Moon behind Lava Fountain - Astronomy picture of the day - 2018 September 4

Moon behind Lava Fountain 
Image Credit & Copyright: Marcella Giulia Pace (GreenFlash.Photo)

Explanation: What's happened to the Moon? Nothing, but something has happened to the image of the Moon. The heat from a volcanic lava fountain in the foreground has warmed and made turbulent the air nearby, causing passing light to refract differently than usual. The result is a lava plume that appears to be melting the Moon. The featured picture was taken as the full Sturgeon Moon was setting behind Mt. Etna as it erupted in Italy about one week ago. The picture is actually a composite of two images, one taken right after the other, with the same camera and lens. The first image was a quick exposure to capture details of the setting Moon, while the second exposure, taken after the Moon set a few minutes later, was longer so as to capture details of the faint lava jets. From our Earth, we can only see the Sun, Moon, planets, and stars as they appear through the distortion of the Earth's atmosphere. This distortion can not only change the images of familiar orbs into unusual shapes, it can --unexpectedly at times -- delay sunset and moonset by several minutes.

Ciel verdâtre sous orage - Annonce de phénomènes violents ? - Météorologie

Si le ciel prend une couleur verdâtre à l’approche d’un orage, est-ce là une indication que des phénomènes violents vont se produire, comme des tornades ou des gros grêlons par exemple ? Beaucoup de personnes associent la couleur verdâtre d’un ciel orageux à l’arrivée imminente de phénomènes intenses. Cependant, est-ce une réalité physiquement démontrée ou cela tient-il plus de la légende urbaine ?

Parfois, lors de l’arrivée d’un orage, le ciel prend une couleur verdâtre. Il existe un discours populaire selon lequel cette coloration céleste serait l’indice que des phénomènes particulièrement violents sont sur le point de se produire. Sont notamment évoquées les tornades et la grosse grêle. Par exemple, dans les régions très sujettes aux tornades – comme le centre des États-Unis – l’apparition d’un ciel verdâtre devrait encourager les habitants à se mettre en sécurité dans leur cave ou dans un abri adapté. Ces associations se sont progressivement propagées comme des sortes de légendes urbaines, sans que l’on puisse facilement en démêler le vrai du faux.

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Science Post

Une comète se rapproche de la Terre - Science - Espace

Découverte en 1900 par l’astronome français Michel Giacobini, puis redécouverte en 1913 par l’astronome allemand Ernst Zinner, la comète 21P/Giacobini-Zinner s’est formée au-delà de “la ligne de gel” (ou de glace). Cette dernière est située après les orbites de Mars et de Jupiter, et effectue un tour du Soleil en 6,6 ans environ. Cette année, son orbite l’amènera non loin de notre planète. Le 10 septembre prochain, elle se positionnera à environ 58 millions de km. Sa magnitude étant estimée à 7, vous ne pourrez observer l’objet à l’œil nu, mais une simple paire de jumelles devrait suffire.

Comment la trouver ? La comète, qui se déplace actuellement dans l’espace à une vitesse de plus de 50 000 kilomètres à l’heure, traversera au cours des prochaines nuits les constellations du Cocher, des Gémeaux et de la Licorne. Pour mettre toutes les chances de votre côté, sortez vos jumelles ou votre télescope le 10 septembre prochain, entre minuit et le petit matin. Éloignez-vous également – il en va de soi – de toute pollution lumineuse, en espérant également un ciel clément. La comète d’un peu plus d’un kilomètre de diamètre devrait alors apparaître, teintée d’un bleu vert scintillant.

Science-Post

Aurora around Saturn's North Pole - Astronomy picture of the day - 2018 September 3

Aurora around Saturn's North Pole 
Image Credit: NASA, ESA, Hubble, OPAL Program, J. DePasquale (STScI), L. Lamy (Obs. Paris)

Explanation: Are Saturn's auroras like Earth's? To help answer this question, the Hubble Space Telescope and the Cassini spacecraft monitored Saturn's North Pole simultaneously during Cassini's final orbits around the gas giant in September 2017. During this time, Saturn's tilt caused its North Pole to be clearly visible from Earth. The featured image is a composite of ultraviolet images of aurora and optical images of Saturn's clouds and rings, all taken recently by Hubble. Like on Earth, Saturn's northern auroras can make total or partial rings around the pole. Unlike on Earth, however, Saturn's auroras are frequently spirals -- and more likely to peak in brightness just before midnight and dawn. In contrast to Jupiter's auroras, Saturn's auroras appear better related to connecting Saturn's internal magnetic field to the nearby, variable, solar wind. Saturn's southern auroras were similarly imaged back in 2004 when theplanet's South Pole was clearly visible to Earth.

A Powerful Solar Flare - Astronomy picture of the day - 2018 September 2

A Powerful Solar Flare 
Video Credit: SOHO Consortium, LASCO, ESA, NASA

Explanation: It was one of the most powerful solar flares in recorded history. Occurring in 2003 and seen across the electromagnetic spectrum, the Sun briefly became over 100 times brighter in X-rays than normal. The day after thistremendous X 17 solar flare -- and subsequent Coronal Mass Ejection (CME) -- energetic particles emitted from the explosions struck the Earth, creating auroras and affecting satellites. The spacecraft that took these frames -- SOHO-- was put in a turtle-like safe mode to avoid further damage from this and subsequent solar particle storms. The featured time-lapse movie condenses into 10 seconds events that occurred over 4 hours. The CME, visible around the central sun-shade, appears about three-quarters of the way through the video, while frames toward the very end are progressively noisier as protons from the explosions strike SOHO's LASCO detector. One this day in 1859, the effects of an even more powerful solar storm caused telegraphs on Earth to spark in what is known as the Carrington Event. Powerful solar storms such as these may create beautiful aurora-filled skies, but they also pose a real danger as they can damage satellites and even power grids across the Earth.

Aerosol Earth - Astronomy picture of the day - 2018 September 1

Aerosol Earth 
Model Visualization Credit: NASA Earth Observatory, GEOS FP, Joshua Stevens

Explanation: On August 23, 2018 the identification and distribution of aerosols in the Earth's atmosphere is shown in this dramatic, planet-wide visualization. Produced in real time, the Goddard Earth Observing System Forward Processing (GEOS FP) model relies on a combination of Earth-observing satellite and ground-based data to calculate the presence of types of aerosols, tiny solid particles and liquid droplets, as they circulate above the entire planet. This August 23rd model shows black carbon particles in red from combustion processes, like smoke from the fires in the United States and Canada, spreading across large stretches of North America and Africa. Sea salt aerosols are in blue, swirling above threatening typhoons near South Korea and Japan, and the hurricane looming near Hawaii. Dust shown in purple hues is blowing over African and Asian deserts. The location of cities and towns can be found from the concentrations of lights based on satellite image data of the Earth at night.

Close Mars - Astronomy picture of the day - 2018 August 31

Close Mars 
Image Credit & Copyright: D. Peach, V. Suc, Chilescope team

Explanation: Still bright in evening skies, Mars was just past opposition and closest to Earth on July 31, a mere 57.6 million kilometers away. Captured only a week later, this remarkable image shows the Red Planet's disk near its maximum size in earthbound telescopes, but still less than 1/74th the apparent diameter of a Full Moon. Broad regional surface shadings are starting to reappear in the tantalizing view as the latest planet-wide dust storm subsides. With the bright south polar cap at the bottom, the Valles Marineris extends along the center of the disk. Just below it lies the roughly circular Solis Lacus region sometimes known as the Eye of Mars. In a line, three prominent dark spots left of center are the volcanic Tharsis Montes.

The NGC 6914 Complex - Astronomy picture of the day - 2018 August 30

The NGC 6914 Complex 
Image Credit & Copyright: Ivan Eder

Explanation: A study in contrasts, this colorful skyscape features stars, dust, and glowing gas in the vicinity of NGC 6914. The complex of reflection nebulae lies some 6,000 light-years away, toward the high-flying northern constellation Cygnus and the plane of our Milky Way Galaxy. Obscuring interstellar dust clouds appear in silhouette while reddish hydrogen emission nebulae, along with the dusty blue reflection nebulae, fill the cosmic canvas. Ultraviolet radiation from the massive, hot, young stars of the extensive Cygnus OB2 association ionize the region's atomic hydrogen gas, producing the characteristic red glow as protons and electrons recombine. Embedded Cygnus OB2 stars also provide the blue starlight strongly reflected by the dust clouds. The nearly 1 degree wide telescopic field of view spans about 100 light-years at the estimated distance of NGC 6914.

Nearby Cepheid Variable RS Pup - Astronomy picture of the day - 2018 August 29

Nearby Cepheid Variable RS Pup 
Image Credit: NASA, ESA, Hubble Heritage Team; Acknowledgement: Howard Bond (STScI & Penn State U.)

Explanation: In the center is one of the most important stars on the sky. This is partly because, by coincidence, it is surrounded by a dazzling reflection nebula. Pulsating RS Puppis, the brightest star in the image center, is some ten times more massive than our Sun and on average 15,000 times more luminous. In fact, RS Pup is a Cepheid type variable star, a class of stars whose brightness is used to estimate distances to nearby galaxies as one of the first steps in establishing the cosmic distance scale. As RS Pup pulsates over a period of about 40 days, its regular changes in brightness are also seen along the nebula delayed in time, effectively a light echo. Using measurements of the time delay and angular size of the nebula, the known speed of light allows astronomers to geometrically determine the distance to RS Pup to be 6,500 light-years, with a remarkably small error of plus or minus 90 light-years. An impressive achievement for stellar astronomy, the echo-measured distance also more accurately establishes the true brightness of RS Pup, and by extension other Cepheid stars, improving the knowledge of distances to galaxies beyond the Milky Way. The featured image was taken by the Hubble Space Telescope.

Sea and Sky Glows over the Oregon Coast - Astronomy picture of the day - 2018 August 28

Sea and Sky Glows over the Oregon Coast 
Image Credit & Copyright: Rudy Montoya

Explanation: Every step caused the sand to light up blue. That glow was bioluminescence -- a blue radiance that also lights the surf in this surreal scene captured last month at Meyer's Creek Beach in Oregon, USA. Volcanic stacksdot the foreground sea, while a thin fog layer scatters light on the horizon. The rays of light spreading from the left horizon were created by car headlights on the Oregon Coast Highway (US 101), while the orange light on the right horizon emanates from a fishing boat. Visible far in the distance is the band of our Milky Way Galaxy, appearing to rise from a dark rocky outcrop. Sixteen images were added together to bring up the background Milky Way and toreduce noise.