Exoplanet WASP-12b

Astronomers have discovered that the well-studied exoplanet WASP-12b reflects almost no light, making it appear essentially pitch black. This discovery sheds new light on the atmospheric composition of the planet and also refutes previous hypotheses about WASP-12b’s atmosphere. The results are also in stark contrast to observations of another similarly sized exoplanet.

Using the Space Telescope Imaging Spectrograph (STIS) on the NASA/ESA Hubble Space Telescope, an international team led by astronomers at McGill University, Canada, and the University of Exeter, UK, have measured how much light the exoplanet WASP-12b reflects — its albedo — in order to learn more about the composition of its atmosphere.

The results were surprising, explains lead author Taylor Bell, a Master’s student in astronomy at McGill University who is affiliated with the Institute for Research on Exoplanets: “The measured albedo of WASP-12b is 0.064 at most. This is an extremely low value, making the planet darker than fresh asphalt!” This makes WASP-12b two times less reflective than our Moon which has an albedo of 0.12. Bell adds: “The low albedo shows we still have a lot to learn about WASP-12b and other similar exoplanets.”

WASP-12b orbits the Sun-like star WASP-12A, about 1400 light-years away, and since its discovery in 2008 it has become one of the best studied exoplanets. With a radius almost twice that of Jupiter and a year of just over one Earth day, WASP-12b is categorised as a hot Jupiter. Because it is so close to its parent star, the gravitational pull of the star has stretched WASP-12b into an egg shape and raised the surface temperature of its daylight side to 2600 degrees Celsius.

The high temperature is also the most likely explanation for WASP-12b’s low albedo. “There are other hot Jupiters that have been found to be remarkably black, but they are much cooler than WASP-12b. For those planets, it is suggested that things like clouds and alkali metals are the reason for the absorption of light, but those don’t work for WASP-12b because it is so incredibly hot," explains Bell.

The daylight side of WASP-12b is so hot that clouds cannot form and alkali metals are ionised. It is even hot enough to break up hydrogen molecules into atomic hydrogen which causes the atmosphere to act more like the atmosphere of a low-mass star than like a planetary atmosphere. This leads to the low albedo of the exoplanet.

To measure the albedo of WASP-12b the scientists observed the exoplanet in October 2016 during an eclipse, when the planet was near full phase and passed behind its host star for a time. This is the best method to determine the albedo of an exoplanet, as it involves directly measuring the amount of light being reflected. However, this technique requires a precision ten times greater than traditional transit observations. Using Hubble’s Space Telescope Imaging Spectrograph the scientists were able to measure the albedo of WASP-12b at several different wavelengths.

“After we measured the albedo we compared it to spectral models of previously suggested atmospheric models of WASP-12b”, explains Nikolay Nikolov (University of Exeter, UK), co-author of the study. “We found that the data match neither of the two currently proposed models.” The new data indicate that the WASP-12b atmosphere is composed of atomic hydrogen and helium.

WASP-12b is only the second planet to have spectrally resolved albedo measurements, the first being HD 189733b, another hot Jupiter. The data gathered by Bell and his team allowed them to determine whether the planet reflects more light towards the blue or the red end of the spectrum. While the results for HD 189733b suggest that the exoplanet has a deep blue colour, WASP-12b, on the other hand, is not reflecting light at any wavelength. WASP-12b does, however, emit light because of its high temperature, giving it a red hue similar to a hot glowing metal.

“The fact that the first two exoplanets with measured spectral albedo exhibit significant differences demonstrates the importance of these types of spectral observations and highlights the great diversity among hot Jupiters,” concludes Bell.

Image Credit: NASA, ESA, and G. Bacon (STScI)
Explanation from: https://www.spacetelescope.org/news/heic1714/

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Spiral Galaxy NGC 6384

The NASA/ESA Hubble Space Telescope has produced this finely detailed image of the beautiful spiral galaxy NGC 6384. This galaxy lies in the constellation of Ophiuchus (The Serpent Bearer), not far from the centre of the Milky Way on the sky. The positioning of NGC 6384 means that we have to peer at it past many dazzling foreground Milky Way stars that are scattered across this image.

In 1971, one member of NGC 6384 stood out against these bright foreground stars when one of its stars exploded as a supernova. This was a Type Ia supernova, which occurs when a compact star that has ceased fusion in its core, called a white dwarf, increases its mass beyond a critical limit by gobbling up matter from a companion star. A runaway nuclear explosion then makes the star suddenly as bright as a whole galaxy.

While many stars have already come to the ends of their lives in NGC 6384, in the centre, star formation is being fuelled by the galaxy’s bar structure; astronomers think such galactic bars funnel gas inwards, where it accumulates to form new stars.

This picture was created from images take with the Wide Field Channel of Hubble’s Advanced Camera for Surveys. An image taken through a blue filter (F435W, coloured blue) was combined with an image taken through a near-infrared filter (F814W, coloured red). The total exposure times were 1050 s through each filter and the field of view is about 3 x 1.5 arcminutes.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1108a/

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Star-Forming Region NGC 6729

This image from ESO’s Very Large Telescope gives a close-up view of the dramatic effects new-born stars have on the gas and dust from which they formed. Although the stars themselves are not visible, material they have ejected is colliding with the surrounding gas and dust clouds and creating a surreal landscape of glowing arcs, blobs and streaks.

The star-forming region NGC 6729 is part of one of the closest stellar nurseries to the Earth and hence one of the best studied. This new image from ESO’s Very Large Telescope gives a close-up view of a section of this strange and fascinating region. The data were selected from the ESO archive by Sergey Stepanenko as part of the Hidden Treasures competition. Sergey’s picture of NGC 6729 was ranked third in the competition.

Stars form deep within molecular clouds and the earliest stages of their development cannot be seen in visible-light telescopes because of obscuration by dust. In this image there are very young stars at the upper left of the picture. Although they cannot be seen directly, the havoc that they have wreaked on their surroundings dominates the picture. High-speed jets of material that travel away from the baby stars at velocities as high as one million kilometres per hour are slamming into the surrounding gas and creating shock waves. These shocks cause the gas to shine and create the strangely coloured glowing arcs and blobs known as Herbig–Haro objects.

In this view the Herbig–Haro objects form two lines marking out the probable directions of ejected material. One stretches from the upper left to the lower centre, ending in the bright, circular group of glowing blobs and arcs at the lower centre. The other starts near the left upper edge of the picture and extends towards the centre right. The peculiar scimitar-shaped bright feature at the upper left is probably mostly due to starlight being reflected from dust and is not a Herbig–Haro object.

This enhanced-colour picture was created from images taken using the FORS1 instrument on ESO’s Very Large Telescope. Images were taken through two different filters that isolate the light coming from glowing hydrogen (shown as orange) and glowing ionised sulphur (shown as blue). The different colours in different parts of this violent star formation region reflect different conditions — for example where ionised sulphur is glowing brightly (blue features) the velocities of the colliding material are relatively low — and help astronomers to unravel what is going on in this dramatic scene.

Image Credit: ESO
Explanation from: https://www.eso.org/public/news/eso1109/

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Alpha Centauri and Beta Centauri

At the centre of this image of the Centaurus constellation are Alpha Centauri and Beta Centauri, two triple star systems. The brightest stars of both systems orbit near to each other, making them appear as one star. Alpha Centauri is the nearest "star" to Earth except for the Sun. This photograph of the Centaurus constellation was taken at ESO's La Silla Observatory.

Image Credit: ESO
Explanation from: https://www.eso.org/public/images/centaurus-ch17-bardon-cc/

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Exoplanet WASP-19b

Astronomers using ESO’s Very Large Telescope have detected titanium oxide in an exoplanet atmosphere for the first time. This discovery around the hot-Jupiter planet WASP-19b exploited the power of the FORS2 instrument. It provides unique information about the chemical composition and the temperature and pressure structure of the atmosphere of this unusual and very hot world.

A team of astronomers led by Elyar Sedaghati, an ESO fellow and recent graduate of TU Berlin, has examined the atmosphere of the exoplanet WASP-19b in greater detail than ever before. This remarkable planet has about the same mass as Jupiter, but is so close to its parent star that it completes an orbit in just 19 hours and its atmosphere is estimated to have a temperature of about 2000 degrees Celsius.

As WASP-19b passes in front of its parent star, some of the starlight passes through the planet’s atmosphere and leaves subtle fingerprints in the light that eventually reaches Earth. By using the FORS2 instrument on the Very Large Telescope the team was able to carefully analyse this light and deduce that the atmosphere contained small amounts of titanium oxide, water and traces of sodium, alongside a strongly scattering global haze.

“Detecting such molecules is, however, no simple feat,” explains Elyar Sedaghati, who spent 2 years as ESO student to work on this project. “Not only do we need data of exceptional quality, but we also need to perform a sophisticated analysis. We used an algorithm that explores many millions of spectra spanning a wide range of chemical compositions, temperatures, and cloud or haze properties in order to draw our conclusions.”

Titanium oxide is rarely seen on Earth. It is known to exist in the atmospheres of cool stars. In the atmospheres of hot planets like WASP-19b, it acts as a heat absorber. If present in large enough quantities, these molecules prevent heat from entering or escaping through the atmosphere, leading to a thermal inversion — the temperature is higher in the upper atmosphere and lower further down, the opposite of the normal situation. Ozone plays a similar role in Earth’s atmosphere, where it causes inversion in the stratosphere.

“The presence of titanium oxide in the atmosphere of WASP-19b can have substantial effects on the atmospheric temperature structure and circulation.” explains Ryan MacDonald, another team member and an astronomer at Cambridge University, United Kingdom. “To be able to examine exoplanets at this level of detail is promising and very exciting.” adds Nikku Madhusudhan from Cambridge University who oversaw the theoretical interpretation of the observations.

The astronomers collected observations of WASP-19b over a period of more than one year. By measuring the relative variations in the planet’s radius at different wavelengths of light that passed through the exoplanet’s atmosphere and comparing the observations to atmospheric models, they could extrapolate different properties, such as the chemical content, of the exoplanet’s atmosphere.

This new information about the presence of metal oxides like titanium oxide and other substances will allow much better modeling of exoplanet atmospheres. Looking to the future, once astronomers are able to observe atmospheres of possibly habitable planets, the improved models will give them a much better idea of how to interpret those observations.

“This important discovery is the outcome of a refurbishment of the FORS2 instrument that was done exactly for this purpose,” adds team member Henri Boffin, from ESO, who led the refurbishment project. “Since then, FORS2 has become the best instrument to perform this kind of study from the ground.”

Image Credit: ESO/M. Kornmesser
Explanation from: https://www.eso.org/public/news/eso1729/

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Jupiter seen by NASA's Juno spacecraft

This series of enhanced-color images shows Jupiter up close and personal, as NASA's Juno spacecraft performed its eighth flyby of the gas giant planet. The images were obtained by JunoCam.

From left to right, the sequence of images taken on September 1, 2017 from 3:03 p.m. to 3:11 p.m. PDT (6:03 p.m. to 6:11 p.m. EDT). At the times the images were taken, the spacecraft ranged from 7,545 to 14,234 miles (12,143 to 22,908 kilometers) from the tops of the clouds of the planet at a latitude range of -28.5406 to -44.4912 degrees.

Image Credit: NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstadt/Sean Doran
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA21780

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Earth and three hurricanes seen by Suomi NPP satellite

There was no shortage of storms brewing across the Atlantic basin in September 2017. On September 6, hurricanes Katia, Irma, and Jose lined up across the basin. The trio is visible in this image, captured that day by the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite. The image is a mosaic, assembled from images acquired throughout the day during several orbits of the satellite.

On September 6, Katia had strengthened over the southwestern Gulf of Mexico and was upgraded from tropical storm to hurricane status. The eye of Irma, a raging category 5 storm, passed north of Puerto Rico but still delivered strong winds and rain the Caribbean island. Meanwhile, Jose spun in the central Atlantic Ocean, and was also upgraded that day from a tropical storm to hurricane.

The bright strips are reflected sunlight, or “glint,” which show up over ocean areas in the middle of each orbit.

Image Credit: NASA Earth Observatory
Explanation from: https://earthobservatory.nasa.gov/NaturalHazards/view.php?id=90918

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In search of exoplanets

The Search for habitable Planets EClipsing ULtra-cOOl Stars (SPECULOOS) telescope will search for terrestrial exoplanets around nearby ultracool stars and brown dwarfs when it has first light in December 2017. SPECULOOS joins a fleet of exoplanet-searching telescopes, including the two TRAnsiting Planets and PlanetesImals Small Telescopes(TRAPPIST)— one at ESO’s La Silla Observatory in Chile and another at Oukaïmden Observatory in Morocco.

Image Credit: H. Zodet/ESO
Explanation from: https://www.eso.org/public/images/upr-kh9a0928-cc/

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X8.2 Solar Flare

The Sun emitted a significant solar flare, peaking at 12:06 p.m. EDT on September 10, 2017. NASA’s Solar Dynamics Observatory, which watches the Sun constantly, captured an image of the event. Solar flares are powerful bursts of radiation. Harmful radiation from a flare cannot pass through Earth's atmosphere to physically affect humans on the ground, however — when intense enough — they can disturb the atmosphere in the layer where GPS and communications signals travel.

This flare is classified as an X8.2-class flare. X-class denotes the most intense flares, while the number provides more information about its strength. An X2 is twice as intense as an X1, an X3 is three times as intense, etc.

This flare is the capstone on a series of flares from Active Region 2673, which was identified on August 29 and is currently rotating off the front of the Sun as part of our star’s normal rotation.

Image Credit: NASA/SDO/Goddard
Explanation from: https://www.nasa.gov/feature/goddard/2017/active-region-on-sun-continues-to-emit-solar-flares

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Smoke over the United States seen by Suomi NPP satellite

With dozens of wildfires burning across the western United States and Canada, many North Americans have had the acrid taste of smoke in their mouths during the past few weeks. On September 5, 2017, the National Interagency Fire Center (NIFC) reported more than 80 large fires burning in nine western U.S. states. People living in large stretches of northern California, Oregon, Washington, Montana, and Idaho have been breathing what the U.S. government’s Air Now website rated as “hazardous” air.

The natural-color mosaic above was made from several scenes acquired on September 4, 2017, by the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi National Polar-orbiting Partnership (Suomi-NPP) satellite. The Ozone Mapper Profiler Suite (OMPS) on Suomi NPP also collected data on airborne aerosols as they were swept by winds from west to east across the continental United States (second image).

The OMPS map depicts relative aerosol concentrations, with lower concentrations appearing in yellow and higher concentrations appearing in dark orange-brown. Note that the sensor detects aerosols in high-altitude plumes more readily than lower plumes, so this map does not reflect air quality conditions at “nose height.” Rather it shows where large plumes of smoke were lofted several kilometers up into the atmosphere.

On September 5, roughly 7.8 million acres had burned in the United States since the beginning of 2017, according to NIFC. “While it is unlikely that this season will be record-breaking for modern fire record keeping in the western United States, it is above normal relative to the last decade—which has seen abundant fire activity,” said John Abatzoglou, a fire researcher at the University of Idaho. Unusually warm and dry conditions across a broad swath of the West has fueled the active fire season, noted Abatzoglou. A wet winter in some parts of the West also contributed by triggering the growth of more grass in the spring—grass that turns into fuel for fires in the summer.

Image Credit: NASA Earth Observatory
Explanation from: https://earthobservatory.nasa.gov/IOTD/view.php?id=90899

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Saturn seen by Cassini spacecraft

With this view, Cassini captured one of its last looks at Saturn and its main rings from a distance. The Saturn system has been Cassini's home for 13 years, but that journey is nearing its end.

Cassini has been orbiting Saturn for nearly a half of a Saturnian year but that journey is nearing its end. This extended stay has permitted observations of the long-term variability of the planet, moons, rings, and magnetosphere, observations not possible from short, fly-by style missions.

When the spacecraft arrived at Saturn in 2004, the planet's northern hemisphere, seen here at top, was in darkness, just beginning to emerge from winter. Now at journey's end, the entire north pole is bathed in the continuous sunlight of summer.

Images taken on October 28, 2016 with the wide angle camera using red, green and blue spectral filters were combined to create this color view. This view looks toward the sunlit side of the rings from about 25 degrees above the ringplane.

The view was acquired at a distance of approximately 870,000 miles (1.4 million kilometers) from Saturn. Image scale is 50 miles (80 kilometers) per pixel.

Image Credit: NASA/JPL-Caltech/Space Science Institute
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA21345

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Spiral Galaxy NGC 5398

This NASA/ESA Hubble Space Telescope picture shows NGC 5398, a barred spiral galaxy located about 55 million light-years away.

The galaxy is famous for containing an especially extensive HII region, a large cloud composed of ionised hydrogen (or HII, pronounced “H-two”, with H being the chemical symbol for hydrogen and the “II” indicating that the atoms have lost an electron to become ionised). NGC 5398’s cloud is named Tol 89 and sits at the lower left end of the galaxy’s central “bar” of stars, a structure that cuts through the galactic core and funnels material inwards to maintain the star formation occurring there.

Tol 86 is conspicuous in being the only large massive star forming complex in the entire galaxy, with an extension of roughly 5000 times 4000 light-years; it contains at least seven young and massive star clusters. The two brightest clumps within Tol 89, which astronomers have named simply “A” and “B”, appear to have undergone two bursts of star-forming activity — “starbursts” — roughly 4 million and less than 3 million years ago respectively. Tol 89-A is thought to contain a number of particularly bright and massive stars known as Wolf-Rayet stars, which are known for their high temperatures and extreme stellar winds.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1737a/

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Three hurricanes seen by Suomi NPP satellite

Meteorologists struggled to find the right words to describe the situation as a line of three hurricanes—two of them major and all of them threatening land—brewed in the Atlantic basin in September 2017.

Forecasters were most concerned about Irma, which was on track to make landfall in densely populated South Florida on September 10 as a large category 4 storm. Meanwhile, category 2 Hurricane Katia was headed for Mexico, where it was expected to make landfall on September 9. And just days after Irma devastated the Leeward Islands, the chain of small Caribbean islands braced for another blow—this time from category 4 Hurricane Jose.

The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite captured the data for a mosaic of Katia, Irma, and Jose as they appeared in the early hours of September 8, 2017. The images were acquired by the VIIRS “day-night band,” which detects light signals in a range of wavelengths from green to near-infrared, and uses filtering techniques to observe signals such as city lights, auroras, wildfires, and reflected moonlight. In this case, the clouds were lit by the nearly full Moon. The image is a composite, showing cloud imagery combined with data on city lights.

As all three storms approach land, meteorologists will be using assets on the ground, in air, and in space to track them. “Our human assets and aircraft penetrations are critical but limited,” said Marshall Shepherd, an atmospheric scientist at the University of Georgia. “Satellites provide a unique perspective on clouds, rainfall, sea surface state, sea surface temperature, and more. Only the satellite vantage point can provide continuous coverage of all three storms without having to refuel or sleep.”

Image Credit: NASA Earth Observatory
Explanation from: https://earthobservatory.nasa.gov/IOTD/view.php?id=90931

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Interacting Galaxies NGC 2207 • IC 2163

• NGC 2207 and IC 2163 are two spiral galaxies in the process of merging.

• This pair contains a large collection of super bright X-ray objects called "ultraluminous X-ray sources" (ULXs).

• Astronomers have found evidence for three supernova explosions within this pair in the past 15 years.

• A new composite image of the system contains X-rays from Chandra (pink) along with optical and infrared data.

At this time of year, there are lots of gatherings often decorated with festive lights. When galaxies get together, there is the chance of a spectacular light show as is the case with NGC 2207 and IC 2163

Located about 130 million light years from Earth, in the constellation of Canis Major, this pair of spiral galaxies has been caught in a grazing encounter. NGC 2207 and IC 2163 have hosted three supernova explosions in the past 15 years and have produced one of the most bountiful collections of super bright X-ray lights known. These special objects — known as "ultraluminous X-ray sources" (ULXs) — have been found using data from NASA's Chandra X-ray Observatory.

As in our Milky Way galaxy, NGC 2207 and IC 2163 are sprinkled with many star systems known as X-ray binaries, which consist of a star in a tight orbit around either a neutron star or a "stellar-mass" black hole. The strong gravity of the neutron star or black hole pulls matter from the companion star. As this matter falls toward the neutron star or black hole, it is heated to millions of degrees and generates X-rays.

ULXs have far brighter X-rays than most "normal" X-ray binaries. The true nature of ULXs is still debated, but they are likely a peculiar type of X-ray binary. The black holes in some ULXs may be heavier than stellar mass black holes and could represent a hypothesized, but as yet unconfirmed, intermediate-mass category of black holes.

This composite image of NGC 2207 and IC 2163 contains Chandra data in pink, optical light data from the Hubble Space Telescope in red, green, and blue (appearing as blue, white, orange, and brown), and infrared data from the Spitzer Space Telescope in red.

The new Chandra image contains about five times more observing time than previous efforts to study ULXs in this galaxy pair. Scientists now tally a total of 28 ULXs between NGC 2207 and IC 2163. Twelve of these vary over a span of several years, including seven that were not detected before because they were in a "quiet" phase during earlier observations.

The scientists involved in studying this system note that there is a strong correlation between the number of X-ray sources in different regions of the galaxies and the rate at which stars are forming in these regions. The composite image shows this correlation through X-ray sources concentrated in the spiral arms of the galaxies, where large amounts of stars are known to be forming. This correlation also suggests that the companion star in the binary systems is young and massive.

Colliding galaxies like this pair are well known to contain intense star formation. Shock waves — like the sonic booms from supersonic aircraft — form during the collision, leading to the collapse of clouds of gas and the formation of star clusters. In fact, researchers estimate that the stars associated with the ULXs are very young and may only be about 10 million years old. In contrast, our Sun is about halfway through its 10-billion-year lifetime. Moreover, analysis shows that stars of various masses are forming in this galaxy pair at a rate equivalent to form 24 stars the mass of our sun per year. In comparison, a galaxy like our Milky Way is expected to spawn new stars at a rate equivalent to only about one to three new suns every year.

Image Credit: X-ray: NASA/CXC/SAO/S.Mineo et al, Optical: NASA/STScI, Infrared: NASA/JPL-Caltech
Explanation from: http://chandra.si.edu/photo/2014/ngc2207/

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Star-Forming Region Messier 43

The NASA/ESA Hubble Space Telescope has taken a close-up view of an outer part of the Orion Nebula’s little brother, Messier 43. This nebula, which is sometimes referred to as De Mairan’s Nebula after its discoverer, is separated from the famous Orion Nebula (Messier 42) by only a dark lane of dust. Both nebulae are part of the massive stellar nursery called the Orion molecular cloud complex, which includes several other nebulae, such as the Horsehead Nebula (Barnard 33) and the Flame Nebula (NGC 2024).

The Orion molecular cloud complex is about 1400 light-years away, making it one of the closest massive star formation regions to Earth. Hubble has therefore studied this extraordinary region extensively over the past two decades, monitoring how stellar winds sculpt the clouds of gas, studying young stars and their surroundings and discovering many elusive objects, such as brown dwarf stars.

This view shows several of the brilliant hot young stars in this less-studied region and it also reveals many of the curious features around even younger stars that are still cocooned by dust.

This picture was created from images taken using the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images through yellow (F555W, coloured blue) and near-infrared (F814W, coloured red) filters were combined. The exposure times were 1000 s per filter and the field of view is about 3.3 arcminutes across.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1109a/

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Hurricane Irma seen by NASA’s Terra satellite

The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite acquired a natural-color image of Irma at 10:00 a.m. local time (16:00 Universal Time) on September 8, 2017.

Image Credit: NASA

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Dwarf Galaxy IC 2574

The NASA/ESA Hubble Space Telescope has imaged a region of space containing the intriguing object IC 2574. Pink bubbles blown by supernova explosions abound in this faint galaxy. The colour of these shells comes from hydrogen gas irradiated by newborn stars. The formation of the stars was triggered by shock waves from earlier supernova detonations that compressed material together.

IC 2574 is commonly known as Coddington's Nebula after the American astronomer Edwin Coddington, who discovered it in 1898. Astronomers classify IC 2574 as a dwarf irregular galaxy due to its relatively small size and lack of organisation or structure. These galaxies are thought to resemble some of the earliest that formed in the Universe. Dwarf irregular galaxies thus serve as useful "living fossils" for studying the evolution of more complex galaxy types such as our home, the Milky Way, with its central bar and spiral arms. The expanding shells in IC 2574 are of particular interest to astronomers as they reveal how supernova-driven explosions ignite round after round of star formation.

The constellation containing IC 2574 is Ursa Major (The Great Bear). IC 2574 is located about 12 million light-years away, belonging to the Messier 81 group of galaxies. This group is named after the most prominent galaxy in its midst, the big, bright and accordingly well-studied spiral galaxy Messier 81.

This picture was produced with Hubble’s Advanced Camera for Surveys, and covers a field of view of around 3.3 by 3.3 arcminutes.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1152a/

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The Eagle Nebula

Messier 16 (M16), also known as the Eagle Nebula, is located in the southern constellation of Serpens (the Snake).

Using the infrared multi-mode ISAAC instrument on the 8.2-m VLT ANTU telescope, European astronomers were able to image the Eagle Nebula at near-infrared wavelength. The ISAAC near-infrared images cover a 9 x 9 arcminutes region, in three broad-band colours and with sufficient sensitivity to detect young stars of all masses and — most importantly — with an image sharpness as good as 0.35 arcseconds.

The wide-field view of M16 shows that there is much happening in the region. The first impression one gets is of an enormous number of stars. Those which are blue in the infrared image are either members of the young NGC 6611 cluster — whose massive stars are concentrated in the upper right (north west) part of the field — or foreground stars which happen to lie along the line of sight towards M16.

Most of the stars are fainter and more yellow. They are ordinary stars behind M16, along the line of sight through the galactic bulge, and are seen through the molecular clouds out of which NGC 6611 formed. Some very red stars are also seen: these are either very young and embedded in gas and dust clouds, or just brighter stars in the background shining through them.

This photo is the result of a three-colour composite mosaic image of the Eagle Nebula (Messier 16), based on 144 individual images obtained with the infrared multi-mode instrument ISAAC on the ESO Very Large Telescope (VLT) at the Paranal Observatory. At the centre, the so-called "Pillars of Creation" can be seen. This wide-field infrared image shows not only the central three pillars but also several others in the same star-forming region, as well as a huge number of stars in front of, in, or behind the Eagle Nebula. The cluster of bright blue stars to the upper right is NGC 6611, home to the massive and hot stars that illuminate the pillars.

Image Credit: ESO/M.McCaughrean & M.Andersen (AIP)
Explanation from: https://www.eso.org/public/images/eso0142a/

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Hurricane Irma seen by NOAA's GOES East satellite

NOAA's GOES East satellite captured this infrared image of Hurricane Irma in the Bahamas on September 8 at 4:45 a.m. EDT.

Image Credit: NASA/NOAA GOES Project

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Spiral Galaxy NGC 4634

The NASA/ESA Hubble Space Telescope has produced a sharp image of NGC 4634, a spiral galaxy seen exactly side-on. Its disc is slightly warped by ongoing interactions with a nearby galaxy, and it is crisscrossed by clearly defined dust lanes and bright nebulae.

NGC 4634, which lies around 70 million light-years from Earth in the constellation of Coma Berenices, is one of a pair of interacting galaxies. Its neighbour, NGC 4633, lies just outside the upper right corner of the frame, and is visible in wide-field views of the galaxy. While it may be out of sight, it is not out of mind: its subtle effects on NGC 4634 are easy to see to a well-trained eye.

Gravitational interactions pull the neat spiral forms of galaxies out of shape as they get closer to each other, and the disruption to gas clouds triggers vigorous episodes of star formation. While this galaxy’s spiral pattern is not directly visible thanks to our side-on perspective, its disc is slightly warped, and there is clear evidence of star formation.

Along the full length of the galaxy, and scattered around parts of its halo, are bright pink nebulae. Similar to the Orion Nebula in the Milky Way, these are clouds of gas that are gradually coalescing into stars. The powerful radiation from the stars excites the gas and makes it light up, much like a fluorescent sign. The large number of these star formation regions is a telltale sign of gravitational interaction.

The dark filamentary structures that are scattered along the length of the galaxy are caused by cold interstellar dust blocking some of the starlight.

Hubble’s image is a combination of exposures in visible light produced by Hubble’s Advanced Camera for Surveys and the Wide Field and Planetary Camera 2.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1238a/

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The Tarantula Nebula

About 2,400 massive stars in the center of 30 Doradus are producing intense radiation and powerful winds as they blow off material. Multimillion-degree gas detected in X-rays (blue) by the Chandra X-ray Observatory comes from shock fronts formed by these stellar winds and by supernova explosions. This hot gas carves out gigantic bubbles in the surrounding cooler gas and dust shown here in infrared emission from the Spitzer Space Telescope (orange).

Image Credit: X-ray: NASA/CXC/PSU/L.Townsley et al.; Infrared: NASA/JPL/PSU/L.Townsley et al.
Explanation from: http://www.spitzer.caltech.edu/images/4790-sig11-015-30-Doradus-and-The-Growing-Tarantula-Within

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Hurricane Jose seen by Aqua satellite

On September 7 at 12:45 p.m. EDT (1645 UTC) the Moderate Resolution Imaging Spectroradiometer or MODIS instrument aboard NASA's Aqua satellite captured a visible-light image of Hurricane Jose approaching the Leeward Islands.

Image Credit: NASA Goddard MODIS Rapid Response Team

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Open Star Cluster IRAS 17430-2848

Although this cluster of stars gained its name due to its five brightest stars, it is home to hundreds more. The huge number of massive young stars in the cluster is clearly captured in this NASA/ESA Hubble Space Telescope image.

The cluster is located close to the Arches Cluster and is just 100 light-years from the centre of our galaxy. The cluster’s proximity to the dust at the centre of the galaxy means that much of its visible light is blocked, which helped to keep the cluster unknown until its discovery in 1990, when it was revealed by observations in the infrared. Infrared images of the cluster, like the one shown here, allow us to see through the obscuring dust to the hot stars in the cluster.

The Quintuplet Cluster hosts two extremely rare luminous blue variable stars: the Pistol Star and the lesser known V4650 Sgr. If you were to draw a line horizontally through the centre of this image from left to right, you could see the Pistol Star hovering just above the line about one third of the way along it. The Pistol Star is one of the most luminous known stars in the Milky Way and takes its name from the shape of the Pistol Nebula that it illuminates, but which is not visible in this infrared image. The exact age and future of the Pistol Star are uncertain, but it is expected to end in a supernova or even a hypernova in one to three million years.

The cluster also contains a number of red supergiants. These stars are among the largest in the galaxy and are burning their fuel at an incredible speed, meaning they will have a very short lifetime. Their presence suggests an average cluster age of nearly four million years. At the moment these stars are on the verge of exploding as supernovae. During their spectacular deaths they will release vast amounts of energy which, in turn, will heat the material — dust and gas — between the other stars.

This observation shows the Quintuplet Cluster in the infrared and demonstrates the leap in Hubble’s performance since its 1999 image of same object.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1528a/

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Spiral Galaxy Messier 51

M51 is a spiral galaxy, about 30 million light years away, that is in the process of merging with a smaller galaxy seen to its upper left.

Image Credit: X-ray: NASA/CXC/SAO; Optical: Detlef Hartmann; Infrared: NASA/JPL-Caltech

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Hurricane Irma seen from the International Space Station

The eye of Hurricane Irma is clearly visible from the International Space Station as it orbited over the Category 5 storm on September 5, 2017.

Image Credit: NASA

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Earth seen by DSCOVR Observatory

DSCOVR, 1 million miles from Earth

August 21, 2017

Image Credit: NASA EPIC Team

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Spiral Galaxy NGC 634

The NASA/ESA Hubble Space Telescope is renowned for its breathtaking images and this snapshot of NGC 634 is definitely that — the fine detail and exceptionally perfect spiral structure of the galaxy make it hard to believe that this is a real observation and not an artist’s impression or a screenshot taken straight from Star Wars.

This spiral galaxy was discovered back in the nineteenth century by French astronomer Édouard Jean-Marie Stephan, but in 2008 it became a prime target for observations thanks to the violent demise of a white dwarf star. The type Ia supernova known as SN2008a was spotted in the galaxy and briefly rivalled the brilliance of its entire host galaxy but, despite the energy of the explosion, it can no longer be seen this Hubble image, which was taken around a year and a half later.

White dwarfs are thought to be the endpoint of evolution for stars between 0.07 to 8 solar masses, which equates to 97% of the stars in the Milky Way. However, there are exceptions to the rule; in a binary system it is possible for a white dwarf to accrete material from the companion star and gradually put on weight. Like a person gorging on junk food, the star can eventually grow too full — when it exceeds 1.38 solar masses nuclear reactions ignite that produce enormous amounts of energy and the star explodes as a type Ia supernova.

This picture was created from images taken with the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images through a yellow filter (F555W, coloured blue) have been combined with images through red (F625W, coloured green) and near-infrared (F775W, coloured red) filters. The total exposure times per filter were 3750 s, 3530 s and 2484 s, respectively and the field of view is 2.5 x 1.5 arcminutes.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1122a/

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Emission Nebula N83B

Extremely intense radiation from newly born, ultra-bright stars has blown a glowing spherical bubble in the nebula N83B. A new NASA/ESA Hubble Space Telescope image has helped to decipher the complex interplay of gas and radiation in a star-forming region of a nearby galaxy. The image graphically illustrates just how these massive stars sculpt their environment by generating powerful winds that alter the shape of the parent gaseous nebula. These processes are also seen in our own Milky Way in regions like the Orion Nebula.

Extremely intense radiation from newly born, ultra-bright stars has blown a glowing spherical bubble in the nebula N83B. A new NASA/ESA Hubble Space Telescope image has helped to decipher the complex interplay of gas and radiation in a star-forming region of a nearby galaxy. The image graphically illustrates just how these massive stars sculpt their environment by generating powerful winds that alter the shape of the parent gaseous nebula. These processes are also seen in our own Milky Way in regions like the Orion Nebula.

The Hubble Space Telescope is famous for its contribution to our knowledge about star formation in very distant galaxies. Although most of the stars in the Universe were born several billions of years ago, when the Universe was young, star formation still continues today. This new Hubble image shows a very compact star-forming region in a small part of one of our neighbouring galaxies - the Large Magellanic Cloud. This galaxy lies only 165,000 light-years from our own Milky Way and can easily be seen from the Southern Hemisphere with the naked eye.

Young, massive, ultra-bright stars are seen here just as they are born and emerge from the shelter of their pre-natal molecular cloud. Catching these hefty stars at their birthplace is not as easy as it may seem. Their high mass means that the young stars evolve very rapidly and are hard to find at this critical stage. Furthermore, they spend a good fraction of their youth hidden from view, shrouded by large quantities of dust in a molecular cloud. The only chance is to observe them just as they start to emerge from their cocoon - and then often only with very high-resolution telescopes. Astronomers from France, the USA and Germany have used Hubble to study the fascinating interplay between gas, dust and radiation from the newly born stars in this nebula, known as N83B or NGC 1748. Its peculiar and turbulent structure has been revealed for the first time. This high-resolution study has also uncovered several individual stars that are responsible for lighting up this cloud of gas.

The apparently innocuous-looking star at the very centre of the nebula, just below the brightest region, is actually about 30 times more massive and almost 200,000 times brighter than our Sun. The intense light and powerful stellar 'winds' from this ultra-bright star have cleared away the surrounding gas to form a large cavity. The bubble is approximately 25 light-years in diameter - about the same size as the famous star-forming Orion Nebula. The Orion Nebula is sculpted by intense radiation from newly born stars in the same way as N83B. Astronomers estimate that the spherical void in N83B must have been carved out of the nebula very recently - in astronomical terms - maybe as little as 30,000 years ago.

The hottest star in N83B is 45 times more massive than the Sun and is embedded in the brightest region in the nebula. This bright region, situated just above the centre, is only about two light-years across. The region's small size and its intense glow are telltale signs of a very young, massive star. This star is the youngest newcomer to this part of the Large Magellanic Cloud. The Hubble image shows a bright arc structure just below the luminous star. This impressive ridge may have been created in the glowing gas by the hot star's powerful wind.

Measurements of the age of this star and neighbouring stars in the nebula show that they are younger than the nebula's central star. Their formation may have been 'triggered' by the violent wind from the central star. This 'chain-reaction' of stellar births seems to be common in the Universe. About 20 young and luminous stars have been identified in the region, but it may well be that many more massive stars remain undetected in other areas of the Large Magellanic Cloud, hidden by dust in small clusters like N83B.

To the right of the glowing N83B is a much larger diffuse nebula, known as DEM22d, which is partly obscured by an extended lane of dust and gas.

This image is composed of three narrow-band filter images obtained with Hubble's Wide Field Planetary Camera 2 in May 2000. The colours are red (ionised hydrogen, H-alpha), green (ionised oxygen) and blue (ionised hydrogen, H-beta). The blue corresponds to the warmest regions, the red to the coldest. The full image is 66 x 133 arc-seconds, which corresponds to 55 x 108 light-years at the distance of the Large Magellanic Cloud.

Image Credit: ESA, NASA & Mohammad Heydari-Malayeri (Observatoire de Paris, France)
Explanation from: http://spacetelescope.org/news/heic0104/

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Hurricane Irma seen by Suomi NPP satellite

On September 6, 2017, Hurricane Irma—an unusually powerful category 5 storm—slammed into the Leeward Islands on its way toward Puerto Rico and possibly the U.S. mainland.

By definition, category 5 storms deliver maximum sustained winds of at least 157 miles (252 kilometers) per hour. When it hit the Leeward Islands, Irma’s winds surpassed 185 miles (295 kilometers) per hour—making it the strongest storm to ever hit the islands and the strongest storm ever measured for an Atlantic hurricane outside of the Gulf of Mexico or north of the Caribbean.

The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite captured this nighttime view of the storm in the early hours of September 6 as the eye was over the island of Barbuda. The image was acquired by the VIIRS “day-night band,” which detects light in a range of wavelengths from green to near-infrared and uses filtering techniques to observe signals such as city lights, auroras, wildfires, and reflected moonlight. In this case, the clouds were lit by the nearly full Moon. The image is a composite, showing storm imagery combined with VIIRS imagery of city lights.

The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite acquired the second image at 10:35 a.m. local time (14:35 Universal Time) on September 6, 2017. By then, the storm had also hit Anguilla and was poised to strike the Virgin Islands. While damages on Barbuda and Anguilla may not be as severe as feared, the islands of St. Barthelemy and St. Martin experienced extensive damage, according to news reports.

Irma’s winds are not only strong; they spread across a remarkably wide area. Hurricane force winds extend 50 miles (85 km) from the center; tropical-storm-force winds extend up to 185 miles (295 km).

Meteorologists recorded the lowest central pressure (914 millibars) ever for a storm outside of the Gulf of Mexico and western Caribbean. On September 6, Irma had already generated more accumulated cyclone energy—a term meteorologists use to describe the destructive potential of a hurricane based on the strength of its winds and their duration—than the first eight named storms of the Atlantic hurricane season combined, according to Philip Klotzbach of Colorado State University. Irma even broke a record for generating the most accumulated cyclone energy in a 24-hour period.

The latest National Hurricane Center forecast calls for the hurricane to turn west-northwest after grazing Puerto Rico, the Dominican Republic, and Haiti. After that, the potential track area shows Irma’s path will likely move over or near the Turks and Caicos Islands, the Bahamas, and may eventually make landfall on Florida.

Image Credit: NASA Earth Observatory
Explanation from: https://earthobservatory.nasa.gov/NaturalHazards/view.php?id=90912

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X9.3 Solar Flare

An X9.3 class solar flare flashes in the middle of the Sun on September 6, 2017. This image was captured by NASA's Solar Dynamics Observatory at 11:58:20UT and shows light in the 131 angstrom wavelength.

Image Credit: NASA/GSFC/SDO

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Planetary System Gliese 176

A study using data from NASA's Chandra X-ray Observatory and ESA's XMM-Newton suggests X-rays emitted by a planet's host star may provide critical clues to how hospitable a star system could be. Researchers looked at the X-ray brightness from 24 stars with masses similar to the Sun or less, each at least one billion years old. The artist's illustration depicts one of these older Sun-like stars with a planet in orbit around it, which researchers found to be relatively calm compared to younger stars. The large dark area is a "coronal hole", a phenomenon associated with low levels of magnetic activity.

Image Credit: NASA/CXC/M.Weiss
Explanation from: http://chandra.harvard.edu/photo/2017/gj176/more.html

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Hurricane Irma seen by NOAA’s GOES East satellite

This visible light image of Hurricane Irma was captured by NOAA's GOES East satellite as it strengthened to a Category 5 hurricane in the Central Atlantic Ocean on September 5 at 7:45 a.m. EDT (1145 UTC).

Image Credit: NASA/NOAA GOES Project

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Millions of Distant Galaxies

Anyone who has wondered what it might be like to dive into a pool of millions of distant galaxies of different shapes and colours, will enjoy the latest image released by ESO. Obtained in part with the Very Large Telescope, the image is the deepest ground-based U-band image of the Universe ever obtained. It contains more than 27 million pixels and is the result of 55 hours of observations with the VIMOS instrument.

This uniquely beautiful patchwork image, with its myriad of brightly coloured galaxies, shows the Chandra Deep Field South (CDF-S), arguably the most observed and best studied region in the entire sky. The CDF-S is one of the two regions selected as part of the Great Observatories Origins Deep Survey (GOODS), an effort of the worldwide astronomical community that unites the deepest observations from ground- and space-based facilities at all wavelengths from X-ray to radio. Its primary purpose is to provide astronomers with the most sensitive census of the distant Universe to assist in their study of the formation and evolution of galaxies.

The new image released by ESO combines data obtained with the VIMOS instrument in the U- and R-bands, as well as data obtained in the B-band with the Wide-Field Imager (WFI) attached to the 2.2 m MPG/ESO telescope at La Silla, in the framework of the GABODS survey.

The newly released U-band image – the result of 40 hours of staring at the same region of the sky and just made ready by the GOODS team – is the deepest image ever taken from the ground in this wavelength domain. At these depths, the sky is almost completely covered by galaxies, each one, like our own galaxy, the Milky Way, home of hundreds of billions of stars.

Galaxies were detected that are a billion times fainter than the unaided eye can see and over a range of colours not directly observable by the eye. This deep image has been essential to the discovery of a large number of new galaxies that are so far away that they are seen as they were when the Universe was only 2 billion years old.

In this sea of galaxies – or island universes as they are sometimes called – only a very few stars belonging to the Milky Way are seen. One of them is so close that it moves very fast on the sky. This "high proper motion star" is visible to the left of the second brightest star in the image. It appears as a funny elongated rainbow because the star moved while the data were being taken in the different filters over several years.

Image Credit: ESO/ Mario Nonino, Piero Rosati and the ESO GOODS Team
Explanation from: https://www.eso.org/public/news/eso0839/

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NASA’s SDO Captures Image of Mid-level Flare

The Sun emitted a mid-level solar flare, peaking at 4:33 pm EDT on September 4, 2017. NASA’s Solar Dynamics Observatory, which watches the Sun constantly, captured an image of the event. Solar flares are powerful bursts of radiation. Harmful radiation from a flare cannot pass through Earth's atmosphere to physically affect humans on the ground, however — when intense enough — they can disturb the atmosphere in the layer where GPS and communications signals travel.

This flare is classified as an M5.5 class flare. M-class flares are a tenth the size of the most intense flares, the X-class flares. The number provides more information about its strength. An M2 is twice as intense as an M1, an M3 is three times as intense, etc.

Image Credit: NASA/SDO
Explanation from: https://www.nasa.gov/feature/goddard/2017/nasa-s-sdo-captures-image-of-mid-level-flare

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Hurricane Irma

On September 4 at 17:24 UTC, NASA-NOAA's Suomi NPP satellite captured this view of Hurricane Irma as a Category 4 hurricane approaching the Leeward Islands.

Image Credit: NOAA/NASA Goddard MODIS Rapid Response Team

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Spiral Galaxy Messier 81

M81 is a spiral galaxy about 12 million light years away that is both relatively large in the sky and bright, making it a frequent target for both amateur and professional astronomers.

Image Credit: X-ray: NASA/CXC/SAO; Optical: Detlef Hartmann; Infrared: NASA/JPL-Caltech

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Star-Forming Region NGC 604 in the Triangulum Galaxy

A billowing cloud of hydrogen in the Triangulum galaxy (Messier 33), about 2.7 million light-years away from Earth, glows with the energy released by hundreds of young, bright stars. This NASA/ESA Hubble Spare Telescope image provides the sharpest view of NGC 604 so far obtained.

Some 1500 light-years across, this is one of the largest, brightest concentrations of ionised hydrogen (H II) in our local group of galaxies, and is a major centre of star formation.

The gas in NGC 604, around nine tenths of it hydrogen, is gradually collapsing under the force of gravity to create new stars. Once these stars have formed, the vigorous ultraviolet radiation they emit excites the remaining gas in the cloud, making it glow a distinct shade of red. This colour is typical not only of NGC 604 but of other H II regions too. Although it is part of Messier 33 this object is so bright and prominent that it was given its own NGC number.

The fierce ultraviolet radiation released by the stars that give these hydrogen clouds their distinctive glow is also the cause of their uneven appearance and eventual disappearance. The radiation and winds blowing from the surface of these stars gradually erode the cloud they formed from, causing the gases to slowly disperse. The complex structure of NGC 604, with irregular bubbles and wispy filament-like structures alongside denser, redder areas is due to the same forces that will eventually make the cloud disappear. The blister-like cavities show areas of stronger erosion of the cloud. While these areas appear dark in this photograph, they shine brightly at X-ray wavelengths.

This image was created from images taken using the High Resolution Channel of Hubble's Advanced Camera for Surveys. It is a composite of images taken through a total of seven different filters spanning a huge range of wavelengths — from 220 nm in the ultraviolet all the way up to the near infrared at one micron. The field of view is about 31 by 22 arcseconds.

Image Credit: https://www.spacetelescope.org/images/potw1019a/
Explanation from: https://www.spacetelescope.org/images/potw1019a/

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Solar Eclipse seen by DSCOVR Observatory

DSCOVR, 1 million miles from Earth

August 21, 2017

Image Credit: NASA EPIC Team

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Spiral Galaxy NGC 5559

Like firecrackers lighting up the sky on New Year’s Eve, the majestic spiral arms of NGC 5559 are alight with new stars being born. NGC 5559 is a spiral galaxy, with spiral arms filled with gas and dust sweeping out around the bright galactic bulge. These arms are a rich environment for star formation, dotted with a festive array of colours including the newborn stars glowing blue as a result of their immensely high temperatures.

NGC 5559 was discovered by astronomer William Herschel in 1785 and lies approximately 240 million light-years away in the northern constellation of Boötes (the herdsman)

In 2001, a calcium-rich supernova called 2001co was observed in NGC 5559. Calcium-rich supernovae (Ca-rich SNe) are described as “fast-and-faint”, as they're less luminous than other types of supernovae and also evolve more rapidly, to reveal spectra dominated by strong calcium lines. 2001co occurred within the disc of NGC 5559 near star-forming regions, but Ca-rich SNe are often observed at large distances from the nearest galaxy, raising curious questions about their progenitors.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1736a/

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