AERONAUTQUE - Avions de légende - Mistubishi A6M - Le "zéro"

Chasseur-bombardier monoplace japonais, le Mistubishi A6M a été à partir de 1939 et a joué un grand rôle durant la guerre contre les États-Unis. Redouté des pilotes américains, ce puissant monomoteur à hélice (plus de 900 chevaux) est assez caractéristique des chasseurs de la seconde guerre mondiale.

Le « Zero » (pour les Japonais), ou « Zeke » (pour les alliés), avait l'avantage d'une maniabilité exceptionnelle et d'une grande légèreté, lui garantissant une vitesse élevée (près de 600 km/h). Sa supériorité s'est cependant émoussée avec l'arrivée d'appareils américains beaucoup plus puissants (le P47 dépassait les 2.000 chevaux) et nombreux. Vulnérable car dépourvu de blindage afin de gagner du poids, il a fini par subir de lourdes pertes.

Les Zeros en état de vol sont aujourd'hui extrêmement rares et toujours le résultat d'une reconstruction. Celui qui peut être admiré chaque année au meeting de La Ferté-Alais, près de Paris, est en fait un North American T6 modifié, qui fut utilisé dans plusieurs films de cinéma.

© Paul Richter, Wikimedia commons, CC by-sa 3.0

ASTRONOMY - Comet Leonard and the Whale Galaxy

 2021 December 3

Comet Leonard and the Whale Galaxy
Image Credit & Copyright: Gregg Ruppel

Explanation: Sweeping through northern predawn skies, on November 24 Comet Leonard (C/2021 A1) was caught between two galaxies in this composite telescopic image. Sporting a greenish coma the comet's dusty tail seems to harpoon the heart of NGC 4631 (top) also known as the Whale Galaxy. Of course NGC 4631 and NGC 4656 (bottom, aka the Hockey Stick) are background galaxies some 25 million light-years away. On that date the comet was about 6 light-minutes from our fair planet. Its closest approach to Earth (and even closer approach to Venus) still to come, Comet Leonard will grow brighter in December. Already a good object for binoculars and small telescopes, this comet will likely not return to the inner Solar System. Its perihelion, or closest approach to the Sun, will be on January 3, 2022.

AERONAUTIQUE - Avions de légende - DC3/C47

 

À partir de 1936, le DC3, avec ses ailes basses « cantilever » (sans mâts ni haubans) portant deux moteurs, son fuselage cylindrique et son aérodynamisme, devient l'archétype de l'avion de ligne moderne. D'autres appareils lui ressemblent (comme le Boeing 247) mais c'est lui qui se vend le mieux. Il est rapide (plus de 300 km/h), fiable et confortable, avec un rayon d'action de plus de deux mille kilomètres.

Durant la seconde guerre mondiale, l'armée de l'air US le choisit comme avion de transport. Il devient le C47 (et le « Dakota » au Royaume-Uni), utilisé notamment pour les parachutages et le remorquage de planeurs. Décoré de bandes noires et blanches, il demeure un des symboles du débarquement des forces alliées en juin 1944.

Après la guerre, le DC3 connaît une carrière d'avion de ligne d'une invraisemblable durée. Dans les années 1960, à l'heure où apparaissent les jets, il équipe notamment Air France comme moyen-courrier. Aujourd'hui encore, équipé de turbines remplaçant les moteurs à pistons, il vole dans quelques endroits du monde.

L'appareil en photographie appartient à l'association France DC3, qui le produit en meeting aérien, comme ici à La Ferté Alais en mai 2009.

Futura Sciences

 2021 December 2

NGC 6822: Barnard's Galaxy
Image Credit & Copyright: Dietmar Hager, Eric Benson

Explanation: Grand spiral galaxies often seem to get all the glory, flaunting their young, bright, blue star clusters in beautiful, symmetric spiral arms. But small galaxies form stars too, like nearby NGC 6822, also known as Barnard's Galaxy. Beyond the rich starfields in the constellation Sagittarius, NGC 6822 is a mere 1.5 million light-years away, a member of our Local Group of galaxies. A dwarf irregular galaxy similar to the Small Magellanic Cloud, NGC 6822 is about 7,000 light-years across. Brighter foreground stars in our Milky Way have a spiky appearance. Behind them, Barnard's Galaxy is seen to be filled with young blue stars and mottled with the telltale pinkish hydrogen glow of star forming regions in this deep color composite image.

ASTRONOMY - A Blue-Banded Blood Moon

 2021 December 1

A Blue-Banded Blood Moon
Image Credit: Angel Yu

Explanation: What causes a blue band to cross the Moon during a lunar eclipse? The blue band is real but usually quite hard to see. The featured HDR image of last week's lunar eclipse, however -- taken from Yancheng, China -- has been digitally processed to equalize the Moon's brightness and exaggerate the colors. The gray color of the bottom right is the Moon's natural color, directly illuminated by sunlight. The upper left part of the Moon is not directly lit by the Sun since it is being eclipsed -- it in the Earth's shadow. It is faintly lit, though, by sunlight that has passed deep through Earth's atmosphere. This part of the Moon is red -- and called a blood Moon -- for the same reason that Earth's sunsets are red: because air scatters away more blue light than red. The unusual blue band is different -- its color is created by sunlight that has passed high through Earth's atmosphere, where red light is better absorbed by ozone than blue. A total eclipse of the Sun will occur tomorrow but, unfortunately, totality be visible only near the Earth's South Pole.

ASTRONOMY - The Extraordinary Spiral in LL Pegasi

 2021 November 29

The Extraordinary Spiral in LL Pegasi
Image Credit: NASA, ESA, Hubble, HLA; Processing & Copyright: Jonathan Lodge

Explanation: What created the strange spiral structure on the upper left? No one is sure, although it is likely related to a star in a binary star system entering the planetary nebula phase, when its outer atmosphere is ejected. The huge spiral spans about a third of a light year across and, winding four or five complete turns, has a regularity that is without precedent. Given the expansion rate of the spiral gas, a new layer must appear about every 800 years, a close match to the time it takes for the two stars to orbit each other. The star system that created it is most commonly known as LL Pegasi, but also AFGL 3068 and IRAS 23166+1655. The featured image was taken in near-infrared light by the Hubble Space Telescope. Why the spiral glows is itself a mystery, with a leading hypothesis being illumination by light reflected from nearby stars.

ASTRONOMY - A High Cliff on Comet Churyumov-Gerasimenko

 2021 November 28

A High Cliff on Comet Churyumov-Gerasimenko
Image Credit & Licence: ESA, Rosetta spacecraft, NAVCAM; Additional Processing: Stuart Atkinson

Explanation: This high cliff occurs not on a planet, not on a moon, but on a comet. It was discovered to be part of the dark nucleus of Comet Churyumov-Gerasimenko (CG) by Rosetta, a robotic spacecraft launched by ESA that rendezvoused with the Sun-orbiting comet in 2014. The ragged cliff, as featured here, was imaged by Rosetta in 2014. Although towering about one kilometer high, the low surface gravity of Comet CG would likely make it an accessible climb -- and even a jump from the cliff survivable. At the foot of the cliff is relatively smooth terrain dotted with boulders as large as 20 meters across. Data from Rosetta indicates that the ice in Comet CG has a significantly different deuterium fraction -- and hence likely a different origin -- than the water in Earth's oceans. Rosetta ended its mission with a controlled impact onto Comet CG in 2016. Comet CG has just completed another close approach to Earth and remains visible through a small telescope.

ASTRONOMY - Messier 101

 2021 November 27

Messier 101
Image Credit: NASA, ESA, CFHT, NOAO;
Acknowledgement - K.Kuntz (GSFC), F.Bresolin (U.Hawaii), J.Trauger (JPL), J.Mould (NOAO), Y.-H.Chu (U. Illinois)

Explanation: Big, beautiful spiral galaxy M101 is one of the last entries in Charles Messier's famous catalog, but definitely not one of the least. About 170,000 light-years across, this galaxy is enormous, almost twice the size of our own Milky Way. M101 was also one of the original spiral nebulae observed by Lord Rosse's large 19th century telescope, the Leviathan of Parsontown. Assembled from 51 exposures recorded by the Hubble Space Telescope in the 20th and 21st centuries, with additional data from ground based telescopes, this mosaic spans about 40,000 light-years across the central region of M101 in one of the highest definition spiral galaxy portraits ever released from Hubble. The sharp image shows stunning features of the galaxy's face-on disk of stars and dust along with background galaxies, some visible right through M101 itself. Also known as the Pinwheel Galaxy, M101 lies within the boundaries of the northern constellation Ursa Major, about 25 million light-years away.

MUSIC - J. S. Bach - "Air" Orchestral Suite N° 3 in D Major

"Orchestral Suite N° 3 in D Major"

ASTRONOMY - Great Refractor and Lunar Eclipse

 2021 November 26

Great Refractor and Lunar Eclipse
Image Credit & Copyright: Laurie Hatch

Explanation: Rain clouds passed and the dome of the Lick Observatory's 36 inch Great Refractor opened on November 19. The historic telescope was pointed toward a partially eclipsed Moon. Illuminated by dim red lighting to preserve an astronomer's night vision, telescope controls, coordinate dials, and the refractor's 57 foot long barrel were captured in this high dynamic range image. Visible beyond the foreshortened barrel and dome slit, growing brighter after its almost total eclipse phase, the lunar disk created a colorful halo through lingering clouds. From the open dome, the view of the clearing sky above includes the Pleiades star cluster about 5 degrees from Moon and Earth's shadow.