ASTRONOMY - Crescents of Venus

 2023 August 26

Crescents of Venus
Image Credit & Copyright: Roberto Ortu

Explanation: Just as the Moon goes through phases, Venus' visible sunlit hemisphere waxes and wanes. This sequence of telescopic images illustrates the steady changes for Venus during its recent 2023 apparition as our evening star. Gliding along its interior orbit between Earth and Sun, Venus grows larger during that period because it is approaching planet Earth. Its crescent narrows though, as the inner planet swings closer to our line-of-sight to the Sun. Closest to the Earth-Sun line but passing about 8 degrees south of the Sun, on August 13 Venus reached its (non-judgmental) inferior conjunction. And now Venus shines above the eastern horizon in predawn skies, completing its transition to planet Earth's morning star. On August 21, NASA's Parker Solar Probe completed its sixth gravity assist flyby of Venus, using the encounter to maneuver the probe toward its closest approach yet to the Sun.

MUSIC - Anna Comellas (violoncelle) et Rosalind Beall (guitare) - Scarborough fair

"Scarborough fair"

METEO EXTREME - Fort risque de "Medicane" en Mediterranée

La canicule marine qui touche la mer Méditerranée cet été pourrait constituer un terrain favorable à la création d'un phénomène climatique extrême cet automne : un «medicane». Conséquence directe du réchauffement global, celui-ci inquiète les spécialistes météo.

On l'appelle medicane et si le terme est quasiment inconnu pour le grand public, les prochaines années pourraient le voir devenir tristement populaire. Ce néologisme est né de la contraction de deux mots : Méditerranée et Hurricane (ouragan en anglais).

Et si le bassin méditerranéen était, jusqu'à ces dernières années, relativement épargné par ce type de phénomène météo extrême, le réchauffement climatique pourrait multiplier la probabilité d'un tel danger. A tel point que les scientifiques ne seraient pas surpris d'alerter la population cet automne.

UNE PROBABILITÉ ACCRUE CETTE ANNÉE

Car toutes les conditions semblent réunies pour assister à la formation d'un medicane. Bien sûr, il est en ce mois d'août encore impossible de prévoir la météo à plus de 15 jours, mais ce qui inquiète les météorologues est la période de canicule marine traversée cet été par la Méditerranée, avec des eaux atteignant des températures de 30° C, soit 5 à 6 degrés de plus que la normale.Pour les spécialistes, c'est le refroidissement brutal des eaux à la fin d'un été particulièrement intense et chaud qui pourrait être la clé pour la formation d'un medicane. Car pour créer un tel ouragan, l'air humide et chaud près de la mer va devoir rencontrer une masse d'air froid, que l'automne pourrait amener, rapporte Météo France. Deux facteurs d'instabilité qui peuvent occasionner de violents orages.

CNews

ASTRONOMY - A Season of Saturn

 2023 August 25

A Season of Saturn
Image Credit & Copyright: Andy Casely

Explanation: Ringed planet Saturn will be at its 2023 opposition, opposite the Sun in Earth's skies, on August 27. While that puts the sixth planet from the Sun at its brightest and well-placed for viewing, its beautiful ring system isn't visible to the unaided eye. Still, this sequence of telescopic images taken a year apart over the last six years follows both Saturn and rings as seen from inner planet Earth. The gas giant's ring plane tilts from most open in 2018 to approaching edge-on in 2023 (top to bottom). That's summer to nearly the autumn equinox for Saturn's northern hemisphere. In the sharp planetary portraits, Saturn's northern hexagon and a large storm system are clearly visible in 2018. In 2023, ice moon Tethys is transiting, casting its shadow across southern hemisphere cloud bands, while Saturn's cold blue south pole is emerging from almost a decade of winter darkness.

METEO EXTREME - Nuage impressionnant dans le Nord de la France

Orages dans le nord : fortes rafales, grêle et un impressionnant nuage arcus en Normandie

Grêle, puissantes rafales et surtout, un nuage très particulier : ce jeudi 24 août, l’épisode orageux qui balaie le nord-est de la France a été annoncé en Normandie par un arcus spectaculaire, comme vous pouvez le voir dans notre vidéo en tête de l’article. Sur les réseaux sociaux, des images capturées à Trouville-sur-Mer ou encore au Havre, montrent ce nuage à l’apparence menaçante avancer dans le ciel. Ce phénomène météorologique impressionnant est défini par Météo-France comme un « long rouleau horizontal situé à l’avant d’un nuage d’orage ». Il se forme lorsque l’air chaud qui alimente un nuage d’orage par l’avant surmonte l’air froid entraîné vers le bas par des précipitations intenses. Ce jeudi matin, l’arcus aperçu en Normandie était accompagné de fortes rafales atteignant jusqu’à 100 km/h selon l’Observatoire français des tornades et orages violents, 

LeHuffPost

ASTRONOMY - Meteors along the Milky Way

 2023 August 24

Meteors along the Milky Way
Image Credit & Copyright: Ali Hosseini Nezhad

Explanation: Under dark and mostly moonless night skies, many denizens of planet Earth were able to watch this year's Perseid meteor shower. Seen from a grassy hillside from Shiraz, Iran these Perseid meteors streak along the northern summer Milky Way before dawn on Sunday, August 13. Frames used to construct the composited image were captured near the active annual meteor shower's peak between 02:00 AM and 04:30 AM local time. Not in this night skyscape, the shower's radiant in the heroic constellation Perseus is far above the camera's field of view. But fans of northern summer nights can still spot a familiar asterism. Formed by bright stars Deneb, Vega, and Altair, the Summer Triangle spans the luminous band of the Milky Way.

ASTRONOMY - The Meteor and the Galaxy

 2023 August 23

The Meteor and the Galaxy
Credit & Copyright: Jose Pedrero

Explanation: It came from outer space. It -- in this case a sand-sized bit of a comet nucleus -- was likely ejected many years ago from Sun-orbiting Comet Swift-Tuttle, but then continued to orbit the Sun alone. When the Earth crossed through this orbit, the piece of comet debris impacted the atmosphere of our fair planet and was seen as a meteor. This meteor deteriorated, causing gases to be emitted that glowed in colors emitted by its component elements. The featured image was taken last week from Castilla La Mancha, Spain, during the peak night of the Perseids meteor shower. The picturesque meteor streak happened to appear in the only one of 50 frames that also included the Andromeda galaxy. Stars dot the frame, each much further away than the meteor. Compared to the stars, the Andromeda galaxy (M31) is, again, much further away.

ASTRONOMY - M16: Eagle Nebula Deep Field

 2023 May 15

M16: Eagle Nebula Deep Field
Image Credit & Copyright: Gianni Lacroce

Explanation: From afar, the whole thing looks like an eagle. A closer look at the Eagle Nebula, however, shows the bright region is actually a window into the center of a larger dark shell of dust. Through this window, a brightly-lit workshop appears where a whole open cluster of stars is being formed. In this cavity, tall pillars and round globules of dark dust and cold molecular gas remain where stars are still forming. Already visible are several young bright blue stars whose light and winds are burning away and pushing back the remaining filaments and walls of gas and dust. The Eagle emission nebula, tagged M16, lies about 6500 light years away, spans about 20 light-years, and is visible with binoculars toward the constellation of the Serpent (Serpens). This picture involved long and deep exposures and combined three specific emitted colors emitted by sulfur (colored as yellow), hydrogen (red), and oxygen (blue).

ASTRONOMY - Moons Across Jupiter

 2023 June 13

Moons Across Jupiter
Image Credit: NASA; ESA, JPL, Cassini Imaging Team, SSI; Processing: Kevin M. Gill

Explanation: Jupiter's moons circle Jupiter. The featured video depicts Europa and Io, two of Jupiter's largest moons, crossing in front of the grand planet's Great Red Spot, the largest known storm system in our Solar System. The video was composed from images taken by the robotic Cassini spacecraft as it passed Jupiter in 2000, on its way to Saturn. The two moons visible are volcanic Io, in the distance, and icy Europa. In the time-lapse video, Europa appears to overtake Io, which is odd because Io is closer to Jupiter and moves faster. The explanation is that the motion of the fast Cassini spacecraft changes the camera location significantly during imaging. Jupiter is currently being visited by NASA's robotic Juno spacecraft, while ESA's Jupiter Icy Moons Explorer (JUICE), launched in April, is enroute.

A Roll Cloud Over Wisconsin

 2023 August 20

A Roll Cloud Over Wisconsin
Credit: Megan Hanrahan (Pierre cb), Wikipedia

Explanation: What kind of cloud is this? A type of arcus cloud called a roll cloud. These rare long clouds may form near advancing cold fronts. In particular, a downdraft from an advancing storm front can cause moist warm air to rise, cool below its dew point, and so form a cloud. When this happens uniformly along an extended front, a roll cloud may form. Roll clouds may actually have air circulating along the long horizontal axis of the cloud. A roll cloud is not thought to be able to morph into a tornado. Unlike a similar shelf cloud, a roll cloud is completely detached from their parent cumulonimbus cloud. Pictured here, a roll cloud extends far into the distance as a storm approaches in 2007 in Racine, Wisconsin, USA.