ASTRONOMY - Planet Earth at Twilight

 2021 April 22

Planet Earth at Twilight
Image Credit: ISS Expedition 2 Crew, Gateway to Astronaut Photography of Earth, NASA

Explanation: No sudden, sharp boundary marks the passage of day into night in this gorgeous view of ocean and clouds over our fair planet Earth. Instead, the shadow line or terminator is diffuse and shows the gradual transition to darkness we experience as twilight. With the Sun illuminating the scene from the right, the cloud tops reflect gently reddened sunlight filtered through the dusty troposphere, the lowest layer of the planet's nurturing atmosphere. A clear high altitude layer, visible along the dayside's upper edge, scatters blue sunlight and fades into the blackness of space. This picture was taken in June of 2001 from the International Space Station orbiting at an altitude of 211 nautical miles. But you can check out the vital signs of Planet Earth Now.

ASTRONOMY - Centaurus A's Warped Magnetic Fields

 2021 April 21

Centaurus A's Warped Magnetic Fields
Image Credit: Optical: European Southern Observatory (ESO) Wide Field Imager; Submillimeter: Max Planck Institute for Radio Astronomy/ESO/Atacama Pathfinder Experiment (APEX)/A.Weiss et al; X-ray and Infrared: NASA/Chandra/R. Kraft; JPL-Caltech/J. Keene; Text: Joan Schmelz (USRA)

Explanation: When galaxies collide -- what happens to their magnetic fields? To help find out, NASA pointed SOFIA, its flying 747, at galactic neighbor Centaurus A to observe the emission of polarized dust -- which traces magnetic fields. Cen A's unusual shape results from the clash of two galaxies with jets powered by gas accreting onto a central supermassive black hole. In the resulting featured image, SOFIA-derived magnetic streamlines are superposed on ESO (visible: white), APEX (submillimeter: orange), Chandra (X-rays: blue), and Spitzer (infrared: red) images. The magnetic fields were found to be parallel to the dust lanes on the outskirts of the galaxy but distorted near the center. Gravitational forces near the black hole accelerate ions and enhance the magnetic field. In sum, the collision not only combined the galaxies’ masses -- but amplified their magnetic fields. These results provide new insights into how magnetic fields evolved in the early universe when mergers were more common.

ASTRONOMY - Ingenuity: First Flight over Mars

 2021 April 20

Ingenuity: First Flight over Mars
Video Credit: NASA, JPL-Caltech, ASU, MSSS

Explanation: What's the best way to explore Mars? Perhaps there is no single best way, but a newly demonstrated method shows tremendous promise: flight. Powered flight has the promise to search vast regions and scout out particularly interesting areas for more detailed investigation. Yesterday, for the first time, powered flight was demonstrated on Mars by a small helicopter named Ingenuity. In the featured video, Ingenuity is first imaged by the Perseverance rover sitting quietly on the Martian surface. After a few seconds, Ingenuity's long rotors begin to spin, and a few seconds after that -- history is made as Ingenuity actually takes off, hovers for a few seconds, and then lands safely. More tests of Ingenuity's unprecedented ability are planned over the next few months. Flight may help humanity better explore not only Mars, but Saturn's moon Titan over the next few decades.

MINERAUX - Le sélénite, une pierre de lune

 

Considéré comme une variété de gypse, le sélénite permet de voir « l'éclat de la Lune ». Son nom provient d'ailleurs de selentis, qui signifie « pierre de Lune » en grec. La région de Bologne, en Italie, est connue pour en contenir beaucoup. Elle fut d'ailleurs utilisée pour construire les premières fortifications de la ville, aujourd'hui disparues.

Couleur : incolore à rougeâtre.

© mockbird, Flickr, CC by-sa 2.0

ASTRONOMY - The Galactic Center in Infrared

 2021 April 19

The Galactic Center in Infrared
Image Credit: NASA, JPL-Caltech, Spitzer Space Telescope, Susan Stolovy (SSC/Caltech) et al.; Reprocessing: Judy Schmidt

Explanation: What does the center of our galaxy look like? In visible light, the Milky Way's center is hidden by clouds of obscuring dust and gas. But in this stunning vista, the Spitzer Space Telescope's infrared cameras, penetrate much of the dust revealing the stars of the crowded galactic center region. A mosaic of many smaller snapshots, the detailed, false-color image shows older, cool stars in bluish hues. Red and brown glowing dust clouds are associated with young, hot stars in stellar nurseries. The very center of the Milky Way has recently been found capable of forming newborn stars. The galactic center lies some 26,700 light-years away, toward the constellation Sagittarius. At that distance, this picture spans about 900 light-years.

OCEANS -Inimaginable profondeur

"La profondeur des océans"

ASTRONOMY - Rainbow Airglow over the Azores

 2021 April 18

Rainbow Airglow over the Azores
Image Credit & Copyright: Miguel Claro (TWAN); Rollover Annotation: Judy Schmidt

Explanation: Why would the sky glow like a giant repeating rainbow? Airglow. Now air glows all of the time, but it is usually hard to see. A disturbance however -- like an approaching storm -- may cause noticeable rippling in the Earth's atmosphere. These gravity waves are oscillations in air analogous to those created when a rock is thrown in calm water. The long-duration exposure nearly along the vertical walls of airglow likely made the undulating structure particularly visible. OK, but where do the colors originate? The deep red glow likely originates from OH molecules about 87-kilometers high, excited by ultraviolet light from the Sun. The orange and green airglow is likely caused by sodium and oxygen atoms slightly higher up. The featured image was captured during a climb up Mount Pico in the Azores of Portugal. Ground lights originate from the island of Faial in the Atlantic Ocean. A spectacular sky is visible through this banded airglow, with the central band of our Milky Way Galaxy running up the image center, and M31, the Andromeda Galaxy, visible near the top left.

ASTRONOMY - Inside the Flame Nebula

2021 April 17

Inside the Flame Nebula
Image Credit: NASA, JPL-Caltech, IPAC Infrared Science Archive - Processing: Amal Biju

Explanation: The Flame Nebula is a stand out in optical images of the dusty, crowded star forming regions toward Orion's belt and the easternmost belt star Alnitak, a mere 1,400 light-years away. Alnitak is the bright star at the right edge of this infrared image from the Spitzer Space Telescope. About 15 light-years across, the infrared view takes you inside the nebula's glowing gas and obscuring dust clouds though. It reveals many stars of the recently formed, embedded cluster NGC 2024 concentrated near the center. The stars of NGC 2024 range in age from 200,000 years to 1.5 million years young. In fact, data indicate that the youngest stars are concentrated near the middle of the Flame Nebula cluster. That's the opposite of the simplest models of star formation for a stellar nursery that predict star formation begins in the denser center of a molecular cloud core. The result requires a more complex model for star formation inside the Flame Nebula. ...........................

MINERAUX - Le béryl, un cristal d’eau de mer

Le béryl (Be₃Al₂Si₆O₁₈) est un minéral du groupe des silicates. Son nom vient du grec beryllos, qui signifie « cristal de la couleur de l'eau de mer ». Il en existe plusieurs variétés utilisées en joaillerie, comme l'aigue-marine et l'émeraude. Couleurs : variées. © Rob Lavinsky, Wikimedia Commons, CC by-sa 3.0

 

ASTRONOMY - The Galaxy, the Jet, and a Famous Black Hole

 2021 April 15

The Galaxy, the Jet, and a Famous Black Hole
Image Credit: NASA, JPL-Caltech, Event Horizon Telescope Collaboration

Explanation: Bright elliptical galaxy Messier 87 (M87) is home to the supermassive black hole captured by planet Earth's Event Horizon Telescope in the first ever image of a black hole. Giant of the Virgo galaxy cluster about 55 million light-years away, M87 is the large galaxy rendered in blue hues in this infrared image from the Spitzer Space telescope. Though M87 appears mostly featureless and cloud-like, the Spitzer image does record details of relativistic jets blasting from the galaxy's central region. Shown in the inset at top right, the jets themselves span thousands of light-years. The brighter jet seen on the right is approaching and close to our line of sight. Opposite, the shock created by the otherwise unseen receding jet lights up a fainter arc of material. Inset at bottom right, the historic black hole image is shown in context, at the center of giant galaxy and relativistic jets. Completely unresolved in the Spitzer image, the supermassive black hole surrounded by infalling material is the source of enormous energy driving the relativistic jets from the center of active galaxy M87.