left of the Horsehead, while the bright star on the upper left is Alnilam, the central star in Orion's Belt. The Horsehead Nebula lies 1,500 light years distant towards the constellation of Orion.

Science & Technology - Astronomy picture of the day : Space Station Silhouette on the Moon

2019 April 2
Space Station Silhouette on the Moon 
Image Credit & Copyright: Eric Holland

Explanation: What's that unusual spot on the Moon? It's the International Space Station. Using precise timing, the Earth-orbiting space platform was photographed in front of a partially lit gibbous Moon last month. The featured image was taken from Palo Alto, California, USA with an exposure time of only 1/667 of a second. In contrast, the duration of the transit of the ISS across the entire Moon was about half a second. A close inspection of this unusually crisp ISS silhouette will reveal the outlines of numerous solar panels and trusses. The bright crater Tycho is visible on the lower left, as well as comparatively rough, light colored terrain known as highlands, and relatively smooth, dark colored areas known as maria. On-line tools can tell you when the International Space Station will be visible from your area.

Estatísticas - Visualizações deste blogue até 31-03-2019

USA, 5.913

FRANCE, 3.307

??? REGIÃO DESCONHECIDA, 1.402

ALEMANHA, 971

BRASIL, 921

BÉLGICA, 786

UCRÂNIA, 675

EMIRADOS ÁRABES UNIDOS, 547

CANADA, 408

RÚSSIA, 275

Science & Technology - Astronomy picture of the day : Astronaut Kicks Lunar Field Goal

2019 April 1
Astronaut Kicks Lunar Field Goal 

Image Credit: NASA, Apollo 15 Team

Explanation: Score three points for NASA. With time running out late in Apollo 15's mission to the Moon in 1971, Astronaut David Scott prepared to split the uprights and bring about yet another dramatic end-of-the-mission victory for NASA. Scott used a special lunar football designed for the rugged games held on the Moon. R1-D1, a predecessor to R2-D2, cheered from the sideline. Happy April Fools' Day from the folks at APOD. In reality, Astronaut Scottplaced a drill that measured how temperature changed with lunar depth. The foreground device actually detected high-energy particles that escaped from the Sun.