Hurricanes Madeline and Lester

Suomi NPP satellite, Orbit of the Earth

August 29, 2016

Image Credit: NASA Earth Observatory/Suomi NPP

Galaxy Cluster CL J1001+0220

This image contains the most distant galaxy cluster, a discovery made using data from NASA’s Chandra X-ray Observatory and several other telescopes. The galaxy cluster, known as CL J1001+0220, is located about 11.1 billion light years from Earth and may have been caught right after birth, a brief, but important stage of cluster evolution never seen before.

The remote galaxy cluster was found in data from the COSMOS survey, a project that observes the same patch of sky in many different kinds of light ranging from radio waves to X-rays. This composite shows CL J1001+0220 (CL J1001, for short) in X-rays from Chandra (purple), infrared data from ESO’s UltraVISTA telescope (red, green, and blue), and radio waves from the Atacama Large Millimeter/submillimeter Array (ALMA) (green). The diffuse X-ray emission comes from a large amount of hot gas, one of the defining elements of a galaxy cluster.

In addition to its extraordinary distance, CL J1001 is remarkable because of its high levels of star formation in galaxies near the center of the cluster.

Within about 250,000 light years of the center of the cluster (its core), eleven massive galaxies are found and nine of those display high rates of formation. Specifically, stars are forming in the cluster core at a rate equivalent to about 3,400 Suns per year.

The large amount of growth through star formation in the galaxies in CL J1001 distinguishes it from other galaxy clusters found at distances of about 10 billion light years and closer, where little growth is occurring. These results suggest that elliptical galaxies in clusters may form their stars through more violent and shorter bursts of star formation than elliptical galaxies outside clusters.

The latest study shows that CL 1001 galaxy cluster may be undergoing a transformation from a galaxy cluster that is still forming, known as a “protocluster,” to a mature one. Astronomers have never found a galaxy cluster at this precise stage. These results may also imply that star formation slows down in large galaxies within clusters after the galaxies have already come together during the development of a galaxy cluster.

Image Credit: NASA
Explanation from: http://www.nasa.gov/mission_pages/chandra/galaxy-cluster-cl-j10010220.html

Jupiter's North Pole

As NASA's Juno spacecraft closed in on Jupiter for its August 27, 2016 pass, its view grew sharper and fine details in the north polar region became increasingly visible.

The JunoCam instrument obtained this view on August 27, about two hours before closest approach, when the spacecraft was 120,000 miles (195,000 kilometers) away from the giant planet (i.e., for Jupiter's center).

Unlike the equatorial region's familiar structure of belts and zones, the poles are mottled with rotating storms of various sizes, similar to giant versions of terrestrial hurricanes. Jupiter's poles have not been seen from this perspective since the Pioneer 11 spacecraft flew by the planet in 1974.

Image Credit: NASA/JPL-Caltech/SwRI/MSSS
Explanation from: http://photojournal.jpl.nasa.gov/catalog/PIA21030

WR 25 & Tr16-244

WR 25 and Tr16-244, at the bottom of the image, are located within the open cluster Trumpler 16. This cluster is embedded within the Carina Nebula, an immense cauldron of gas and dust that lies approximately 7500 light-years from Earth in the constellation of Carina, the Keel. At the top of the image, a peculiar nebula with the shape of a "defiant" finger points towards WR25 and Tr16-244.

Image Credit: NASA, ESA and Jesús Maíz Apellániz (Instituto de Astrofísica de Andalucía, Spain)
Explanation from: http://www.spacetelescope.org/images/heic0822b/

The Helix Nebula

Six hundred and fifty light-years away in the constellation Aquarius, a dead star about the size of Earth, is refusing to fade away peacefully. In death, it is spewing out massive amounts of hot gas and intense ultraviolet radiation, creating a spectacular object called a "planetary nebula."

In this image, NASA's Hubble and Spitzer Space Telescopes have teamed up to capture the complex structure of the object, called the Helix nebula, in unprecedented detail. The composite picture is made up of visible data from Hubble and infrared data from Spitzer.

The dead star, called a white dwarf, can be seen at the center of the image as a white dot. All of the colorful gaseous material seen in the image was once part of the central star, but was lost in the death throes of the star on its way to becoming a white dwarf. The intense ultraviolet radiation being released by the white dwarf is heating and destabilizing the molecules in its surrounding environment, starting from the inside out.

Like an electric stovetop slowly heating up from the center first, the hottest and most unstable gas molecules can be seen at the center of the nebula as wisps of blue. The transition to more stable and cooler molecules is clearly depicted as the color of the gas changes from very hot (blue) to hot (yellow) and warm (red).

A striking feature of the Helix, first revealed by ground-based images, is its collection of thousands of filamentary structures, or strands of gas. In this image the filaments can be seen under the transparent blue gas as red lines radiating out from the center. Astronomers believe that the molecules in these filaments are able to stay cooler and more stable because dense clumps of materials are shielding them from ultraviolet radiation.

This image is a composite showing ionized H-alpha (green) and O III (blue) gases from the Hubble Space Telescope, and molecular hydrogen (red) from Spitzer observations at 4.5 and 8.0 microns.

Image Credit: NASA/JPL-Caltech/ESA
Explanation from: http://photojournal.jpl.nasa.gov/catalog/PIA03678

Messier 82

Composite of images of the active galaxy Messier 82 from the three Great Observatories: Hubble Space Telescope, Chandra X-Ray Observatory, and Spitzer Space Telescope. X-ray data recorded by Chandra appears here in blue, infrared light recorded by Spitzer appears in red. Hubble's observation of hydrogen emission appears in orange. Hubble's bluest observation appears in yellow-green.

Image Credit: NASA, ESA, CXC, and JPL-Caltech
Explanation from: https://www.spacetelescope.org/images/heic0604d/

Aurora and the Milky Way Galaxy

Ifjord, Finnmark, Norway

September 25, 2011

Image Credit & Copyright: Tommy Eliassen

Saturn seen by Cassini spacecraft

Saturn sits nested in its rings of ice as Cassini once again plunges toward the graceful giant.

This natural color mosaic was acquired by the Cassini spacecraft as it soared 39 degrees above the unilluminated side of the rings.

Little light makes its way through the rings to be scattered in Cassini's direction in this viewing geometry, making the rings appear somewhat dark compared to the reflective planet. The view can be contrasted with earlier mosaics designed to showcase the rings rather than the planet, which were therefore given longer exposure times.

Bright clouds play in the blue-gray skies of the north. The ring shadows continue to caress the planet as they slide farther south toward their momentary disappearance during equinox in 2009. The rings' reflected light illuminates the southern hemisphere on Saturn's night side.

The scene is reminiscent of the parting glance of NASA's Voyager 1 as it said goodbye to Saturn in 1981. Cassini, however, will continue to orbit Saturn for many years to come.

Three of Saturn's moons are visible in this image: Mimas (397 kilometers, or 247 miles across) at the 2 o'clock position, Janus (181 kilometers, or 113 miles across) at the 4 o'clock position and Pandora (84 kilometers, or 52 miles across) at the 8 o'clock position. Pandora is a faint speck just outside the narrow F ring.

This mosaic was constructed from wide-angle camera images taken just before the narrow-angle camera mosaic.

The view combines 45 images -- 15 separate sets of red, green and blue images--taken over the course of about two hours, as Cassini scanned across the entire main ring system.

The images in this view were obtained on May 9, 2007, at a distance of approximately 1.1 million kilometers (700,000 miles) from Saturn. Image scale is about 62 kilometers (39 miles) per pixel.

Image Credit: NASA/JPL/Space Science Institute
Explanation from: http://photojournal.jpl.nasa.gov/catalog/PIA08388

Star-Forming Region NGC 2467

A colourful star-forming region is featured in this stunning NASA/ESA Hubble Space Telescope image of NGC 2467. Looking like a roiling cauldron of some exotic cosmic brew, huge clouds of gas and dust are sprinkled with bright blue, hot young stars.

Strangely shaped dust clouds, resembling spilled liquids, are silhouetted against a colourful background of glowing. Like the familiar Orion Nebula, NGC 2467 is a huge cloud of gas — mostly hydrogen — that serves as an incubator for new stars.

This picture was created from images taken with the Wide Field Channel of the Advanced Camera for Surveys through three different filters (F550M, F660N and F658N, shown in blue, green and red). These filters were selected to let through different colours of red and yellow light arising from different elements in the gas. The total aggregate exposure time was about 2000 seconds and the field of view is about 3.5 arcminutes across. These data were taken in 2004.

Image Credit: NASA, ESA and Orsola De Marco (Macquarie University)
Explanation from: https://www.spacetelescope.org/images/heic1012a/

Aurora over Høgtuva Mountain

The aurora borealis over Høgtuva Mountain in Norway. The Earth's magnetic field funnels particles from the solar wind over the polar regions. More than 80 kilometres above the ground, these collide with molecules in the atmosphere causing them to glow: green and pale red for oxygen and crimson for nitrogen.

Image Credit & Copyright: Tommy Eliassen
Explanation by: Royal Observatory Greenwich

The NGC 7814 Galaxy

Galaxies can take many shapes and be oriented any way relative to us in the sky. This can make it hard to figure out their actual morphology, as a galaxy can look very different from different viewpoints. A special case is when we are lucky enough to observe a spiral galaxy directly from its edge, providing us with a spectacular view like the one seen in this picture.

This is NGC 7814, also known as the “Little Sombrero”. Its larger namesake the Sombrero Galaxy is another stunning example of an edge-on galaxy — in fact, the “Little Sombrero” is about the same size as its bright namesake at about 60 000 light-years across, but as it lies further away, it appears smaller in the sky.

NGC 7814 has a bright central bulge and a bright halo of glowing gas extending outwards into space. The dusty spiral arms appear as dark streaks. they consist of dusty material that absorbs and blocks light from the galactic centre behind it. The field of view of this NASA/ESA Hubble Space Telescope image would be very impressive even without NGC 7814 in front; nearly all the objects seen in this image are galaxies as well.

Image Credit: ESA/Hubble & NASA, Josh Barrington
Explanation from: https://www.spacetelescope.org/images/potw1505a/

Open Star Cluster NGC 290

Hubble has captured the most detailed image to date of the open star cluster NGC 290 in the Small Magellanic Cloud.

The image taken with the Advanced Camera for Surveys onboard the NASA/ESA Hubble Space Telescope show a myriad of stars in crystal clear detail. The brilliant open star cluster, NGC 290, is located about 200,000 light-years away and is roughly 65 light-years across.

Image Credit: European Space Agency & NASA

Alpha Centauri A & Alpha Centauri B

The closest star system to the Earth is the famous Alpha Centauri group. Located in the constellation of Centaurus (The Centaur), at a distance of 4.3 light-years, this system is made up of the binary formed by the stars Alpha Centauri A and Alpha Centauri B, plus the faint red dwarf Alpha Centauri C, also known as Proxima Centauri.

The NASA/ESA Hubble Space Telescope has given us this stunning view of the bright Alpha Centauri A (on the left) and Alpha Centauri B (on the right), flashing like huge cosmic headlamps in the dark. The image was captured by the Wide Field and Planetary Camera 2 (WFPC2). WFPC2 was Hubble’s most used instrument for the first 13 years of the space telescope’s life, being replaced in 2009 by WFC3 during Servicing Mission 4. This portrait of Alpha Centauri was produced by observations carried out at optical and near-infrared wavelengths.

Compared to the Sun, Alpha Centauri A is of the same stellar type G2, and slightly bigger, while Alpha Centauri B, a K1-type star, is slightly smaller. They orbit a common centre of gravity once every 80 years, with a minimum distance of about 11 times the distance between the Earth and the Sun. Because these two stars are, together with their sibling Proxima Centauri, the closest to Earth, they are among the best studied by astronomers. And they are also among the prime targets in the hunt for habitable exoplanets. Using the HARPS instrument astronomers already discovered a planet orbiting Alpha Centauri B. 24 August 2016 astronomers announced the discovery of an Earth-like planet in the habitable zone orbiting the star Proxima Centauri.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1635a/

Star-Forming Region NGC 281

This wide-field view of the star-forming region NGC 281 in the constellation Cassiopeia was taken with the WIYN 0.9-meter telescope at Kitt Peak National Observatory near Tucson, Arizona, USA

Image Credit: T.A. Rector/University of Alaska Anchorage and WIYN/AURA/NSF

Supernova Remnant IC 443

This oddly colorful nebula is the supernova remnant IC 443 as seen by NASA's Wide-field Infrared Survey Explorer, or WISE. Also known as the Jellyfish nebula, IC 443 is particularly interesting because it provides a look into how stellar explosions interact with their environment. IC 443 can be found near the star Eta Geminorum, which lies near Castor, one of the twins in the constellation Gemini.

Just like human beings, stars have a life cycle -- they are born, mature and eventually die. The manner in which stars die depends on their mass. Stars with mass similar to the sun typically become planetary nebulae at the end of their lives, whereas stars with many times the sun's mass explode as supernovae. IC 443 is the remains of a star that went supernova somewhere between 5,000 and 10,000 years ago. The blast from the supernova sent out shock waves that traveled through space, sweeping up and heating the surrounding gas and dust in the interstellar medium, and creating the supernova remnant seen in this image.

What is unusual about the IC 443 is that its shell-like form has two halves that have different radii, structures and emissions. The larger northeastern shell, seen here as the violet-colored semi-circle on the top left of the supernova remnant, is composed of sheet-like filaments that are emitting light from iron, neon, silicon and oxygen gas atoms, in addition to dust particles, all heated by the blast from the supernova. The smaller southern shell, seen here in a bright cyan color on the bottom half of the image, is constructed of denser clumps and knots primarily emitting light from hydrogen gas and heated dust. These clumps are part of a molecular cloud, which can be seen in this image as the greenish cloud cutting across IC 443 from the northwest to southeast. The color differences seen in this image represent different wavelengths of infrared emission.

The differences in color are also the result of differences in the energies of the shock waves hitting the interstellar medium. The northeastern shell was probably created by a fast shock wave (100 kilometers per second or 223,700 miles per hour), whereas the southern shell was probably created by a slow shock wave (30 kilometers per second or 67,100 miles per hour).

All WISE featured images use color to represent specific infrared wavelengths. Blue represents 3.4-micron light, cyan represents 4.6-micron light, green represents 12-micron light and red represents 22-micron light. In this image, we see a mixing of blue and cyan in the southern ridge that is not often seen in other WISE images. The northeastern shell appears violet, indicating a mixture of longer infrared wavelengths from cooler dust (red) and shorter infrared wavelengths from luminescent gas (blue).

Image Credit: NASA/JPL-Caltech/UCLA
Explanation from: http://photojournal.jpl.nasa.gov/catalog/PIA13449

Omega Centauri

Omega Centauri has been known as an unusual globular cluster for a long time. A new result obtained by the NASA/ESA Hubble Space Telescope and the Gemini Observatory reveals that the explanation behind Omega Centauri's peculiarities may be a black hole hidden in its centre. One implication of the discovery is that it is very likely that Omega Centauri is not a globular cluster at all, but a dwarf galaxy stripped of its outer stars, as some scientists have suspected for a few years.

A new discovery has resolved some of the mystery surrounding Omega Centauri, the largest and brightest globular cluster in the sky. Images obtained with the Advanced Camera for Surveys onboard the NASA/ESA Hubble Space Telescope and data obtained by the GMOS spectrograph on the Gemini South telescope in Chile show that Omega Centauri appears to harbour an elusive intermediate-mass black hole in its centre. "This result shows that there is a continuous range of masses for black holes, from supermassive, to intermediate-mass, to small stellar mass types", explained astronomer Eva Noyola of the Max-Planck Institute for Extraterrestrial Physics in Garching, Germany, and leader of the team that made the discovery.

Omega Centauri is visible from Earth with the naked eye and is one of the favourite celestial objects for stargazers from the southern hemisphere. Although the cluster is 17 000 light-years away, located just above the plane of the Milky Way, it appears almost as large as the full Moon when the cluster is seen from a dark rural area. Exactly how Omega Centauri should be classified has always been a contentious topic. It was first listed in Ptolemy's catalogue nearly two thousand years ago as a single star. Edmond Halley reported it as a nebula in 1677. In the 1830s the English astronomer John Herschel was the first to recognise it as a globular cluster. Now, more than a century later, this new result suggests Omega Centauri is not a globular cluster at all, but a dwarf galaxy stripped of its outer stars.

Globular clusters consist of up to one million old stars tightly bound by gravity and are found in the outskirts of many galaxies including our own. Omega Centauri has several characteristics that distinguish it from other globular clusters: it rotates faster than a run-of-the-mill globular cluster, its shape is highly flattened and it consists of several generations of stars -- more typical globulars usually consist of just one generation of old stars.

Moreover, Omega Centauri is about 10 times as massive as other big globular clusters, almost as massive as a small galaxy. These peculiarities have led astronomers to suggest that Omega Centauri may not be a globular cluster at all, but a dwarf galaxy stripped of its outer stars by an earlier encounter with the Milky Way. "Finding a black hole at the heart of Omega Centauri could have profound implications for our understanding of its past interaction with the Milky Way", said Noyola.

Eva Noyola and her colleagues measured the motions and brightnesses of the stars at the centre of Omega Centauri. The measured velocities of the stars in the centre are related to the total mass of the cluster and were far higher than expected from the mass deduced from the number and type of stars seen. So, there had to be something extraordinarily massive (and invisible) at the centre of the cluster responsible for the fast-swirling dance of stars -- almost certainly a black hole with a mass of 40 000 solar masses. "Before this observation, we had only one example of an intermediate-mass black hole -- in the globular cluster G1, in the nearby Andromeda Galaxy", said astronomer Karl Gebhardt of the University of Texas at Austin, USA, and a member of the team that made the discovery.

Although the presence of an intermediate-mass black hole is the most likely reason for the stellar speedway near the cluster's centre, astronomers have analysed a couple of other possible causes: a collection of unseen burnt-out stars such as white dwarfs or neutron stars adding extra mass, or a group of stars with elongated orbits that would make the stars closest to the centre appear to speed up.

According to Noyola these alternative scenarios are unlikely: "The normal evolution of a star cluster like Omega Centauri should not end up with stars behaving in those ways. Even if we assume that either scenario did happen somehow, both configurations are expected to be very short-lived. A clump of burnt-out stars, for example, is expected to move farther away from the cluster centre quickly. For stars with elongated orbits, these orbits are expected to become circular very quickly."

According to scientists, these intermediate-mass black holes could turn out to be "baby" supermassive black holes. "We may be on the verge of uncovering one possible mechanism for the formation of supermassive black holes. Intermediate-mass black holes like this could be the seeds of full-sized supermassive black holes." Astronomers have debated the existence of intermediate-mass black holes because they have not found strong evidence for them and there is no widely accepted mechanism for how they could form. They have ample evidence that small black holes of a few solar masses are produced when giant stars die. There is similar evidence that supermassive black holes weighing the equivalent of millions to billions of solar masses sit at the heart of many galaxies, including our own Milky Way.

Intermediate-mass black holes may be rare and exist only in former dwarf galaxies that have been stripped of their outer stars, but they could also be more common than expected, existing at the centres of globular clusters as well. A previous Hubble survey of supermassive black holes and their host galaxies showed a correlation between the mass of a black hole and that of its host. Astronomers estimate that the mass of the dwarf galaxy that may have been the precursor of Omega Centauri was roughly 10 million solar masses. If lower mass galaxies obey the same rule as more massive galaxies that host supermassive black holes, then the mass of Omega Centauri does match that of its black hole.

The team will use the European Southern Observatory's Very Large Telescope in Paranal, Chile to conduct follow-up observations of the velocity of the stars near the cluster's centre to confirm the discovery.

Image Credit: NASA, ESA and the Hubble Heritage Team (STScI/AURA), A. Cool (San Francisco State Univ.) and J. Anderson (STScI)
Explanation from: https://www.spacetelescope.org/news/heic0809/

Messier 87: Giant Galaxy is Still Growing

Observations with ESO’s Very Large Telescope have revealed that the giant elliptical galaxy Messier 87 has swallowed an entire medium-sized galaxy over the last billion years. For the first time a team of astronomers has been able to track the motions of 300 glowing planetary nebulae to find clear evidence of this event and also found evidence of excess light coming from the remains of the totally disrupted victim.

Astronomers expect that galaxies grow by swallowing smaller galaxies. But the evidence is usually not easy to see — just as the remains of the water thrown from a glass into a pond will quickly merge with the pond water, the stars in the infalling galaxy merge in with the very similar stars of the bigger galaxy leaving no trace.

But now a team of astronomers led by PhD student Alessia Longobardi at the Max-Planck-Institut für extraterrestrische Physik, Garching, Germany has applied a clever observational trick to clearly show that the nearby giant elliptical galaxy Messier 87 merged with a smaller spiral galaxy in the last billion years.

"This result shows directly that large, luminous structures in the Universe are still growing in a substantial way — galaxies are not finished yet!" says Alessia Longobardi. "A large sector of Messier 87's outer halo now appears twice as bright as it would if the collision had not taken place."

Messier 87 lies at the centre of the Virgo Cluster of galaxies. It is a vast ball of stars with a total mass more than a million million times that of the Sun, lying about 50 million light-years away.

Rather than try to look at all the stars in Messier 87 — there are literally billions and they are too faint and numerous be studied individually — the team looked at planetary nebulae, the glowing shells around ageing stars. Because these objects shine very brightly in a specific hue of aquamarine green, they can be distinguished from the surrounding stars. Careful observation of the light from the nebulae using a powerful spectrograph can also reveal their motions.

Just as the water from a glass is not visible once thrown into the pond — but may have caused ripples and other disturbances that can be seen if there are particles of mud in the water — the motions of the planetary nebulae, measured using the FLAMES spectrograph on the Very Large Telescope, provide clues to the past merger.

"We are witnessing a single recent accretion event where a medium-sized galaxy fell through the centre of Messier 87, and as a consequence of the enormous gravitational tidal forces, its stars are now scattered over a region that is 100 times larger than the original galaxy!" adds Ortwin Gerhard, head of the dynamics group at the Max-Planck-Institut für extraterrestrische Physik, Garching, Germany, and a co-author of the new study.

The team also looked very carefully at the light distribution in the outer parts of Messier 87 and found evidence of extra light coming from the stars in the galaxy that had been pulled in and disrupted. These observations have also shown that the disrupted galaxy has added younger, bluer stars to Messier 87, and so it was probably a star-forming spiral galaxy before its merger.

"It is very exciting to be able to identify stars that have been scattered around hundreds of thousands of light-years in the halo of this galaxy — but still to be able to see from their velocities that they belong to a common structure. The green planetary nebulae are the needles in a haystack of golden stars. But these rare needles hold the clues to what happened to the stars," concludes co-author Magda Arnaboldi (ESO, Garching, Germany).

Image Credit: Chris Mihos (Case Western Reserve University)/ESO
Explanation from: http://www.eso.org/public/news/eso1525/

Venus

Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. It has the longest rotation period (243 days) of any planet in the Solar System and rotates in the opposite direction to most other planets. It has no natural satellite. It is named after the Roman goddess of love and beauty. It is the second-brightest natural object in the night sky after the Moon, reaching an apparent magnitude of −4.6, bright enough to cast shadows. Because Venus is an inferior planet from Earth, it never appears to venture far from the Sun; its elongation reaches a maximum of 47.8°.

Venus is a terrestrial planet and is sometimes called Earth's "sister planet" because of their similar size, mass, proximity to the Sun, and bulk composition. It is radically different from Earth in other respects. It has the densest atmosphere of the four terrestrial planets, consisting of more than 96% carbon dioxide. The atmospheric pressure at the planet's surface is 92 times that of Earth. Venus is by far the hottest planet in the Solar System, with a mean surface temperature of 735 K (462 °C; 863 °F), even though Mercury is closer to the Sun. Venus is shrouded by an opaque layer of highly reflective clouds of sulfuric acid, preventing its surface from being seen from space in visible light. It may have had water oceans in the past, but these would have vaporized as the temperature rose due to a runaway greenhouse effect. The water has probably photodissociated, and the free hydrogen has been swept into interplanetary space by the solar wind because of the lack of a planetary magnetic field. Venus's surface is a dry desertscape interspersed with slab-like rocks and is periodically resurfaced by volcanism.

As one of the brightest objects in the sky, Venus has been a major fixture in human culture for as long as records have existed. It has been made sacred to gods of many cultures, and has been a prime inspiration for writers and poets as the "morning star" and "evening star". Venus was the first planet to have its motions plotted across the sky, as early as the second millennium BC, and was a prime target for early interplanetary exploration as the closest planet to Earth. It was the first planet beyond Earth visited by a spacecraft (Mariner 2) in 1962, and the first to be successfully landed on (by Venera 7) in 1970. Venus's thick clouds render observation of its surface impossible in visible light, and the first detailed maps did not emerge until the arrival of the Magellan orbiter in 1991. Plans have been proposed for rovers or more complex missions, but they are hindered by Venus's hostile surface conditions.

Image Credit: NASA/JPL
Explanation from: https://en.wikipedia.org/wiki/Venus

U Camelopardalis

A bright star is surrounded by a tenuous shell of gas in this unusual image from the NASA/ESA Hubble Space Telescope. U Camelopardalis, or U Cam for short, is a star nearing the end of its life. As it begins to run low on fuel, it is becoming unstable. Every few thousand years, it coughs out a nearly spherical shell of gas as a layer of helium around its core begins to fuse. The gas ejected in the star’s latest eruption is clearly visible in this picture as a faint bubble of gas surrounding the star.

U Cam is an example of a carbon star. This is a rare type of star whose atmosphere contains more carbon than oxygen. Due to its low surface gravity, typically as much as half of the total mass of a carbon star may be lost by way of powerful stellar winds.

Located in the constellation of Camelopardalis (The Giraffe), near the North Celestial Pole, U Cam itself is actually much smaller than it appears in Hubble’s picture. In fact, the star would easily fit within a single pixel at the centre of the image. Its brightness, however, is enough to overwhelm the capability of Hubble’s Advanced Camera for Surveys making the star look much bigger than it really is.

The shell of gas, which is both much larger and much fainter than its parent star, is visible in intricate detail in Hubble’s portrait. While phenomena that occur at the ends of stars’ lives are often quite irregular and unstable, the shell of gas expelled from U Cam is almost perfectly spherical.

The image was produced with the High Resolution Channel of the Advanced Camera for Surveys.

Image Credit: ESA/Hubble, NASA and H. Olofsson (Onsala Space Observatory)
Explanation from: https://www.spacetelescope.org/images/potw1227a/

Jupiter seen by Cassini spacecraft

This true color mosaic of Jupiter was constructed from images taken by the narrow angle camera onboard NASA's Cassini spacecraft on December 29, 2000, during its closest approach to the giant planet at a distance of approximately 10 million kilometers (6.2 million miles).

It is the most detailed global color portrait of Jupiter ever produced; the smallest visible features are approximately 60 kilometers (37 miles) across. The mosaic is composed of 27 images: nine images were required to cover the entire planet in a tic-tac-toe pattern, and each of those locations was imaged in red, green, and blue to provide true color. Although Cassini's camera can see more colors than humans can, Jupiter's colors in this new view look very close to the way the human eye would see them.

Everything visible on the planet is a cloud. The parallel reddish-brown and white bands, the white ovals, and the large Great Red Spot persist over many years despite the intense turbulence visible in the atmosphere. The most energetic features are the small, bright clouds to the left of the Great Red Spot and in similar locations in the northern half of the planet. These clouds grow and disappear over a few days and generate lightning. Streaks form as clouds are sheared apart by Jupiter's intense jet streams that run parallel to the colored bands. The prominent dark band in the northern half of the planet is the location of Jupiter's fastest jet stream, with eastward winds of 480 kilometers (300 miles) per hour. Jupiter's diameter is eleven times that of Earth, so the smallest storms on this mosaic are comparable in size to the largest hurricanes on Earth.

Unlike Earth, where only water condenses to form clouds, Jupiter's clouds are made of ammonia, hydrogen sulfide, and water. The updrafts and downdrafts bring different mixtures of these substances up from below, leading to clouds at different heights. The brown and orange colors may be due to trace chemicals dredged up from deeper levels of the atmosphere, or they may be byproducts of chemical reactions driven by ultraviolet light from the Sun. Bluish areas, such as the small features just north and south of the equator, are areas of reduced cloud cover, where one can see deeper.

Image Credit: NASA/JPL/Space Science Institute

Explanation from: http://photojournal.jpl.nasa.gov/catalog/PIA04866

Globular Cluster NGC 6397

Image of globular cluster NGC 6397 in the constellation Ara (the Altar). The cluster is home to a highly unusual system consisting of a fast spinning pulsar and a bloated red companion star.

Image Credit: NASA, ESA and H. Richer (University of British Columbia)