ART FRACTAL - Benoit Mandelbrot

L’objet de fractale le plus connu porte le nom de Benoît Mandelbrot, inventeur du terme, en 1974.

Fractale de Mandelbrot

Ce brave monsieur avait poussé un cri de désespoir face à ses consorts qui étudiaient alors le monde grâce à la théorie des grands nombres, laissant de côté un bon nombre de phénomènes (comme la forme des nuages, des fleuves…). N’empêche qu’après sa gueulante, on s’est un peu plus intéressé aux objets bizarres s’empoussiérant jusqu’alors dans les tiroirs des mathématiciens.

Lartboratoire

ASTRONOMY - NGC 1672: Barred Spiral Galaxy from Hubble

2022 April 6

NGC 1672: Barred Spiral Galaxy from Hubble
Image Credit: Hubble Legacy Archive, NASA, ESA; Processing & Copyright: Daniel Nobre

Explanation: Many spiral galaxies have bars across their centers. Even our own Milky Way Galaxy is thought to have a modest central bar. Prominently barred spiral galaxy NGC 1672, featured here, was captured in spectacular detail in an image taken by the orbiting Hubble Space Telescope. Visible are dark filamentary dust lanes, young clusters of bright blue stars, red emission nebulas of glowing hydrogen gas, a long bright bar of stars across the center, and a bright active nucleus that likely houses a supermassive black hole. Light takes about 60 million years to reach us from NGC 1672, which spans about 75,000 light years across. NGC 1672, which appears toward the constellation of the Dolphinfish (Dorado), has been studied to find out how a spiral bar contributes to star formation in a galaxy's central regions.

ASTRONOMY - Seven Sisters versus California

2022 April 5

Seven Sisters versus California
Image Credit & Copyright: Neven Krcmarek

Explanation: On the upper right, dressed in blue, is the Pleiades. Also known as the Seven Sisters and M45, the Pleiades is one of the brightest and most easily visible open clusters on the sky. The Pleiades contains over 3,000 stars, is about 400 light years away, and only 13 light years across. Surrounding the stars is a spectacular blue reflection nebula made of fine dust. A common legend is that one of the brighter stars faded since the cluster was named. On the lower left, shining in red, is the California Nebula. Named for its shape, the California Nebula is much dimmer and hence harder to see than the Pleiades. Also known as NGC 1499, this mass of red glowing hydrogen gas is about 1,500 light years away. Although about 25 full moons could fit between them, the featured wide angle, deep field image composite has captured them both. A careful inspection of the deep image will also reveal the star forming region IC 348 and the molecular cloud LBN 777 (the Baby Eagle Nebula).

ASTRONOMY - A Vortex Aurora over Iceland

2022 April 4

A Vortex Aurora over Iceland
Image Credit & Copyright: Christophe Suarez

Explanation: No, the car was not in danger of being vacuumed into space by the big sky vortex. For one reason, the vortex was really an aurora, and since auroras are created by particles striking the Earth from space, they do not create a vacuum. This rapidly developing auroral display was caused by a Coronal Mass Ejection from the Sun that passed by the Earth closely enough to cause a ripple in Earth's magnetosphere. The upper red parts of the aurora occur over 250 kilometers high with its red glow created by atmospheric atomic oxygen directly energized by incoming particles. The lower green parts of the aurora occur over 100 kilometers high with its green glow created by atmospheric atomic oxygen energized indirectly by collisions with first-energized molecular nitrogen. Below 100 kilometers, there is little atomic oxygen, which is why auroras end abruptly. The concentric cylinders depict a dramatic auroral corona as seen from the side. The featured image was created from a single 3-second exposure taken in mid-March over Lake Myvatn in Iceland.

ASTRONOMY - CMB Dipole: Speeding Through the Universe

2022 April 3

CMB Dipole: Speeding Through the Universe
Image Credit: DMR, COBE, NASA, Four-Year Sky Map

Explanation: Our Earth is not at rest. The Earth moves around the Sun. The Sun orbits the center of the Milky Way Galaxy. The Milky Way Galaxy orbits in the Local Group of Galaxies. The Local Group falls toward the Virgo Cluster of Galaxies. But these speeds are less than the speed that all of these objects together move relative to the cosmic microwave background radiation (CMBR). In the featured all-sky map from the COBE satellite in 1993, microwave light in the Earth's direction of motion appears blueshifted and hence hotter, while microwave light on the opposite side of the sky is redshifted and colder. The map indicates that the Local Group moves at about 600 kilometers per second relative to this primordial radiation. This high speed was initially unexpected and its magnitude is still unexplained. Why are we moving so fast? What is out there?

ASTRONOMY - Nova Scotia Northern Lights

 2022 April 2

Nova Scotia Northern Lights
Image Credit & Copyright: Jason Dain

Explanation: This almost otherworldly display of northern lights was captured in clear skies during the early hours of March 31 from 44 degrees north latitude, planet Earth. In a five second exposure the scene looks north from Martinique Beach Provincial Park in Nova Scotia, Canada. Stars of the W-shaped constellation Cassiopeia shine well above the horizon, through the red tint of the higher altitude auroral glow. Auroral activity was anticipated by skywatchers alerted to the possibility of stormy space weather by Sun-staring spacecraft. The predicted geomagnetic storm was sparked as a coronal mass ejection, launched from prolific solar active region 2975, impacted our fair planet's magnetosphere.

PHOTOGRAPHIE - Vénus et la voie lactée

 

Le retour de la voie lactée en 2022. Photos prises à la plage de la Verne à La Seyne sur Mer, devant les pointus.

Technique : Matériel : NIKON Z6 II + Nikkor 24-70 f/4. Empilement de 50 poses : 24 mm - 15 s - f/4 - ISO 800. Traitement : Sequator + Lightroom | Date : 03.02.2022

Auteur : F. Xavier Cuvelier
https://www.photorama.fr

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.

Stelvision

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.