Pavlof Volcano Eruption seen from the International Space Station

Astronauts aboard the International Space Station (ISS) photographed this striking view of Pavlof Volcano on May 18, 2013. The oblique perspective from the ISS reveals the three dimensional structure of the ash plume, which is often obscured by the top-down view of most remote sensing satellites.

Situated in the Aleutian Arc about 625 miles (1,000 kilometers) southwest of Anchorage, Pavlof began erupting on May 13, 2013. The volcano jetted lava into the air and spewed an ash cloud 20,000 feet (6,000 meters) high. When picture was taken, the space station was about 475 miles south-southeast of the volcano (49.1° North latitude, 157.4° West longitude). The volcanic plume extended southeastward over the North Pacific Ocean

Image Credit: NASA
Explanation from: http://www.nasa.gov/multimedia/imagegallery/image_feature_2515.html

The NGC 3621 Galaxy

This image, from ESO’s Very Large Telescope (VLT), shows a truly remarkable galaxy known as NGC 3621. To begin with, it is a pure-disc galaxy. Like other spirals, it has a flat disc permeated by dark lanes of material and with prominent spiral arms where young stars are forming in clusters (the blue dots seen in the image). But while most spiral galaxies have a central bulge — a large group of old stars packed in a compact, spheroidal region — NGC 3621 doesn’t. In this image, it is clear that there is simply a brightening to the centre, but no actual bulge like the one in NGC 6744, for example.

NGC 3621 is also interesting as it is believed to have an active supermassive black hole at its centre that is engulfing matter and producing radiation. This is somewhat unusual because most of these so-called active galactic nuclei exist in galaxies with prominent bulges. In this particular case, the supermassive black hole is thought to have a relatively small mass, of around 20 000 times that of the Sun.

Another interesting feature is that there are also thought to be two smaller black holes, with masses of a few thousand times that of the Sun, near the nucleus of the galaxy. Therefore, NGC 3621 is an extremely interesting object which, despite not having a central bulge, has a system of three black holes in its central region.

This galaxy is located in the constellation of Hydra (The Sea Snake) and can be seen with a moderate-sized telescope. This image, taken using B, V, and I filters with the FORS1 instrument on the powerful VLT, shows striking detail in this odd object and also reveals a multitude of background galaxies. A number of bright foreground stars that belong to our own Milky Way are also visible.

Image Credit: ESO
Explanation from: https://www.eso.org/public/images/potw1148a/

Stars in NGC 1569

This NASA/ESA Hubble Space Telescope image reveals the iridescent interior of one of the most active galaxies in our local neighbourhood — NGC 1569, a small galaxy located about eleven million light-years away in the constellation of Camelopardalis (The Giraffe).

This galaxy is currently a hotbed of vigorous star formation. NGC 1569 is a starburst galaxy, meaning that — as the name suggests — it is bursting at the seams with stars, and is currently producing them at a rate far higher than that observed in most other galaxies. For almost 100 million years, NGC 1569 has pumped out stars over 100 times faster than the Milky Way!

As a result, this glittering galaxy is home to super star clusters, three of which are visible in this image — one of the two bright clusters is actually the superposition of two massive clusters. Each containing more than a million stars, these brilliant blue clusters reside within a large cavity of gas carved out by multiple supernovae, the energetic remnants of massive stars.

In 2008, Hubble observed the galaxy's cluttered core and sparsely populated outer fringes. By pinpointing individual red giant stars, Hubble’s Advanced Camera for Surveys enabled astronomers to calculate a new — and much more precise — estimate for NGC 1569’s distance. This revealed that the galaxy is actually one and a half times further away than previously thought, and a member of the IC 342 galaxy group.

Astronomers suspect that the IC 342 cosmic congregation is responsible for the star-forming frenzy observed in NGC 1569. Gravitational interactions between this galactic group are believed to be compressing the gas within NGC 1569. As it is compressed, the gas collapses, heats up and forms new stars.

Image Credit: ESA/Hubble & NASA, Aloisi, Ford, Judy Schmidt
Explanation from: https://www.spacetelescope.org/images/potw1626a/

Earth and Moon seen from Mars by Mars Global Surveyor spacecraft

This is the first image of Earth ever taken from another planet that actually shows our home as a planetary disk. Because Earth and the Moon are closer to the Sun than Mars, they exhibit phases, just as the Moon, Venus, and Mercury do when viewed from Earth. As seen from Mars by the NASA Mars Global Surveyor on May 8, 2003, at 13:00 GMT (6:00 a.m. PDT), Earth and the Moon appeared in the evening sky. This Earth/Moon image has been specially processed to allow both Earth (with an apparent magnitude of -2.5) and the much darker Moon (with an apparent magnitude of +0.9) to be visible together. The bright area at the top of the image of Earth is cloud cover over central and eastern North America. Below that, a darker area includes Central America and the Gulf of Mexico. The bright feature near the center right of the crescent Earth consists of clouds over northern South America. The image also shows the Earth-facing hemisphere of the Moon, since the Moon was on the far side of Earth as viewed from Mars. The slightly lighter tone of the lower portion of the image of the Moon results from the large and conspicuous ray system associated with the crater Tycho.

Image Credit: NASA/JPL/Malin Space Science Systems
Explanation from: http://earthobservatory.nasa.gov/IOTD/view.php?id=3481

Supernova Remnant N49

This beautiful composite image shows N49, the aftermath of a supernova explosion in the Large Magellanic Cloud. A new long observation from NASA's Chandra X-ray Observatory, shown in blue, reveals evidence for a bullet-shaped object being blown out of a debris field left over from an exploded star.

In order to detect this bullet, a team of researchers led by Sangwook Park of Penn State University used Chandra to observe N49 for over 30 hours. This bullet can be seen in the bottom right hand corner of the image (roll your mouse over the image above or click here) and is rich in silicon, sulphur and neon. The detection of this bullet shows that the explosion that destroyed the star was highly asymmetric.

The bullet is traveling at a high speed of about 5 million miles an hour away from a bright point source in the upper left part of N49. This bright source may be a so-called soft gamma ray repeater (SGR), a source that emits bursts of gamma rays and X-rays. A leading explanation for these objects is that they are neutron stars with extremely powerful magnetic fields. Since neutron stars are often created in supernova explosions, an association between SGRs and supernova remnants is not unexpected. This case is strengthened by the apparent alignment between the bullet's path and the bright X-ray source. However, the new Chandra data also shows that the bright source is more obscured by gas than expected if it really lies inside the supernova remnant. In other words, it is possible that the bright X-ray source actually lies beyond the remnant and is projected along the line of sight. Another possible bullet is located on the opposite side of the remnant, but it is harder to see in the image because it overlaps with the bright emission - described below - from the shock-cloud interaction.

Optical data from the Hubble Space Telescope (yellow and purple) shows bright filaments where the shock wave generated by the supernova is interacting with the densest regions in nearby clouds of cool, molecular gas.

Using the new Chandra data, the age of N49 -- as it appears in the image -- is thought to be about 5,000 years and the energy of the explosion is estimated to be about twice that of an average supernova. These preliminary results suggest that the original explosion was caused by the collapse of a massive star.

Image Credit: X-ray: (NASA/CXC/Penn State/S.Park et al.); Optical: NASA/STScI/UIUC/Y.H.Chu & R.Williams et al
Explanation from: http://chandra.si.edu/photo/2010/n49/

Saturn

With giant Saturn hanging in the blackness and sheltering Cassini from the Sun's blinding glare, the spacecraft viewed the rings as never before, revealing previously unknown faint rings and even glimpsing its home world.

This marvelous panoramic view was created by combining a total of 165 images taken by the Cassini wide-angle camera over nearly three hours on September 15, 2006. The full mosaic consists of three rows of nine wide-angle camera footprints; only a portion of the full mosaic is shown here. Color in the view was created by digitally compositing ultraviolet, infrared and clear filter images and was then adjusted to resemble natural color.

The mosaic images were acquired as the spacecraft drifted in the darkness of Saturn's shadow for about 12 hours, allowing a multitude of unique observations of the microscopic particles that compose Saturn's faint rings.

Ring structures containing these tiny particles brighten substantially at high phase angles: i.e., viewing angles where the sun is almost directly behind the objects being imaged.

Image Credit: NASA/JPL/Space Science Institute
Explanation from: https://www.nasa.gov/mission_pages/cassini/multimedia/gallery/pia08329.html

The Omega Nebula

The region of the nebula shown in this picture is about 3500 times wider than our Solar System. The area also represents about 60 percent of the total view captured by ACS. The nebula resides 5500 light-years away in the constellation Sagittarius.

Like its famous cousin in Orion, the Swan Nebula is illuminated by ultraviolet radiation from young, massive stars - each about six times hotter and 30 times more massive than the Sun - located just beyond the upper right corner of the image. The powerful radiation from these stars evaporates and erodes the dense cloud of cold gas within which the stars formed. The blistered walls of the hollow cloud shine primarily in the blue, green, and red light emitted by excited atoms of hydrogen, nitrogen, oxygen, and sulphur. Particularly striking is the rose-like feature, seen to the right of centre, which glows in the red light emitted by hydrogen and sulphur.

As the infant stars evaporate the surrounding cloud, they expose dense pockets of gas that may contain developing stars. Because these dense pockets are more resistant to the withering radiation than the surrounding cloud, they appear as sculptures in the walls of the cloud or as isolated islands in a sea of glowing gas. One isolated pocket is seen at the centre of the brightest region of the nebula and is about 10 times larger than our Solar System. Other dense pockets of gas have formed the remarkable feature jutting inward from the left edge of the image, which resembles the famous Horsehead Nebula in Orion.

The ACS made this observation on 1 and 2 April 2002. The colour image is constructed from four separate images taken in these filters: blue, near infrared, hydrogen alpha, and doubly ionised oxygen.

Image Credit: NASA, Holland Ford (JHU), the ACS Science Team and ESA
Explanation from: https://www.spacetelescope.org/images/heic0206d/

Center of the Milky Way Galaxy in the Infrared

The Spitzer Space Telescope's infrared-light observations provide a detailed and spectacular view of the galactic center region. The swirling core of our galaxy harbors hundreds of thousands of stars that cannot be seen in visible light. These stars heat the nearby gas and dust. These dusty clouds glow in infrared light and reveal their often dramatic shapes. Some of these clouds harbor stellar nurseries that are forming new generations of stars. Like the downtown of a large city, the center of our galaxy is a crowded, active, and vibrant place.

Image Credit: NASA/JPL-Caltech/SSC/S.Stolovy
Explanation from: http://chandra.si.edu/photo/2009/galactic/more.html

Artist's impression of the Supernova 1993J

Observations with the Hubble Space Telescope allow a look into a supernova explosion under development. In this artist's view the red supergiant supernova progenitor star (left) is exploding after having transferred about 10 solar masses of hydrogen gas to the blue companion star (right). This interaction process happened over about 250 years and affected the supernova explosion to such an extent that SN 1993J was later known as one of the most peculiar supernovae ever seen.

Image Credit: ESA and Justyn R. Maund
Explanation from: https://www.spacetelescope.org/images/heic0401a/

The Omega Nebula in Infrared

NASA's Spitzer Space Telescope has captured infrared view of the choppy star-making cloud called M17, also known as the Omega Nebula or the Swan Nebula.

The cloud, located about 6,000 light-years away in the constellation Sagittarius, is dominated by a central group of massive stars -- the most massive stars in the region. These central stars give off intense flows of expanding gas, which rush like rivers against dense piles of material, carving out the deep pocket at center of the picture. Winds from the region's other massive stars push back against these oncoming rivers, creating bow shocks like those that pile up in front of speeding boats.

Three of these bow shocks are nestled in the upper left side of the central cavity, but are difficult to spot in this view. They are composed of compressed gas in addition to dust that glows at infrared wavelengths Spitzer can see. The smiley-shaped bow shocks curve away from the stellar winds of the central massive stars.

This picture was taken with Spitzer's infrared array camera. It is a four-color composite, in which light with a wavelength of 3.6 microns is blue; 4.5-micron light is green; 5.8-micron light is orange; and 8-micron light is red. Dust is red, hot gas is green and white is where gas and dust intermingle. Foreground and background stars appear scattered through the image.

Image Credit: NASA/JPL-Caltech/M. Povich (Univ. of Wisconsin)
Explanation from: http://www.spitzer.caltech.edu/images/1972-ssc2008-21a1-M17-Celestial-Sea-of-Stars

Planetary Nebula NGC 6565

A dying star’s final moments are captured in this image from the NASA/ESA Hubble Space Telescope. The death throes of this star may only last mere moments on a cosmological timescale, but this star’s demise is still quite lengthy by our standards, lasting tens of thousands of years!

The star’s agony has culminated in a wonderful planetary nebula known as NGC 6565, a cloud of gas that was ejected from the star after strong stellar winds pushed the star’s outer layers away into space. Once enough material was ejected, the star’s luminous core was exposed and it began to produce ultraviolet radiation, exciting the surrounding gas to varying degrees and causing it to radiate in an attractive array of colours. These same colours can be seen in the famous and impressive Ring Nebula, a prominent example of a nebula like this one.

Planetary nebulae are illuminated for around 10 000 years before the central star begins to cool and shrink to become a white dwarf. When this happens, the star’s light drastically diminishes and ceases to excite the surrounding gas, so the nebula fades from view.

Image Credit: ESA/Hubble, NASA, M. Novak
Explanation from: https://www.spacetelescope.org/images/potw1530a/

Bright 'Evening Star' seen from Mars is Earth

This view of the twilight sky and Martian horizon taken by NASA's Curiosity Mars rover includes Earth as the brightest point of light in the night sky. Earth is a little left of center in the image, and our moon is just below Earth.

Researchers used the left eye camera of Curiosity's Mast Camera (Mastcam) to capture this scene about 80 minutes after sunset on the 529th Martian day, or sol, of the rover's work on Mars (Januar 31, 2014). The image has been processed to remove effects of cosmic rays.

A human observer with normal vision, if standing on Mars, could easily see Earth and the Moon as two distinct, bright "evening stars."

The distance between Earth and Mars when Curiosity took the photo was about 99 million miles (160 million kilometers).

Image Credit: NASA/JPL-Caltech/MSSS/TAMU
Explanation from: http://photojournal.jpl.nasa.gov/catalog/PIA17936

Planetary Nebula Henize 3-401

This image, taken with the NASA/ESA Hubble Space Telescope, shows the young planetary nebula Henize 3-401. Hubble's extraordinary vision reveals that it is one of the most elongated planetary nebulae found so far. The image shows two very long cylindrical outflows with intricate thread-like structures and tattered ends. We are seeing the central star responsible for the beautiful display for the first time in this image. Henize 3-401 is located in the constellation of Carina (the Keel) at an approximate distance of 10 000 light-years. This picture is composed of three exposures obtained with Hubble's Wide Field Planetary Camera 2 on 12 June 1997. The three exposures were taken through a wide orange filter (1200 seconds) shown in blue, a hydrogen-alpha filter (400 seconds) shown in red, and a singly ionised sulphur filter (1200 seconds) shown in green.

Image Credit: European Space Agency and Pedro Garcma-Lario (ESA ISO Data Centre)
Explanation from: https://www.spacetelescope.org/images/heic0209a/

Tarantula Nebula in the Infrared

This Hubble image shows a cosmic creepy-crawly known as the Tarantula Nebula in infrared light. This region is full of star clusters, glowing gas, and thick dark dust.

Created using observations taken as part of the Hubble Tarantula Treasury Project (HTTP), this image was snapped using Hubble's Wide Field Camera 3 (WFC3) and Advanced Camera for Surveys (ACS). The Hubble Tarantula Treasury Project (HTTP) is scanning and imaging many of the many millions of stars within the Tarantula, mapping out the locations and properties of the nebula's stellar inhabitants. These observations will help astronomers to piece together an understanding of the nebula's skeleton, viewing its starry structure.

Image Credit: NASA, ESA, E. Sabbi (STScI)
Explanation from: https://www.spacetelescope.org/images/heic1402a/

Earth and Moon seen by Mars Reconnaissance Orbiter from 142 million kilometers away

The High Resolution Imaging Science Experiment (HiRISE) camera would make a great backyard telescope for viewing Mars, and we can also use it at Mars to view other planets. This is an image of Earth and the Moon, acquired on October 3, 2007, by the HiRISE camera on NASA's Mars Reconnaissance Orbiter.

At the time the image was taken, Earth was 142 million kilometers (88 million miles) from Mars, giving the HiRISE image a scale of 142 kilometers (88 miles) per pixel, an Earth diameter of about 90 pixels and a Moon diameter of 24 pixels. The phase angle is 98 degrees, which means that less than half of the disk of the Earth and the disk of the Moon have direct illumination. We could image Earth and Moon at full disk illumination only when they are on the opposite side of the sun from Mars, but then the range would be much greater and the image would show less detail.

On the Earth image we can make out the west coast outline of South America at lower right, although the clouds are the dominant features. These clouds are so bright, compared with the Moon, that they are saturated in the HiRISE images. In fact the red-filter image was almost completely saturated, the Blue-Green image had significant saturation, and the brightest clouds were saturated in the infrared image. This color image required a fair amount of processing to make a nice-looking release. The Moon image is unsaturated but brightened relative to Earth for this composite. The lunar images are useful for calibration of the camera.

Image Credit: NASA/JPL-Caltech
Explanation from: http://photojournal.jpl.nasa.gov/catalog/PIA10244

Giant Twisters in the Lagoon Nebula

This Hubble Telescope snapshot unveils a pair of one-half, light-year-long interstellar "twisters" - eerie funnels and twisted-rope structures (upper left) - in the heart of the Lagoon Nebula (M8) which lies 5,000 light-years from Earth in the direction of the constellation Sagittarius.

The hot, central star, O Herschel 36 (upper left), is the primary source of the illuminating light for the brightest region in the nebula, called the Hourglass. The glare from this hot star is eroding the clouds by heating the hydrogen gas in them, seen as a blue mist at the right of the image. This activity drives away violent stellar winds that are tearing into the cool clouds.

Image Credit: NASA/A. Caulet (ST-ECF, ESA)
Explanation from: https://www.nasa.gov/multimedia/imagegallery/image_feature_1181.html

The planetary nebula ESO 378-1

This extraordinary bubble, glowing like the ghost of a star in the haunting darkness of space, may appear supernatural and mysterious, but it is a familiar astronomical object: a planetary nebula, the remnants of a dying star. This is the best view of the little-known object ESO 378-1 yet obtained and was captured by ESO’s Very Large Telescope in northern Chile.

Image Credit: ESO
Explanation from: http://www.eso.org/public/images/eso1532a/

Supernova Remnant E0102

This image of the debris of an exploded star - known as supernova remnant 1E 0102.2-7219, or "E0102" for short - features data from NASA's Chandra X-ray Observatory. E0102 is located about 190,000 light years away in the Small Magellanic Cloud, one of the nearest galaxies to the Milky Way. It was created when a star that was much more massive than the Sun exploded, an event that would have been visible from the Southern Hemisphere of the Earth over 1000 years ago.

Chandra first observed E0102 shortly after its launch in 1999. New X-ray data have now been used to create this spectacular image and help celebrate the ten-year anniversary of Chandra's launch on July 23, 1999. In this latest image of E0102, the lowest-energy X-rays are colored orange, the intermediate range of X-rays is cyan, and the highest-energy X-rays Chandra detected are blue. An optical image from the Hubble Space Telescope (in red, green and blue) shows additional structure in the remnant and also reveals foreground stars in the field.

The Chandra image shows the outer blast wave produced by the supernova (blue), and an inner ring of cooler (red-orange) material. This inner ring is probably expanding ejecta from the explosion that is being heated by a shock wave traveling backwards into the ejecta. A massive star (not visible in this image) is illuminating the green cloud of gas and dust to the lower right of the image. This star may have similar properties to the one that exploded to form E0102.

Analysis of the Chandra spectrum gives astronomers new information about the geometry of the remnant, with implications for the nature of the explosion. The spectrum - which precisely separates X-rays of different energies - shows some material is moving away from Earth and some is moving toward us. When the material is moving away, its light is shifted toward the red end of the spectrum due to the so-called Doppler effect. Alternatively, when material is moving toward us, the light is bluer because of the same effect.

Image Credit: X-ray (NASA/CXC/MIT/D.Dewey et al. & NASA/CXC/SAO/J.DePasquale); Optical (NASA/STScI)
Explanation from: http://chandra.si.edu/photo/2009/e0102/

Dwarf Galaxy PGC 51017

The bright streak of glowing gas and stars in this NASA/ESA Hubble Space Telescope image is known as PGC 51017, or SBSG 1415+437. It is type of galaxy known as a blue compact dwarf.

This particular dwarf is well studied and has an interesting star formation history. Astronomers initially thought that SBS 1415+437 was a very young galaxy currently undergoing its very first burst of star formation, but more recent studies have suggested that the galaxy is in fact a little older, containing stars over 1.3 billion years old.

Starbursts are an area of ongoing research for astronomers — short-lived and intense periods of star formation, during which huge amounts of gas within a galaxy are hungrily used up to form newborn stars.

They have been seen in gas-rich disc galaxies, and in some lower-mass dwarfs. However, it is still unclear whether all dwarf galaxies experience starbursts as part of their evolution. It is possible that dwarf galaxies undergo a star formation cycle, with bursts occurring repeatedly over time.

SBS 1415+437 is an interesting target for another reason. Dwarf galaxies like this are thought to have formed early in the Universe, producing some of the very first stars before merging together to create more massive galaxies. Dwarf galaxies which contain very few of the heavier elements formed from having several generations of stars, like SBS 1415+437, remain some of the best places to study star-forming processes similar to those thought to occur in the early Universe. However, it seems that our nearby patch of the Universe may not contain any galaxies that are currently undergoing their first burst of star formation.

Image Credit: ESA/Hubble, NASA, Alessandra Aloisi (STScI) and Nick Rose
Explanation from: https://www.spacetelescope.org/images/potw1511a/

Artist's Impression of the Supernova 1993J

This is an artist's impression of supernova 1993J, an exploding star in the galaxy M81. The supernova originated in a double-star system where one member was a massive star that exploded after siphoning most of its hydrogen envelope to its companion star. After two decades, astronomers have at last identified the blue helium-burning companion star, seen at the center of the expanding nebula of debris from the supernova. The NASA/ESA Hubble Space Telescope identified the ultraviolet glow of the surviving companion embedded in the fading glow of the supernova.

Image Credit: NASA, ESA, and G. Bacon (STScI)
Explanation from: https://www.spacetelescope.org/images/opo1438a/