ASTRONOMY - A Blue Hour Full Moon

 2021 August 26

A Blue Hour Full Moon
Image Credit & Copyright: Giorgia Hofer

Explanation: Nature photographers and other fans of planet Earth always look forward to the blue hour. That's the transition in twilight, just before sunrise or after sunset, when the Sun is below the horizon but land and sky are still suffused with a beautiful blue light. After sunset on August 21, this blue hour snapshot captured the nearly full Moon as it rose opposite the Sun, above the rugged Italian Alps from Cortina d'Ampezzo, Italy. Sharing bluish hues with the sky, the rocky pyramid of Monte Antelao, also known as the King of the Dolomites, is the region's prominent alpine peak. The moonlight is yellow, but even so this full Moon was known to some as a seasonal Blue Moon. That's because by one definition the third full Moon of a season with four full moons in it is called a Blue Moon. Recognizing a season as the time between a solstice and an equinox, this season's fourth full Moon will be rising in the blue hour of September 20, just before September's equinox.

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 disparue.

Couleur : incolore à rougeâtre.

© mockbird, Flickr, CC by-sa 2.0

ASTRONOMY - Mars Rock Rochette

 2021 August 28

Mars Rock Rochette
Image Credit: NASA, JPL-Caltech

Explanation: Taken on mission sol 180 (August 22) this sharp image from a Hazard Camera on the Perseverance rover looks out across a rock strewn floor of Jezero crater on Mars. At 52.5 centimeters (21 inches) in diameter, one of the rover's steerable front wheels is at lower left in the frame. Near center is a large rock nicknamed Rochette. Mission planners don't want to avoid Rochette though. Instead Perseverance will be instructed to reach out with its 2 meter long robotic arm and abrade the rock's surface, to determine whether it has a consistency suitable for obtaining a sample, slightly thicker than a pencil, using the rover's coring bit. Samples collected by Perseverance would be returned to Earth by a future Mars mission.

ASTRONOMY - Solar System Ball Drop

 2021 August 25

Solar System Ball Drop
Video Credit & Copyright: James O'Donoghue (JAXA) & Rami Mandow (Space Australia); Text: James O'Donoghue

Explanation: Does a ball drop faster on Earth, Jupiter, or Uranus? The featured animation shows a ball dropping from one kilometer high toward the surfaces of famous solar system bodies, assuming no air resistance. The force of gravity depends on the mass of the attracting object, with higher masses pulling down with greater forces. But gravitational force also depends on distance from the center of gravity, with shorter distances causing the ball to drop faster. Combining both mass and distance, it might be surprising to see that Uranus pulls the ball down slightly slower than Earth, despite containing over 14 times more mass. This happens because Uranus has a much lower density, which puts its cloud tops further away from its center of mass. Although the falling ball always speeds up, if you were on the ball you would not feel this acceleration because you would be in free-fall. Of the three planets mentioned, the video demonstrates a ball drops even faster on Jupiter than either Earth and Uranus.

PRATIQUE - Comment Déboucher Un Évier En 3 Étapes Faciles

L'évier de la cuisine est complètement bouché ? Il reflue et en plus, ça pue dans la maison ? Et pour ne rien arranger, ça tombe un dimanche.... Heureusement, mon plombier m'a partagé une astuce super efficace pour déboucher un évier facilement. C'est une méthode rapide et économique en 3 étapes faciles. Elle évite d'appeler un plombier ou d'utiliser des produits toxiques comme le Destop. L'astuce naturelle est de mettre du bicarbonate, du vinaigre blanc et enfin de l'eau bouillante. Regardez :

Comment faire 1. Mettez le bicarbonate dans le siphon bouché. 2. Faites chauffer le vinaigre blanc dans la casserole. 3. Versez la moitié du vinaigre blanc sur le bicarbonate. 4. Laissez mousser et agir pendant une minute. 5. Une fois la mousse estompée, versez le reste du vinaigre blanc. 6. Laissez agir au moins 30 min. 7. Faites bouillir l'eau dans la casserole. 8. Versez l'eau bouillante dans le siphon. Résultat Et voilà ! Vous avez débouché votre évier en 3 étapes faciles et rapides :-) Simple, économique et efficace, n'est-ce pas ? Même pas besoin d'appeler un plombier qui coûte un bras ou de produits ultra chimiques pour nettoyer les canalisations. C'est bon pour le porte-monnaie et la planète !

PRATIQUE/POURQUOI - Pourquoi a-t-on une meilleure réception lorsqu'on touche l'antenne d'une radio ?

En fait, le corps humain, essentiellement composé d'eau est très conducteur.

En touchant une antenne radio, le corps humain fait office d'extension de cette même antenne.

Ainsi, nous améliorons la réception de l'antenne.

Le corps humain étant en plus assez grand et avec 4 membres dirigés dans des directions souvent différentes, la probabilité de se situer dans un ''espace captant mieux" est plus importante.

ASTRONOMY - Island Universe, Cosmic Sand

 2021 August 14

Island Universe, Cosmic Sand
Image Credit & Copyright: Marzena Rogozinska

Explanation: Stars in our own Milky Way Galaxy are scattered through this eye-catching field of view. From the early hours after midnight on August 13, the 30 second exposure of the night sky over Busko-Zdroj, Poland records the colorful and bright trail of a Perseid meteor. Seen near the peak of the annual Perseid meteor shower it flashes from lower left to upper right. The hurtling grain of cosmic sand, a piece of dust from periodic comet Swift-Tuttle, vaporized as it passed through planet Earth's atmosphere at almost 60 kilometers per second. Just above and right of center, well beyond the stars of the Milky Way, lies the island universe known as M31 or the Andromeda Galaxy. The Andromeda Galaxy is the most distant object easily visible to the naked-eye, about 2.5 million light-years away. The visible meteor trail begins only about 100 kilometers above Earth's surface, though. It points back to the meteor shower radiant in the constellation Perseus off the lower left edge of the frame. Follow this bright perseid meteor trail below and left to the stars of NGC 869and NGC 884, the double star cluster in Perseus.

ASTRONOMY - Explosions from White Dwarf Star RS Oph

 2021 August 22

Explosions from White Dwarf Star RS Oph
Illustration Credit & Copyright: David A. Hardy & PPARC

Explanation: Spectacular explosions keep occurring in the binary star system named RS Ophiuchi. Every 20 years or so, the red giant star dumps enough hydrogen gas onto its companion white dwarf star to set off a brilliant thermonuclear explosion on the white dwarf's surface. At about 5,000 light years distant, the resulting nova explosions cause the RS Oph system to brighten up by a huge factor and become visible to the unaided eye. The red giant star is depicted on the right of the above drawing, while the white dwarf is at the center of the bright accretion disk on the left. As the stars orbit each other, a stream of gas moves from the giant star to the white dwarf. Astronomers speculate that at some time in the next 100,000 years, enough matter will have accumulated on the white dwarf to push it over the Chandrasekhar Limit, causing a much more powerful and final explosion known as a supernova. Starting early this month, RS Oph was again seen exploding in a bright nova.

 021 August 20

Three Perseid Nights
Image Credit & Copyright: Balint Lengyel

Explanation: Frames from a camera that spent three moonless nights under the stars create this composite night skyscape. They were recorded during August 11-13 while planet Earth was sweeping through the dusty trail of comet Swift-Tuttle. One long exposure, untracked for the foreground, and the many star tracking captures of Perseid shower meteors were taken from the village of Magyaregres, Hungary. Each aligned against the background stars, the meteor trails all point back to the annual shower's radiant in the constellation Perseus heroically standing above this rural horizon. Of course the comet dust particles are traveling along trajectories parallel to each other. The radiant effect is due only to perspective, as the parallel tracks appear to converge in the distance against the starry sky.

ASTRONOMY - Mammatus Clouds over Saskatchewan

 2021 August 11

Mammatus Clouds over Saskatchewan
Image Credit & Copyright: Michael F Johnston

Explanation: When do cloud bottoms appear like bubbles? Normally, cloud bottoms are flat. This is because moist warm air that rises and cools will condense into water droplets at a specific temperature, which usually corresponds to a very specific height. As water droplets grow, an opaque cloud forms. Under some conditions, however, cloud pockets can develop that contain large droplets of water or ice that fall into clear air as they evaporate. Such pockets may occur in turbulent air near a thunderstorm. Resulting mammatus clouds can appear especially dramatic if sunlit from the side. The mammatus clouds pictured here, lasting only a few minutes, were photographed over Regina, Saskatchewan, Canada, just after a storm in 2012.