Mount Etna, Sicily, Italy
December 3, 2015
Image Credit: Marco Restivo/Demotix/Corbis
December 24, 2016
Aurora over Laksvatn Fjord
Laksvatn Fjord, Laksvatn, Troms, Norway
February 2016
Image Credit & Copyright: Matt Walford
The Black Eye Galaxy (Messier 64)
A collision of two galaxies has left a merged star system with an unusual appearance as well as bizarre internal motions. Messier 64 (M64) has a spectacular dark band of absorbing dust in front of the galaxy's bright nucleus, giving rise to its nicknames of the "Black Eye" or "Evil Eye" galaxy.
Fine details of the dark band are revealed in this image of the central portion of M64 obtained with the Hubble Space Telescope. M64 is well known among amateur astronomers because of its appearance in small telescopes. It was first cataloged in the 18th century by the French astronomer Messier. Located in the northern constellation Coma Berenices, M64 resides roughly 17 million light-years from Earth.
Image Credit: NASA/ESA and The Hubble Heritage Team (AURA/STScI)
Explanation from: http://www.spacetelescope.org/images/opo0404a/
Star-Forming Region NGC 1999
This image from the Atacama Pathfinder Experiment (APEX) telescope in Chile shows a beautiful view of clouds of cosmic dust in the region of Orion. While these dense interstellar clouds seem dark and obscured in visible-light observations, APEX’s LABOCA camera can detect the heat glow of the dust and reveal the hiding places where new stars are being formed. But one of these dark clouds is not what it seems.
In space, dense clouds of cosmic gas and dust are the birthplaces of new stars. In visible light, this dust is dark and obscuring, hiding the stars behind it. So much so that, when astronomer William Herschel observed one such cloud in the constellation of Scorpius in 1774, he thought it was a region empty of stars and is said to have exclaimed, "Truly there is a hole in the sky here!"
In order to better understand star formation, astronomers need telescopes that can observe at longer wavelengths, such as the submillimetre range, in which the dark dust grains shine rather than absorb light. APEX, on the Chajnantor Plateau in the Chilean Andes, is the largest single-dish submillimetre-wavelength telescope operating in the southern hemisphere, and is ideal for astronomers studying the birth of stars in this way.
Located in the constellation of Orion (The Hunter), 1500 light-years away from Earth, the Orion Molecular Cloud Complex is the closest region of massive star formation to Earth, and contains a treasury of bright nebulae, dark clouds and young stars. The new image shows just part of this vast complex in visible light, with the APEX observations overlaid in brilliant orange tones that seem to set the dark clouds on fire. Often, the glowing knots from APEX correspond to darker patches in visible light — the tell-tale sign of a dense cloud of dust that absorbs visible light, but glows at submillimetre wavelengths, and possibly a site of star formation.
The bright patch below of the centre of the image is the nebula NGC 1999. This region — when seen in visible light — is what astronomers call a reflection nebula, where the pale blue glow of background starlight is reflected from clouds of dust. The nebula is mainly illuminated by the energetic radiation from the young star V380 Orionis lurking at its heart. In the centre of the nebula is a dark patch, which can be seen even more clearly in a well-known image from the NASA/ESA Hubble Space Telescope.
Normally, a dark patch such as this would indicate a dense cloud of cosmic dust, obscuring the stars and nebula behind it. However, in this image we can see that the patch remains strikingly dark, even when the APEX observations are included. Thanks to these APEX observations, combined with infrared observations from other telescopes, astronomers believe that the patch is in fact a hole or cavity in the nebula, excavated by material flowing out of the star V380 Orionis. For once, it truly is a hole in the sky!
The region in this image is located about two degrees south of the large and well-known Orion Nebula (Messier 42), which can be seen at the top edge of the wider view in visible light from the Digitized Sky Survey.
Explanation from: https://www.eso.org/public/news/eso1304/
December 23, 2016
Herbig–Haro object 24
This image shows the Herbig–Haro object 24 and the surrounding sky as it is seen from the ground.
Image Credit: NASA, ESA, Digitized Sky Survey 2, Davide De Martin
Spiral Galaxy NGC 986
This Hubble image is a snapshot of NGC 986 — a barred spiral galaxy discovered in 1828 by James Dunlop. This close-up view of the galaxy was captured by Hubble’s Wide Field and Planetary Camera 2 (WFPC2).
NGC 986 is found in the constellation of Fornax (The Furnace), located in the southern sky. NGC 986 is a bright, 11th-magnitude galaxy sitting around 56 million light-years away, and its golden centre and barred swirling arms are clearly visible in this image.
Barred spiral galaxies are spiral galaxies with a central bar-shaped structure composed of stars. NGC 986 has the characteristic S-shaped structure of this type of galactic morphology. Young blue stars can be seen dotted amongst the galaxy’s arms and the core of the galaxy is also aglow with star formation.
To the top right of this image the stars appear a little fuzzy. This is because a gap in the Hubble data was filled in with data from ground-based telescopes. Although the view we see in this filled in patch is accurate, the resolution of the stars is no match for Hubble’s clear depiction of the spiral galaxy.
Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1446a/
Coronal Mass Ejection seen by NASA's SOHO
A large coronal mass ejection ejects a cloud of particles into space on 2 December 2003. In this composite an EIT 304 image of the Sun from about the same time has been appropriately scaled and superimposed on a LASCO C2 image where a red occulting disk can be seen extending around the Sun. This LASCO coronagraph instrument allows details in the corona to be observed.
Image Credit: NASA
Sahara Desert and Mediterranean Sea seen from the International Space Station
ISS, Orbit of the Earth
August 2016
Image Credit: NASA/ESA
December 22, 2016
Search for Water in the Universe
The Atacama Large Millimeter/submillimeter Array (ALMA) in Chile has begun observing in a new range of the electromagnetic spectrum. This has been made possible thanks to new receivers installed at the telescope’s antennas, which can detect radio waves with wavelengths from 1.4 to 1.8 millimetres — a range previously untapped by ALMA. This upgrade allows astronomers to detect faint signals of water in the nearby Universe.
ALMA observes radio waves from the Universe, at the low-energy end of the electromagnetic spectrum. With the newly installed Band 5 receivers, ALMA has now opened its eyes to a whole new section of this radio spectrum, creating exciting new observational possibilities.
The European ALMA Programme Scientist, Leonardo Testi, explains the significance: “The new receivers will make it much easier to detect water, a prerequisite for life as we know it, in our Solar System and in more distant regions of our galaxy and beyond. They will also allow ALMA to search for ionised carbon in the primordial Universe.”
It is ALMA’s unique location, 5000 metres up on the barren Chajnantor plateau in Chile, that makes such an observation possible in the first place. As water is also present in Earth’s atmosphere, observatories in less elevated and less arid environments have much more difficulty identifying the origin of the emission coming from space. ALMA’s great sensitivity and high angular resolution mean that even faint signals of water in the local Universe can now be imaged at this wavelength.
The Band 5 receiver, which was developed by the Group for Advanced Receiver Development (GARD) at Onsala Space Observatory, Chalmers University of Technology, Sweden, has already been tested at the APEX telescope in the SEPIA instrument. These observations were also vital to help select suitable targets for the first receiver tests with ALMA.
The first production receivers were built and delivered to ALMA in the first half of 2015 by a consortium consisting of the Netherlands Research School for Astronomy (NOVA) and GARD in partnership with the National Radio Astronomy Observatory (NRAO), which contributed the local oscillator to the project. The receivers are now installed and being prepared for use by the community of astronomers.
To test the newly installed receivers observations were made of several objects including the colliding galaxies Arp 220, a massive region of star formation close to the centre of the Milky Way, and also a dusty red supergiant star approaching the supernova explosion that will end its life.
To process the data and check its quality, astronomers, along with technical specialists from ESO and the European ALMA Regional Centre (ARC) network, gathered at the Onsala Space Observatory in Sweden, for a "Band 5 Busy Week" hosted by the Nordic ARC node. The final results have just been made freely available to the astronomical community worldwide.
Team member Robert Laing at ESO is optimistic about the prospects for ALMA Band 5 observations: “It's very exciting to see these first results from ALMA Band 5 using a limited set of antennas. In the future, the high sensitivity and angular resolution of the full ALMA array will allow us to make detailed studies of water in a wide range of objects including forming and evolved stars, the interstellar medium and regions close to supermassive black holes.”
Image Credit: ALMA(ESO/NAOJ/NRAO)/NASA/ESA and The Hubble Heritage Team (STScI/AURA)
Explanation from: http://www.eso.org/public/news/eso1645/
Spiral Galaxy NGC 7793
This image from the NASA/ESA Hubble Space Telescope shows NGC 7793, a spiral galaxy in the constellation of Sculptor some 13 million light-years away from Earth. NGC 7793 is one of the brightest galaxies in the Sculptor Group, and one of the closest groups of galaxies to the Local Group — the group of galaxies containing our galaxy, the Milky Way and the Magellanic Clouds.
The image shows NGC 7793’s spiral arms and small central bulge. Unlike some other spirals, NGC 7793 doesn’t have a very pronounced spiral structure, and its shape is further muddled by the mottled pattern of dark dust that stretches across the frame. The occasional burst of bright pink can be seen in the galaxy, highlighting stellar nurseries containing newly-forming baby stars.
Although it may look serene and beautiful from our perspective, this galaxy is actually a very dramatic and violent place. Astronomers have discovered a powerful microquasar within NGC 7793 — a system containing a black hole actively feeding on material from a companion star. While many full-sized quasars are known at the cores of other galaxies, it is unusual to find a quasar in a galaxy’s disc rather than at its centre.
Micro-quasars are almost like scale models — they allow astronomers to study quasars in detail. As material falls inwards towards this black hole, it creates a swirling disc around it. Some of the infalling gas is propelled violently outwards at extremely high speeds, creating jets streaking out into space in opposite directions. In the case of NGC 7793, these jets are incredibly powerful, and are in the process of creating an expanding bubble of hot gas some 1000 light-years across.
Image Credit: ESA/Hubble & NASA, D. Calzetti and the LEGUS Team
Explanation from: https://www.spacetelescope.org/images/potw1438a/
Earth and Solar Arrays of the International Space Station
ISS, Orbit of the Earth
September 2016
Image Credit: NASA/ESA
December 21, 2016
MSH 11-62
When X-rays, shown in blue, from Chandra and XMM-Newton are joined in this image with radio data from the Australia Telescope Compact Array (pink) and visible light data from the Digitized Sky Survey (DSS, yellow), a new view of the region emerges. This object, known as MSH 11-62, contains an inner nebula of charged particles that could be an outflow from the dense spinning core left behind when a massive star exploded.
Taurus Molecular Cloud
This image from the APEX (Atacama Pathfinder Experiment) telescope in Chile shows a sinuous filament of cosmic dust more than ten light-years long. In it, newborn stars are hidden, and dense clouds of gas are on the verge of collapsing to form yet more stars. It is one of the regions of star formation closest to us. The cosmic dust grains are so cold that observations at wavelengths of around one millimetre, such as these made with the LABOCA camera on APEX, are needed to detect their faint glow.
The Taurus Molecular Cloud, in the constellation of Taurus (The Bull), lies about 450 light-years from Earth. This image shows two parts of a long, filamentary structure in this cloud, which are known as Barnard 211 and Barnard 213. Their names come from Edward Emerson Barnard’s photographic atlas of the “dark markings of the sky”, compiled in the early 20th century. In visible light, these regions appear as dark lanes, lacking in stars. Barnard correctly argued that this appearance was due to “obscuring matter in space”.
We know today that these dark markings are actually clouds of interstellar gas and dust grains. The dust grains — tiny particles similar to very fine soot and sand — absorb visible light, blocking our view of the rich star field behind the clouds. The Taurus Molecular Cloud is particularly dark at visible wavelengths, as it lacks the massive stars that illuminate the nebulae in other star-formation regions such as Orion. The dust grains themselves also emit a faint heat glow but, as they are extremely cold at around -260 degrees Celsius, their light can only be seen at wavelengths much longer than visible light, around one millimetre.
These clouds of gas and dust are not merely an obstacle for astronomers wishing to observe the stars behind them. In fact, they are themselves the birthplaces of new stars. When the clouds collapse under their own gravity, they fragment into clumps. Within these clumps, dense cores may form, in which the hydrogen gas becomes dense and hot enough to start fusion reactions: a new star is born. The birth of the star is therefore surrounded by a cocoon of dense dust, blocking observations at visible wavelengths. This is why observations at longer wavelengths, such as the millimetre range, are essential for understanding the early stages of star formation.
The upper-right part of the filament shown here is Barnard 211, while the lower-left part is Barnard 213. The millimetre-range observations from the LABOCA camera on APEX, which reveal the heat glow of the cosmic dust grains, are shown here in orange tones, and are superimposed on a visible light image of the region, which shows the rich background of stars. The bright star above the filament is φ Tauri, while the one partially visible at the left-hand edge of the image is HD 27482. Both stars are closer to us than the filament, and are not associated with it.
Observations show that Barnard 213 has already fragmented and formed dense cores — as illustrated by the bright knots of glowing dust — and star formation has already happened. However, Barnard 211 is in an earlier stage of its evolution; the collapse and fragmentation is still taking place, and will lead to star formation in the future. This region is therefore an excellent place for astronomers to study how Barnard’s “dark markings of the sky” play a crucial part in the lifecycle of stars.
The observations were made by Alvaro Hacar (Observatorio Astronómico Nacional-IGN, Madrid, Spain) and collaborators. The LABOCA camera operates on the 12-metre APEX telescope, on the plateau of Chajnantor in the Chilean Andes, at an altitude of 5000 metres. APEX is a pathfinder for the next generation submillimetre telescope, the Atacama Large Millimeter/submillimeter Array (ALMA), which is being built and operated on the same plateau.
Image Credit: ESO/APEX (MPIfR/ESO/OSO)/A. Hacar et al./Digitized Sky Survey 2, Davide De Martin
Explanation from: https://www.eso.org/public/news/eso1209/
Herbig–Haro 34
The artistic outburst of an extremely young star, in the earliest phase of formation, is captured in this spectacular image from the NASA/ESA Hubble Space Telescope. The colourful wisps, found in the lower left of the image, are painted onto the sky by a young star cocooned in the partially illuminated cloud of obscuring dust seen to the upper right.
Pictured punching through the enshrouding dust is an extremely hot, blue jet of gas released by the young star. As this jet speeds through space, it collides with cooler surrounding material. The result is the colourful object to the lower left, produced as the cooler material is heated by the jet.
This wispy object is known as HH34 and it is an example of a Herbig–Haro (HH) object. It resides approximately 1400 light-years away near the Orion Nebula, a large star formation region within the Milky Way. HH objects exist for a cosmically brief time — typically thousands of years — with changes seen in observations taken only a few years apart.
Although the jet extends the entire length between the infant star and HH34, only a fraction of it appears visible. This part of the jet possesses an intricate structure of knots and ripples, thought to be caused by the different outbursts catching up and ramming into each other over time.
Explanation from: https://www.spacetelescope.org/images/potw1551a/
Earth's Atmosphere and Sunrise seen from the International Space Station
ISS, Orbit of the Earth
September 2016
Image Credit: NASA/ESA
December 20, 2016
Saturn's moon Mimas
It may look as though Saturn's moon Mimas is crashing through the rings in this image taken by NASA's Cassini spacecraft, but Mimas is actually 28,000 miles (45,000 kilometers) away from the rings. There is a strong connection between the icy moon and Saturn's rings, though. Gravity links them together and shapes the way they both move.
The gravitational pull of Mimas (246 miles or 396 kilometers across) creates waves in Saturn's rings that are visible in some Cassini images. Mimas' gravity also helps create the Cassini Division (not pictured here), which separates the A and B rings.
This view looks toward the anti-Saturn hemisphere of Mimas. North on Mimas is up and rotated 15 degrees to the right. The image was taken in green light with the Cassini spacecraft narrow-angle camera on October 23, 2016.
The view was acquired at a distance of approximately 114,000 miles (183,000 kilometers) from Mimas and at a Sun-Mimas-spacecraft, or phase, angle of 29 degrees. Image scale is 3,300 feet (1 kilometer) per pixel.
Image Credit: NASA/JPL-Caltech/Space Science Institute
Explanation from: http://photojournal.jpl.nasa.gov/catalog/PIA20510
Star-Forming Region NGC 6357
- NGC 6357 is a region where radiation from hot, young stars is energizing the surrounding gas and dust.
- This composite contains X-ray data from Chandra (purple) plus infrared (orange) and optical data (blue).
- X-rays can penetrate the shrouds of gas and dust surrounding infant stars like those in NGC 6357.
Although there are no seasons in space, this cosmic vista invokes thoughts of a frosty winter landscape. It is, in fact, a region called NGC 6357 where radiation from hot, young stars is energizing the cooler gas in the cloud that surrounds them.
This composite image contains X-ray data from NASA's Chandra X-ray Observatory and the ROSAT telescope (purple), infrared data from NASA's Spitzer Space Telescope (orange), and optical data from the SuperCosmos Sky Survey (blue) made by the United Kingdom Infrared Telescope.
Located in our galaxy about 5,500 light years from Earth, NGC 6357 is actually a "cluster of clusters," containing at least three clusters of young stars, including many hot, massive, luminous stars. The X-rays from Chandra and ROSAT reveal hundreds of point sources, which are the young stars in NGC 6357, as well as diffuse X-ray emission from hot gas. There are bubbles, or cavities, that have been created by radiation and material blowing away from the surfaces of massive stars, plus supernova explosions.
Astronomers call NGC 6357 and other objects like it "HII" (pronounced "H-two") regions. An HII region is created when the radiation from hot, young stars strips away the electrons from neutral hydrogen atoms in the surrounding gas to form clouds of ionized hydrogen, which is denoted scientifically as "HII".
Researchers use Chandra to study NGC 6357 and similar objects because young stars are bright in X-rays. Also, X-rays can penetrate the shrouds of gas and dust surrounding these infant stars, allowing astronomers to see details of star birth that would be otherwise missed.
Image Credit: X-ray: NASA/CXC/PSU/L.Townsley et al; Optical: UKIRT; Infrared: NASA/JPL-Caltech
Explanation from: http://chandra.harvard.edu/photo/2016/ngc6357/
Artist’s impression of the view of the Siding Spring Comet (C/2013 A1) from the surface of Mars
The Siding Spring Comet
C/2013 A1 (Siding Spring) is an Oort cloud comet discovered on 3 January 2013 by Robert H. McNaught at Siding Spring Observatory using the 0.5-meter (20 in) Uppsala Southern Schmidt Telescope.
At the time of discovery it was 7.2 AU from the Sun and located in the constellation Lepus. Comet C/2013 A1 probably took millions of years to come from the Oort cloud. After leaving the planetary region of the Solar System, the post-perihelion orbital period (epoch 2050) is estimated to be roughly 1 million years.
C/2013 A1 passed the planet Mars very closely on 19 October 2014. After its discovery, there was thought to be a chance of a collision with Mars, but this possibility was excluded when its orbit was determined more accurately.
All NASA Mars orbiters—including 2001 Mars Odyssey, Mars Reconnaissance Orbiter and MAVEN—as well as ESA's orbiter, Mars Express, and ISRO's satellite, the Mars Orbiter Mission, reported a healthy status after the comet flyby on 19 October 2014. During the flyby, orbiters around Mars detected thousands of kilograms per hour of comet dust composed of magnesium, iron, sodium, potassium, manganese, nickel, chromium and zinc. In addition, the comet nucleus was determined to be between 400 and 700 meters (0.2 and 0.4 mi), much smaller than originally assumed. The nucleus rotates once every eight hours.
Discovery
The comet was discovered on 3 January 2013 by professional astronomer Robert McNaught at the Siding Spring Observatory at Coonabarabran NSW Australia and received the official designation C/2013 A1. It was named Siding Spring based on a tradition to identify the observatory that discovered it. Three images were obtained through the use of a CCD camera mounted on the Uppsala Southern Schmidt Telescope with a spherical mirror of 0.5 meters in diameter. Comet Siding Spring had an apparent magnitude of 18.4 to 18.6. At the time of its discovery, it was 7.2 AU (1.08×109 km; 670,000,000 mi) from the Sun.
Precovery images by the Catalina Sky Survey from 8 December 2012 were found quickly and announced with the discovery giving Comet Siding Spring a 29-day observation arc. On 3 March 2013, Pan-STARRS precovery images from 4 October 2012 were announced that extended the observation arc to 148 days.
Encounter with Mars
Comet Siding Spring passed extremely close to Mars on 19 October 2014 at 18:28 ± 0:01 UTC. Initial observations by Leonid Elenin on 27 February 2013, suggested that it might pass 0.000276 AU (41,300 km; 25,700 mi) from the center of Mars. With an observation arc of 733 days, the nominal pass is 0.000931 AU (139,300 km; 86,500 mi) from the center-point of Mars and the uncertainty region shows that it would not come closer than 0.000927 AU (138,700 km; 86,200 mi).
For comparison, Mars's outer moon Deimos orbits it at a distance of 0.00016 AU (24,000 km; 15,000 mi). Due to the uncertainty region, there was the possibility that it could pass Mars as far away as 0.000934 AU (139,700 km; 86,800 mi). It passed Mars at a relative velocity of 56 km/s (35 mi/s). As seen from Mars, C/2013 A1 peaked at approximately apparent magnitude −6.
Predicted effects
The main body of the comet's tail is projected to miss Mars by some 10 Mars diameters. As a result, only higher-than-average-velocity meteoroid dust, ejected earlier in the approach of the comet, allow for impacts on Mars, its moons, and orbiting spacecraft. Dust particles ejected from the nucleus of the comet, at more than double the expected velocity when the comet was 3 AU from the Sun, could reach Mars approximately 43 to 130 min after the closest approach of the comet. There is a possibility for millimeter- to centimeter-size particles released more than 13 AU from the Sun, however, this is considered unlikely, although massive ejections from farther out have been deduced.
In 2013 it was thought possible that Comet Siding Spring would create a meteor shower on Mars or be a threat to the spacecraft in Mars orbit. Studies in 2014 showed the threat to orbiting spacecraft to be minimal. The greatest threat would be about 100 minutes after closest approach. Mars passed about 27,000 km (17,000 mi) from the comet's orbit around 20:10 UT.
The coma of the comet is projected to more than double the amount of hydrogen in the high atmosphere for a period of several tens of hours and to warm it by about 30 K for a few hours—the combination increasing the effect of atmospheric drag on the Mars Reconnaisance Orbiter and MAVEN spacecraft causing a measurable increase in orbital decay because of atmospheric ram pressure. These spacecraft will be approaching Mars to minimum altitudes of 250 km and 150 km and orbital periods of 3 and 4 hours, respectively. The amount of drag cannot be narrowed down greatly until the production rate of the comet is known, but it could be from 1.6 to 40 times normal drag. MAVEN, in particular, also has instruments to observe any changes to the gas composition of the atmosphere. The closest orbiting moon of Mars, Phobos, orbits far higher, at a minimum distance of 9,234.42 km (5,738.00 mi), more than 10 times the height of Mars's atmosphere.
Estimates for the diameter of the nucleus have varied from 1 to 50 km (1 to 31 mi), but now the nucleus is known to be only approximately 400–700 meters (0.2–0.4 mi) in diameter, roughly the diameter of asteroid 2010 XG11 that approached Mars on 29 July 2014. Based on early upper-limit size estimates, the resulting upper-limit energy of a hypothetical impact with Mars was 24 billion megatons. The diameter of such a hypothetical impact crater would be roughly ten times the diameter of the comet's nucleus. A 700-meter impactor would create around a 7–10 km (4–6 mi) crater.
The odds of an impact with Mars were 1 in 1250 in March 2013, 1 in 2000 in late March 2013, 1 in 8000 by April 2013, and 1 in 120,000 by 8 April 2013. The 8 April 2013 JPL Small-Body Database 3-sigma solution was the first estimate to show that the minimum approach by Comet Siding Spring would miss Mars.
Actual effects
Maven detected an intense meteor shower. Comet Siding Spring has a rotation period of approximately 8 hours. Debris from Comet Siding Spring added a temporary, but strong layer of ions to Mars's ionosphere (the first time such a phenomenon has been observed on any planet), and a few tons of cometary dust were vaporized high in Mars's atmosphere. Magnesium, iron, and other metals were observed to have had been deposited. An observer on the surface would have seen a few tens of meteors during the plane crossing.
During the flyby of Mars at a proximity of 140,000 km, Comet Siding Spring's magnetic field, generated by its interaction with the solar wind, caused a violent turmoil that lasted for several hours, long after its flyby. Its coma washed over Mars with the dense inner coma, reaching or almost reaching the planet's surface. The cometary magnetic field temporarily merged with and overwhelmed Mars's weak magnetic field.
Observation
As seen from Earth, on 19 October 2014, Mars was in the constellation Ophiuchus, near globular cluster NGC 6401, and 60 degrees from the Sun. Mars and C/2013 A1 were 1.6 AU (240,000,000 km; 150,000,000 mi) from Earth. As of October 2014, C/2013 A1 had an apparent magnitude of roughly 11 and was the third-brightest comet in the sky at that time. At an apparent magnitude of 0.9, Mars was estimated to be about 11,000 times brighter than the diffuse-looking comet with a low-surface brightness. To observe C/2013 A1 visually from Earth would have required a telescope with an optical mirror at least 0.2-meter (8 in) in diameter. By November 2014 the comet had dimmed to magnitude 11.6 and was only around the fifth-brightest comet in the sky.
Mars and Comet Siding Spring were visible to the STEREO-A spacecraft during the 2014 encounter. In orbit around Mars were the spacecraft Mars Reconnaissance Orbiter, 2001 Mars Odyssey, ESA's Mars Express, MAVEN, and the Indian Mars Orbiter Mission (Mangalyaan). The last two missions had arrived less than one month before the closest approach of C/2013 A1 to Mars. All these artificial satellites may have been exposed to potentially damaging particles. The level of exposure will not be known for months, but NASA had taken several "precautionary measures" as it prepared to study C/2013 A1. Two key strategies to lessen the risk were to place the orbiters on the opposite side of Mars at the time of the highest risk and to orient the orbiters so that their most vulnerable parts were not in the line of impact. On the ground, the Curiosity and Opportunity rovers obtained images as well. Results from the observations will be discussed during a special session "Comet C/2013 A1 Siding Spring at Mars" at the 2014 AGU Fall Meeting in San Francisco on 18 December 2014.
Image Credit: ESA/Hubble & NASA, Jean-Christophe Lambry
Explanation from: https://en.wikipedia.org/wiki/C/2013_A1
The Galactic Centre and Sagittarius B2
Colour-composite image of the Galactic Centre and Sagittarius B2 as seen by the ATLASGAL survey. The centre of the Milky Way is home to a supermassive black hole more than four million times the mass of our Sun. It is about 25 000 light years from Earth. Sagittarius B2 (Sgr B2) is one of the largest clouds of molecular gas in the Milky Way. This dense region lies close to the Galactic Centre and is rich in many different interstellar molecules.
In this image, the ATLASGAL submillimetre-wavelength data are shown in red, overlaid on a view of the region in infrared light, from the Midcourse Space Experiment (MSX) in green and blue. Sagittarius B2 is the bright orange-red region to the middle left of the image, which is centred on the Galactic Centre.
Image Credit: ESO/APEX & MSX/IPAC/NASA
Explanation from: https://www.eso.org/public/images/eso0924e/
Spiral Galaxy NGC 4565
The first galaxy pictured here is NGC 4565, which for obvious reasons is also called the Needle Galaxy. First spotted in 1785 by Uranus' discoverer, Sir William Herschel (1738-1822), this is one of the most famous example of an edge-on spiral galaxy and is located some 30 million light-years away in the constellation Coma Berenices (Berenice's Hair). It displays a bright yellowish central bulge that juts out above most impressive dust lanes.
Because it is relatively close (it is only 12 times farther away than Messier 31, the Andromeda galaxy, which is the major galaxy closest to us) and relatively large (roughly one third larger than the Milky Way), it does not fit entirely into the field of view of the FORS instrument (about 7 x 7 arcmin2).
Many background galaxies are also visible in this FORS image, giving full meaning to their nickname of "island universes".
Image Credit: ESO
Explanation from: https://www.eso.org/public/images/eso0525a/
December 19, 2016
Lenticular Clouds over Mount Rainier
The summit of Washington's Mount Rainier lies hidden beneath a stack of horizontally layered lenticular clouds. These clouds are formed by high winds blowing over rough terrain and are sometimes described as a "stack of pancakes."
Mount Rainier, Washington, USA
Image Credit: Arco Images/Alamy
Campbell’s Hydrogen star HD 184738
This image, snapped by NASA/ESA Hubble Space Telescope, shows the star HD 184738, also known as Campbell’s hydrogen star. It is surrounded by plumes of reddish gas — the fiery red and orange hues are caused by glowing gases, including hydrogen and nitrogen.
HD 184738 is at the centre of a small planetary nebula. The star itself is known as a [WC] star, a rare class resembling their much more massive counterparts — Wolf-Rayet stars. These stars are named after two French astronomers, Charles Wolf and Georges Rayet, who first identified them in the mid-nineteenth century.
Wolf-Rayet stars are hot stars, perhaps 20 times more massive than the Sun, that are rapidly blowing away material and losing mass. [WC] stars are rather different: they are low-mass Sun-like stars at the end of their lives. While these stars have recently ejected much of their original mass, the hot stellar core is still losing mass at a high rate, creating a hot wind. It is these winds that cause them to resemble Wolf-Rayet stars.
However, astronomers can look more closely at the composition of these winds to tell the stars apart; [WC] stars are identified by the carbon and oxygen in their winds. Some true Wolf-Rayet stars are rich in nitrogen instead, but this is very rare among their low-mass counterparts.
HD 184738 is also very bright in the infrared part of the spectrum, and is surrounded by dust very similar to the material that the Earth formed from. The origin of this dust is uncertain.
Image Credit: ESA/Hubble & NASA, Jean-Christophe Lambry
Explanation from: https://www.spacetelescope.org/images/potw1337a/
Freewheeling Galaxies Collide in a Blaze of Star Birth
A dusty spiral galaxy appears to be rotating on edge, like a pinwheel, as it slides through the larger, bright galaxy NGC 1275, in this NASA Hubble Space Telescope image.
These images, taken with Hubble's Wide Field Planetary Camera 2 (WFPC2), show traces of spiral structure accompanied by dramatic dust lanes and bright blue regions that mark areas of active star formation. Detailed observations of NGC 1275 indicate that the dusty material belongs to a spiral system seen nearly edge-on in the foreground. The second galaxy, lying beyond the first, is actually a giant elliptical with peculiar faint spiral structure in its nucleus. These galaxies are believed to be colliding at over 6 million miles per hour.
NGC 1275 is about 235 million light-years away in the constellation Perseus. Embedded in the center of a large cluster of galaxies known as the Perseus Cluster, it is also known to emit a powerful signal at both X-ray and radio frequencies. The galaxy collision causes the gas and dust already existing in the central bright galaxy to swirl into the center of the object. The X-ray and radio emission indicates the probable existence of a black hole at the bright galaxy's center.
While the dark dusty material in the Hubble image falls inward, NGC 1275 displays intricate filamentary structures at a much larger scale outside the image. This is a typical feature of bright cluster galaxies. Additional observational evidence of strong interactions between at least two galaxies, and possibly a few smaller galaxies, includes the formation of new stars and large star clusters. Although similar in shape to the old globular clusters in the Milky Way galaxy, NGC 1275's clusters are much younger and contain 100,000 to a million stars each.
This image was created from archived blue and red Hubble WFPC2 data taken in 1995 by John Trauger (JPL) and Jon Holtzman (NMSU). The Hubble Heritage team, along with collaborators Megan Donahue, Jennifer Mack, and Mark Voit (STScI), took follow-up WFPC2 observations at infrared wavelengths in 2001 to help produce this full-color image.
Image Credit: NGC 1275, Perseus A, 3C 84
Explanation from: http://hubblesite.org/newscenter/archive/releases/2003/14/image/a/
Planetary Nebula NGC 3699
This fetching cloud of gas was imaged by the ESO Faint Object Spectrograph and Camera (EFOSC2) at ESO's La Silla Observatory. It can be found nestled in the busy constellation of Centaurus in the skies of the southern hemisphere.
The cloud of gas — named NGC 3699 — is a planetary nebula, It is distinguished by an irregular mottled appearance and a dark rift, which roughly bisects it.
These objects, despite the name, have nothing to do with planets and are created in the final stages of the evolution of stars similar in mass to the Sun. The name "planetary nebula" arises from the time of their discovery by William Herschel, when they appeared in the telescopes of the time as rounded objects similar in looks to the planets.
Towards the end of their lives, stars like the Sun exhaust the supply of hydrogen in their cores, putting a stop to nuclear reactions. This causes the star's core to contract under the force of gravity and heat up, while the cooler outer layers expand tremendously — the surface of the Sun, for example, will likely engulf the orbit of Earth when it reaches this stage in its evolution. Unusually strong stellar winds push the gaseous outer layers of the star out into space, eventually exposing the core of the star, which begins to emit ultraviolet radiation, ionising the expelled gas, causing the nebula's ethereal glow, and producing beautiful and varied sights, such as the one in this image.
Image Credit: ESO
Explanation from: https://www.eso.org/public/images/potw1550a/
Disc of debris around an F-type star HD 181327
Using 39 of the 66 antennas of the Atacama Large Millimeter/submillimeter Array (ALMA), located 5000 metres up on the Chajnantor plateau in the Chilean Andes, astronomers have been able to detect carbon monoxide (CO) in the disc of debris around an F-type star. Although carbon monoxide is the second most common molecule in the interstellar medium, after molecular hydrogen, this is the first time that CO has been detected around a star of this type. The star, named HD 181327, is a member of the Beta Pictoris moving group, located almost 170 light-years from Earth.
Until now, the presence of CO has been detected only around a few A-type stars, substantially more massive and luminous than HD 181327. Using the superb spatial resolution and sensitivity offered by the ALMA observatory astronomers were now able to capture this stunning ring of smoke and map the density of the CO within the disc.
The study of debris discs is one way to characterise planetary systems and the results of planet formation. The CO gas is found to be co-located with the dust grains in the ring of debris and to have been produced recently. Destructive collisions of icy planetesimals in the disc are possible sources for the continuous replenishment of the CO gas. Collisions in debris discs typically require the icy bodies to be gravitationally perturbed by larger objects in order to reach sufficient collisional velocities. Moreover, the derived CO composition of the icy planetesimals in the disc is consistent with the comets in our Solar System. This possible secondary origin for the CO gas suggests that icy comets could be common around stars similar to our Sun which has strong implications for life suitability in terrestrial exoplanets.
Image Credit: ESO/Marino et al.
Explanation from: https://www.eso.org/public/images/potw1621a/
Earth's Atmosphere seen from the International Space Station
ISS, Orbit of the Earth
September 2016
Image Credit: NASA/ESA
December 18, 2016
Earth and the International Space Station seen from Space Shuttle Discovery
Backdropped by the blackness of space and the thin line of Earth's atmosphere, the International Space Station is seen from Space Shuttle Discovery as the two spacecraft begin their relative separation. Earlier the STS-119 and Expedition 18 crews concluded 9 days, 20 hours and 10 minutes of cooperative work onboard the shuttle and station. Undocking of the two spacecraft occurred at 2:53 p.m. (CDT) on March 25, 2009.
Space Shuttle Discovery, Orbit of the Earth
March 25, 2009
Image Credit: NASA
Aurora & Bárðarbunga Volcano Eruption
Vatnajökull, Iceland
September 2, 2014
Image Credit & Copyright: Gísli Dúa Hjörleifsson
Artist's impression of the hot molecular core discovered in the Large Magellanic Cloud
A hot and dense mass of complex molecules, cocooning a newborn star, has been discovered by a Japanese team of astronomers using ALMA. This unique hot molecular core is the first of its kind to have been detected outside the Milky Way galaxy. It has a very different molecular composition from similar objects in our own galaxy — a tantalising hint that the chemistry taking place across the Universe could be much more diverse than expected.
A team of Japanese researchers have used the power of the Atacama Large Millimeter/submillimeter Array (ALMA) to observe a massive star known as ST11 in our neighbouring dwarf galaxy, the Large Magellanic Cloud (LMC). Emission from a number of molecular gases was detected. These indicated that the team had discovered a concentrated region of comparatively hot and dense molecular gas around the newly ignited star ST11. This was evidence that they had found something never before seen outside of the Milky Way — a hot molecular core.
Takashi Shimonishi, an astronomer at Tohoku University, Japan, and the paper's lead author enthused: "This is the first detection of an extragalactic hot molecular core, and it demonstrates the great capability of new generation telescopes to study astrochemical phenomena beyond the Milky Way."
The ALMA observations revealed that this newly discovered core in the LMC has a very different composition to similar objects found in the Milky Way. The most prominent chemical signatures in the LMC core include familiar molecules such as sulfur dioxide, nitric oxide, and formaldehyde — alongside the ubiquitous dust. But several organic compounds, including methanol (the simplest alcohol molecule), had remarkably low abundance in the newly detected hot molecular core. In contrast, cores in the Milky Way have been observed to contain a wide assortment of complex organic molecules, including methanol and ethanol.
Takashi Shimonishi explains: “The observations suggest that the molecular compositions of materials that form stars and planets are much more diverse than we expected.”
The LMC has a low abundance of elements other than hydrogen or helium. The research team suggests that this very different galactic environment has affected the molecule-forming processes taking place surrounding the newborn star ST11. This could account for the observed differences in chemical compositions.
It is not yet clear if the large, complex molecules detected in the Milky Way exist in hot molecular cores in other galaxies. Complex organic molecules are of very special interest because some are connected to prebiotic molecules formed in space. This newly discovered object in one of our nearest galactic neighbours is an excellent target to help astronomers address this issue. It also raises another question: how could the chemical diversity of galaxies affect the development of extragalactic life?
Image Credit: FRIS/Tohoku University
Explanation from: https://www.eso.org/public/news/eso1634/
Computer simulation of a Lyman-alpha Blob
This rendering shows a snapshot from a cosmological simulation of a Lyman-alpha Blob similar to LAB-1. This simulation tracks the evolution of gas and dark matter using one of the latest models for galaxy formation running on the NASA Pleiades supercomputer. This view shows the distribution of gas within the dark matter halo, colour coded so that cold gas (mainly neutral hydrogen) appears red and hot gas appears white. Embedded at the centre of this system are two strongly star-forming galaxies, but these are surrounded by hot gas and many smaller satellite galaxies that appear as small red clumps of gas here. Lyman-alpha photons escape from the central galaxies and scatter off the cold gas associated with these satellites to give rise to an extended Lyman-alpha Blob.
Image Credit: J.Geach/D.Narayanan/R.Crain
Explanation from: https://www.eso.org/public/images/eso1632a/
Mercury
This image shows an orthographic projection of this global mosaic centered at 0°N, 0°E. The rayed crater Debussy can be seen towards the bottom of the globe and the peak-ring basin Rachmaninoff can be seen towards the eastern edge.
Image Credit: NASA/Johns Hopkins
