ASTRONOMY - Swiss Alps, Martian Sky

 2021 February 18

Swiss Alps, Martian Sky
Image Credit & Copyright: Jens Bydal

Explanation: Taken on February 6, this snowy mountain and skyscape was captured near Melchsee-Frutt, central Switzerland, planet Earth. The reddish daylight and blue tinted glow around the afternoon Sun are colors of the Martian sky, though. Of course both worlds have the same Sun. From Mars, the Sun looks only about half as bright and 2/3 the size compared to its appearance from Earth. Lofted from the surface of Mars, fine dust particles suspended in the thin Martian atmosphere are rich in the iron oxides that make the Red Planet red. They tend to absorb blue sunlight giving a red tinge to the Martian sky, while forward scattering still makes the light appear relatively bluish near the smaller, fainter Martian Sun. Normally Earth's denser atmosphere strongly scatters blue light, making the terrestrial sky blue. But on February 6 a huge cloud of dust blown across the Mediterranean from the Sahara desert reached the Swiss Alps, dimming the Sun and lending that Alpine afternoon the colors of the Martian sky. By the next day, only the snow was left covered with reddish dust.

ASTRONOMY - Sun Pillar with Upper Tangent Arc

 2021 February 17

Sun Pillar with Upper Tangent Arc
Image Credit & Copyright: Mike Cohea

Explanation: This was not a typical sun pillar. Just after sunrise two weeks ago in Providence, Rhode Island, USA, a photographer, looking out his window, was suddenly awestruck. The astonishment was caused by a sun pillar that fanned out at the top. Sun pillars, singular columns of light going up from the Sun, are themselves rare to see, and are known to be caused by sunlight reflecting from wobbling, hexagon-shaped ice-disks falling through Earth's atmosphere. Separately, upper tangent arcs are known to be caused by sunlight refracting through falling hexagon-shaped ice-tubes. Finding a sun pillar connected to an upper tangent arc is extraordinary, and, initially, took some analysis to figure out what was going on. A leading theory is that this sun pillar was also created, in a complex and unusual way, by falling ice tubes. Few might believe that such a rare phenomenon was seen again if it wasn't for the quick thinking of the photographer -- and the camera on his nearby smartphone.

ASTRONOMY - Landing on Mars: Seven Minutes of Terror

 2021 February 15

Landing on Mars: Seven Minutes of Terror
Video Credit: NASA, JPL

Explanation: Starting Thursday, there may be an amazing new robotic explorer on Mars. Or there may be a new pile of junk. It all likely depends on things going correctly in the minutes after the Mars 2020 mission arrives at its new home planet and attempts to deploy the Perseverance rover. Arguably the most sophisticated landing yet attempted on the red planet, consecutive precision events will involve a heat shield, a parachute, several rocket maneuvers, and the automatic operation of an unusual device called a Sky Crane. Thursday's Seven Minutes of Terror echo the landing of the Curiosity rover on Mars in 2012, as depicted in the featured video. If successful, the car-sized Perseverance rover will rest on the surface of Mars, soon to begin exploring Jezero Crater to better determine the habitability of this seemingly barren world to life -- past, present, and future. Although multiple media outlets may cover this event, one way to watch these landing events unfold is on the NASA channel live on the web.

ASTRONOMY - Firing Lasers to Tame the Sky

 2021 February 10

Firing Lasers to Tame the Sky
Image Credit & Copyright: Juan Carlos Muñoz / ESO; Text: Juan Carlos Muñoz

Explanation: Why do stars twinkle? Our atmosphere is to blame as pockets of slightly off-temperature air, in constant motion, distort the light paths from distant astronomical objects. Atmospheric turbulence is a problem for astronomers because it blurs the images of the sources they want to study. The telescope featured in this image, located at ESO’s Paranal Observatory, is equipped with four lasers to combat this turbulence. The lasers are tuned to a color that excites atoms floating high in Earth's atmosphere -- sodium left by passing meteors. These glowing sodium spots act as artificial stars whose twinkling is immediately recorded and passed to a flexible mirror that deforms hundreds of times per second, counteracting atmospheric turbulence and resulting in crisper images. The de-twinkling of stars is a developing field of technology and allows, in some cases, Hubble-class images to be taken from the ground. This technique has also led to spin-off applications in human vision science, where it is used to obtain very sharp images of the retina.

PRATIQUE - Une noix réparatrice de meubles

 

ASTRONOMY - Flashes of the Crab Pulsar

 2021 February 9

Flashes of the Crab Pulsar
Video Credit & Copyright: Martin Fiedler

Explanation: It somehow survived an explosion that would surely have destroyed our Sun. Now it is spins 30 times a second and is famous for the its rapid flashes. It is the Crab Pulsar, the rotating neutron star remnant of the supernova that created the Crab Nebula. A careful eye can spot the pulsar flashes in the featured time-lapse video, just above the image center. The video was created by adding together images taken only when the pulsar was flashing, as well as co-added images from other relative times. The Crab Pulsar flashes may have been first noted by an unknown woman attending a public observing night at the University of Chicago in 1957 -- but who was not believed. The progenitor supernova explosion was seen by many in the year 1054 AD. The expanding Crab Nebula remains a picturesque expanding gas cloud that glows across the electromagnetic spectrum. The pulsar is now thought to have survived the supernova explosion because it is composed of extremely-dense quantum-degenerate matter.

ASTRONOMY - WR32 and Interstellar Clouds in Carina

 2021 February 8

WR32 and Interstellar Clouds in Carina
Image Credit & Copyright: Ariel Cappelletti

Explanation: Stars can be like artists. With interstellar gas as a canvas, a massive and tumultuous Wolf-Rayet star has created the picturesque ruffled half-circular filaments called WR32, on the image left. Additionally, the winds and radiation from a small cluster of stars, NGC 3324, have sculpted a 35 light year cavity on the upper right, with its right side appearing as a recognizable face in profile. This region's popular name is the Gabriela Mistral Nebula for the famous Chilean poet. Together, these interstellar clouds lie about 8,000 light-years away in the Great Carina Nebula, a complex stellar neighborhood harboring numerous clouds of gas and dust rich with imagination inspiring shapes. The featured telescopic view captures these nebulae's characteristic emission from ionized sulfur, hydrogen, and oxygen atoms mapped to the red, green, and blue hues of the popular Hubble Palette.

ASTRONOMY - A Northern Winter Night

 2021 February 6

A Northern Winter Night
Image Credit & Copyright: Lukasz Zak

Explanation: Snow blankets the ground in this serene forest and sky view. Assembled in a 360 degree panoramic projection, the mosaicked frames were captured at January's end along a quiet country road near Siemiony, northeastern Poland, planet Earth. The night was cold and between trees reaching toward the sky shine the stars and nebulae of the northern winter Milky Way. Near zenith is bright star Capella, a mere 43 light-years above the tree tops. Alpha star of the constellation Auriga the Charioteer and part of the winter hexagon asterism, Capella is a well-studied double star system. Follow the Milky Way above and right of Capella and you might spot the familiar stars of Orion in the northern winter night.

AERONAUTIQUE - Avion du futur en 1944

Avez-vous déjà imaginé votre transport du futur ? C’est l’idée du magazine Popular Science qui a laissé à Douglas Rolfe tout le loisir de créer son avion personnel. Le résultat est plutôt réaliste et bluffant, ce qui peut s’expliquer par le fait qu'en 1944 l’aviation avait déjà fait un grand bon avec la première et la seconde guerre mondiale.

© Douglas Rolfe, juillet 1944, revue Popular Science

ASTRONOMY - A view from Antares

 2021 February 4

Apollo 14: A View from Antares
Image Credit: Edgar Mitchell, Apollo 14, NASA; Mosaic - Eric M. Jones

Explanation: Fifty years ago this Friday, Apollo 14's Lunar Module Antares landed on the Moon. Toward the end of the stay astronaut Ed Mitchell snapped a series of photos of the lunar surface while looking out a window, assembled into this detailed mosaic by Apollo Lunar Surface Journal editor Eric Jones. The view looks across the Fra Mauro highlands to the northwest of the landing site after the Apollo 14 astronauts had completed their second and final walk on the Moon. Prominent in the foreground is their Modular Equipment Transporter, a two-wheeled, rickshaw-like device used to carry tools and samples. Near the horizon at top center is a 1.5 meter wide boulder dubbed Turtle rock. In the shallow crater below Turtle rock is the long white handle of a sampling instrument, thrown there javelin-style by Mitchell. Mitchell's fellow moonwalker and first American in space, Alan Shepard, also used a makeshift six iron to hit two golf balls. One of Shepard's golf balls is just visible as a white spot below Mitchell's javelin.