ASTRONOMIE - Rencontre spectaculaire entre Mars et Saturne

 

Les positions respectives des planètes Mars et Saturne entre le 3 et le 7 avril 2022 vers 6h30 (heure de Paris) dans une paire de jumelles de type 10×50, avec un champ de 6 degrés.

Du côté de Mars et de Saturne, un croisement très serré se dessine : au meilleur de l’événement, les deux planètes auront une distance apparente inférieure à 20 minutes d’arc (l’équivalent des deux-tiers du diamètre lunaire) !

La rencontre est spectaculaire et aisément visible à l’œil nu bien que les deux planètes ne soient pas au maximum de leur éclat. Privilégiez simplement de les observer dans un ciel encore suffisamment noir pour les repérer : aux latitudes de la France métropolitaine, il faut donc sortir vers 6h30-6h45. Tournez-vous vers l’horizon est sud-est et repérez l’étincelante Vénus : notre duo se trouve un peu plus à droite, il s’agit de deux points à l’éclat similaire.

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ASTRONOMY - Exploring the Antennae

 2022 March 31

Exploring the Antennae
Image Credit & Copyright: Dietmar Hager, Eric Benson

Explanation: Some 60 million light-years away in the southerly constellation Corvus, two large galaxies are colliding. Stars in the two galaxies, cataloged as NGC 4038 and NGC 4039, very rarely collide in the course of the ponderous cataclysm that lasts for hundreds of millions of years. But the galaxies' large clouds of molecular gas and dust often do, triggering furious episodes of star formation near the center of the cosmic wreckage. Spanning over 500 thousand light-years, this stunning view also reveals new star clusters and matter flung far from the scene of the accident by gravitational tidal forces. The remarkably sharp ground-based image, an accumulation of 88 hours of exposure captured during 2012-2021, follows the faint tidal tails and distant background galaxies in the field of view. The suggestive overall visual appearance of the extended arcing structures gives the galaxy pair, also known as Arp 244, its popular name - The Antennae.

ASTRONOMY - Venus and Mars: Passing in the Night

 2022 March 29

Venus and Mars: Passing in the Night
Image Credit & Copyright: Carlos Kiko Fairbairn

Explanation: When two planets pass on the night sky, they can usually be seen near each other for a week or more. In the case of this planetary conjunction, Venus and Mars passed within 4 degrees of each other earlier this month. The featured image was taken a few days prior, when Venus was slowing rising in the pre-dawn sky, night by night, while Mars was slowly setting. The image, a four-part mosaic, was captured in Brazil from the small town Teresópolis. Besides Venus and Mars, the morning sky now also includes the more distant planet Saturn. Of course, these conjunctions are only angular -- Venus, Mars, and Saturn continue to orbit the Sun in very different parts of our Solar System. Next week, the angle between Saturn and Mars will drop to below a quarter of a degree.

ASTRONOMY - Gems of a Maldivean Night

 2022 March 28

Gems of a Maldivean Night
Image Credit & Copyright: Petr Horálek (ESO Photo Ambassador, Inst. of Physics in Opava)

Explanation: The southernmost part of the Milky Way contains not only the stars of the Southern Cross, but the closest star system to our Sun -- Alpha Centauri. The Southern Cross itself is topped by the bright, yellowish star Gamma Crucis. A line from Gamma Crucis through the blue star at the bottom of the cross, Acrux, points toward the south celestial pole, located just above the small island in the featured picture -- taken in early March. That island is Madivaru of the Maldives in the Indian Ocean. Against faint Milky Way starlight, the dark Coal Sack Nebula lies just left of the cross, while farther left along the Milky Way are the bright stars Alpha Centauri (left) and Beta Centauri (Hadar). Alpha Centauri A, a Sun-like star anchoring a three-star system with exoplanets, is a mere 4.3 light-years distant. Seen from Alpha Centauri, our own Sun would be a bright yellowish star in the otherwise recognizable constellation Cassiopeia.

ASTRONOMY - Titan seas refect sunlight

 2022 March 27

Titan Seas Reflect Sunlight
Image Credit: NASA, JPL-Caltech, U. Arizona, U. Idaho

Explanation: Why would the surface of Titan light up with a blinding flash? The reason: a sunglint from liquid seas. Saturn's moon Titan has numerous smooth lakes of methane that, when the angle is right, reflect sunlight as if they were mirrors. Pictured here in false-color, the robotic Cassini spacecraft that orbited Saturn from 2004 to 2017 imaged the cloud-covered Titan in 2014 in different bands of cloud-piercing infrared light. This specular reflection was so bright it saturated one of Cassini's infrared cameras. Although the sunglint was annoying -- it was also useful. The reflecting regions confirm that northern Titan houses a wide and complex array of seas with a geometry that indicates periods of significant evaporation. During its numerous passes of our Solar System's most mysterious moon, Cassini has revealed Titan to be a world with active weather -- including times when it rains a liquefied version of natural gas.

PHOTOMICROGRAPH - Teresa Zgoda - Fluorescent turtle embryo

Fluorescent turtle embryo

ASTRONOMY - Pluto at night

 2022 March 26

Pluto at Night
Image Credit: NASA, Johns Hopkins Univ./APL, Southwest Research Institute

Explanation: The night side of Pluto spans this shadowy scene. In the stunning spacebased perspective the Sun is 4.9 billion kilometers (almost 4.5 light-hours) behind the dim and distant world. It was captured by far flung New Horizons in July of 2015 when the spacecraft was at a range of some 21,000 kilometers from Pluto, about 19 minutes after its closest approach. A denizen of the Kuiper Belt in dramatic silhouette, the image also reveals Pluto's tenuous, surprisingly complex layers of hazy atmosphere. Near the top of the frame the crescent twilight landscape includes southern areas of nitrogen ice plains now formally known as Sputnik Planitia and rugged mountains of water-ice in the Norgay Montes.

ASTRONOMY - Interstellar Comet 2I Borisov

 2022 March 25

Interstellar Comet 2I Borisov
Image Credit: NASA, ESA, and D. Jewitt (UCLA) et al.

Explanation: From somewhere else in the Milky Way galaxy, Comet 2I/Borisov was just visiting the Solar System. Discovered by amateur astronomer Gennady Borisov on August 30, 2019, the first known interstellar comet is seen in these two Hubble Space Telescope images from November and December 2019. On the left, a distant background galaxy near the line-of-sight to Borisov is blurred as Hubble tracked the speeding comet and dust tail about 327 million kilometers from Earth. At right, 2I/Borisov appears shortly after perihelion, its closest approach to Sun. European Southern Observatory observations indicate that this comet may never have passed close to any star before its 2019 perihelion passage. Borisov's closest approach to our fair planet, a distance of about 290 million kilometers, came on December 28, 2019. Even though Hubble's sharp images don't resolve the comet's nucleus, they did lead to estimates of less than 1 kilometer for its diameter.

ASTRONOMY - The Bubble Nebula from Hubble

 2022 March 23

The Bubble Nebula from Hubble
Image Credit: NASA, ESA, Hubble; Processing & Copyright: Mehmet Hakan Özsaraç

Explanation: Massive stars can blow bubbles. The featured image shows perhaps the most famous of all star-bubbles, NGC 7635, also known simply as The Bubble Nebula. Although it looks delicate, the 7-light-year diameter bubble offers evidence of violent processes at work. Above and left of the Bubble's center is a hot, O-type star, several hundred thousand times more luminous and some 45-times more massive than the Sun. A fierce stellar wind and intense radiation from that star has blasted out the structure of glowing gas against denser material in a surrounding molecular cloud. The intriguing Bubble Nebula and associated cloud complex lie a mere 7,100 light-years away toward the boastful constellation Cassiopeia. This sharp, tantalizing view of the cosmic bubble is a reprocessed composite of previously acquired Hubble Space Telescope image data.

ASTRONOMY - A Whale of an Aurora over Swedish Forest

 2022 March 22

A Whale of an Aurora over Swedish Forest
Image Credit & Copyright: Göran Strand

Explanation: What's that in the sky? An aurora. A large coronal mass ejection occurred on our Sun earlier this month, throwing a cloud of fast-moving electrons, protons, and ions toward the Earth. Part of this cloud impacted our Earth's magnetosphere and, bolstered by a sudden gap, resulted in spectacular auroras being seen at some high northern latitudes. Featured here is a particularly photogenic auroral corona captured above a forest in Sweden from a scenic perch overlooking the city of Östersund. To some, this shimmering green glow of recombining atmospheric oxygen might appear like a large whale, but feel free to share what it looks like to you. The unusually quiet Sun of the past few years has now passed. As our Sun now approaches a solar maximum in its 11-year solar magnetic cycle, dramatic auroras like this are sure to continue.