This photograph of the southern hemisphere of Jupiter was obtained by Voyager 2 on June 25, 1979, at a distance of 12 million kilometers (8 million miles). Seen in front of the turbulent clouds of the planet is Io, the innermost of the large Galilean satellites of Jupiter. Io is the size of our moon. Voyager discovered that Io is the most volcanically active planetary body known in the solar system, with continuous eruptions much larger than any that take place on the Earth. The red, orange, and yellow colors of Io are thought to be deposits of sulfur and sulfur compounds produced in these eruptions. The smallest features in either Jupiter or Io that can be distinguished in this picture are about 200 kilometers (125 miles) across.
A solar eruption gracefully rose up from the Sun on December 31, 2012, twisting and turning. Magnetic forces drove the flow of plasma, but without sufficient force to overcome the Sun's gravity much of the plasma fell back into the Sun.
The length of the eruption extends about 160,000 miles out from the Sun. With Earth about 7,900 miles in diameter, this relatively minor eruption is about 20 times the diameter of our planet.
This image from the NASA/ESA Hubble Space Telescope shows NGC 7026, a planetary nebula. Located just beyond the tip of the tail of the constellation of Cygnus (The Swan), this butterfly-shaped cloud of glowing gas and dust is the wreckage of a star similar to the Sun.
Planetary nebulae, despite their name, have nothing to do with planets. They are in fact a relatively short-lived phenomenon that occurs at the end of the life of mid-sized stars. As a star’s source of nuclear fuel runs out, its outer layers are puffed out, leaving only the hot core of the star behind. As the gaseous envelope heats up, the atoms in it are excited, and it lights up like a fluorescent sign.
Fluorescent lights on Earth get their bright colours from the gases they are filled with. Neon signs, famously, produce a bright red colour, while ultraviolet lights (black lights) typically contain mercury. The same goes for nebulae: their vivid colours are produced by the mix of gases present in them.
This image of NGC 7026 shows starlight in green, light from glowing nitrogen gas in red, and light from oxygen in blue (in reality, this appears green, but the colour in this image has been shifted to increase the contrast).
As well as visible light, NGC 7026 emits X-ray radiation, and has been studied by ESA’s XMM-Newton space telescope. X-rays are a result of the extremely high temperatures of the gas in NGC 7026.
This image was produced by the Wide Field and Planetary Camera 2 aboard the Hubble Space Telescope. The image is 35 by 35 arcseconds.
Image Credit: ESA/Hubble & NASA, Linda Morgan-O'Connor
Explanation from: https://www.spacetelescope.org/images/potw1222a/
Galaxies come in a variety of shapes and sizes, and these features change as they evolve. Some, like the galaxy in the centre of this NASA/ESA Hubble Space Telescope image, are beautiful spirals with graceful curved arms, while others are fuzzy oval-shaped blobs like the large object showing up near the bottom right of the frame. Others still are rather irregular in shape, such as the orange galaxy at the top of the image, which resembles a tiny wobbling string.
This picture is one of the few hundred exposures taken with Hubble’s Advanced Camera for Surveys to assemble the “Extended Groth Strip”. This strip, named after the Princeton University astronomer Edward Groth, is a composite picture of a rectangular region of the sky in the constellation of Ursa Major. It covers a relatively small area in the sky — equivalent to roughly the width of a finger stretched at arms’ length — but includes at least 50 000 galaxies.
The images that make up the Extended Groth Strip allow astronomers to peer into the last eight billion years of the Universe’s history and to see galaxies at various stages of their evolution. The large elliptical and spiral objects we see in the foreground of this image are fully-formed adult galaxies. But many of the ones in the background, fuzzier and more peculiar in shape, are representative of a time when galaxies were undergoing active formation.
Images like these help astronomers to understand how galaxies change in size and shape as they evolve, from their early formative years — punctuated by violent events such as the growth of the vast black holes at their centres and collisions with other galaxies — into their quieter adult lives.
This picture was created from visible and infrared exposures taken with the Wide Field Channel of Hubble’s Advanced Camera for Surveys.
Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1141a/
More dust blows out of the Sahara Desert and into the atmosphere than from any other desert in the world, and more than half of the dust deposited in the ocean lifts off from these arid North African lands. Saharan dust influences the fertility of Atlantic waters and soils in the Americas. It blocks or reflects sunlight and affects the formation of clouds. By way of the dry Saharan air layer, dust either promotes or suppresses the development of Atlantic hurricanes, an enigma that scientists are trying to sort out.
In early September 2014, it looked like this sandy landscape had changed places with the sky. The photograph above was taken by astronaut Alex Gerst on September 8, 2014, from the International Space Station. The ISS was over Libya at the time, and Gerst was looking south-southwest over a storm that stretched hundreds of kilometers across the sand seas of the Sahara.
In the photo, winds appear to be coming out of the east or northeast (left), and the sun is setting to the west (right in this image). Billowing cumulus and cumulonimbus clouds suggest that a cold, windy front was moving across the desert, perhaps a haboob. The African land surface was almost completely blocked from view by the thick dust; even the lower portions of some clouds were obscured.
“It's a spectacular image,” said Leo Donner, an atmospheric physicist at NOAA’s Geophysical Fluid Dynamics Laboratory. “What appear to be convective anvils are protruding above a dusty layer, and I’d speculate that the narrower convection cells on which these anvils are resting are obscured by the thick dust. The four small cylinders with tops that look like chess figures [upper right] have structures very much like the idealized plumes we use for cumulus convection in climate models.”
Atmospheric scientist Matt McGill of NASA’s Goddard Space Flight Center is flying one instrument on a robotic plane to study such dust plumes and clouds, and he has another one headed for the ISS later this year. The Cloud-Physics Lidar (CPL) is mounted on NASA’s Global Hawk unmanned drone and has been flying over tropical storms in the Atlantic. CPL is a prototype of the Cloud-Aerosol Transport System (CATS), an instrument package that is soon to be launched to the space station. The goal of both instruments is to better parse not just how much dust and other aerosols are carried in the air, but how abundant they are at various altitudes.
Image Credit: NASA
Explanation from: http://earthobservatory.nasa.gov/IOTD/view.php?id=84400
The NASA/ESA Hubble Space Telescope has captured a beautiful galaxy that, with its reddish and yellow central area, looks rather like an explosion from a Hollywood movie. The galaxy, called NGC 5010, is in a period of transition. The aging galaxy is moving on from life as a spiral galaxy, like our Milky Way, to an older, less defined type called an elliptical galaxy. In this in-between phase, astronomers refer to NGC 5010 as a lenticular galaxy, which has features of both spirals and ellipticals.
NGC 5010 is located around 140 million light-years away in the constellation of Virgo (The Virgin). The galaxy is oriented sideways to us, allowing Hubble to peer into it and show the dark, dusty, remnant bands of spiral arms. NGC 5010 has notably started to develop a big bulge in its disc as it takes on a more rounded shape.
Most of the stars in NGC 5010 are red and elderly. The galaxy no longer contains all that many of the fast-lived blue stars common in younger galaxies that still actively produce new populations of stars.
Much of the dusty and gaseous fuel needed to create fresh stars has already been used up in NGC 5010. Overt time, the galaxy will grow progressively more "red and dead”, as astronomers describe elliptical galaxies.
Hubble's Advanced Camera for Surveys (ACS) snapped this image in violet and infrared light.
Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1245a/
The NASA/ESA Hubble Space Telescope offers an impressive view of the centre of globular cluster NGC 6362. The image of this spherical collection of stars takes a deeper look at the core of the globular cluster, which contains a high concentration of stars with different colours.
Tightly bound by gravity, globular clusters are composed of old stars, which, at around 10 billion years old, are much older than the Sun. These clusters are fairly common, with more than 150 currently known in our galaxy, the Milky Way, and more which have been spotted in other galaxies.
Globular clusters are among the oldest structures in the Universe that are accessible to direct observational investigation, making them living fossils from the early years of the cosmos.
Astronomers infer important properties of globular clusters by looking at the light from their constituent stars. For many years, they were regarded as ideal laboratories for testing the standard stellar evolution theory. Among other things, this theory suggests that most of the stars within a globular cluster should be of a similar age.
Recently, however, high precision measurements performed in numerous globular clusters, primarily with the Hubble Space Telescope, has led some to question this widely accepted theory. In particular, certain stars appear younger and bluer than their companions, and they have been dubbed blue stragglers. NGC 6362 contains many of these stars.
Since they are usually found in the core regions of clusters, where the concentration of stars is large, the most likely explanation for this unexpected population of objects seems to be that they could be either the result of stellar collisions or transfer of material between stars in binary systems. This influx of new material would heat up the star and make it appear younger than its neighbours.
NGC 6362 is located about 25 000 light-years from Earth in the constellation of Ara (The Altar). British astronomer James Dunlop first observed this globular cluster on 30 June 1826.
This image was created combining ultraviolet, visual and infrared images taken with the Wide Field Channel of the Advanced Camera for Surveys and the Wide Field Camera 3.
Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1244a/
In the centre of a rich cluster of galaxies located in the direction of the constellation of Coma Berenices, lies a galaxy surrounded by a swarm of star clusters. NGC 4874 is a giant elliptical galaxy, about ten times larger than the Milky Way, at the centre of the Coma Galaxy Cluster. With its strong gravitational pull, it is able to hold onto more than 30 000 globular clusters of stars, more than any other galaxy that we know of, and even has a few dwarf galaxies in its grasp.
In this NASA/ESA Hubble Space Telescope image, NGC 4874 is the brightest object, located to the right of the frame and seen as a bright star-like core surrounded by a hazy halo. A few of the other galaxies of the cluster are also visible, looking like flying saucers dancing around NGC 4874. But the really remarkable feature of this image is the point-like objects around NGC 4874, revealed on a closer look: almost all of them are clusters of stars that belong to the galaxy. Each of these globular star clusters contains many hundreds of thousands of stars.
Recently, astronomers discovered that a few of these point-like objects are not star clusters but ultra-compact dwarf galaxies, also under the gravitational influence of NGC 4874. Being only about 200 light-years across and mostly made up of old stars, these galaxies resemble brighter and larger versions of globular clusters. They are thought to be the cores of small elliptical galaxies that, due to the violent interactions with other galaxies in the cluster, lost their gas and surrounding stars.
This Hubble image also shows many more distant galaxies that do not belong to the cluster, seen as small smudges in the background. While the galaxies in the Coma Cluster are located about 350 million light-years away, these other objects are much further out. Their light took several hundred million to billions of years to reach us.
Most unusually, the image also shows a very faint blue satellite trail, extending across the whole image, from the upper left corner of the frame to the lower right. Because Hubble’s cameras can only see a tiny part of the sky at one time, such trails are very rare.
This picture was created from optical and near-infrared exposures taken with the Wide Field Channel of Hubble’s Advanced Camera for Surveys. The field of view is 3.3 arcminutes across.
Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1138a/
The pearly wisps surrounding the central star IRAS 10082-5647 in this Hubble image certainly draw the eye towards the heavens. The divine-looking cloud is a reflection nebula, made up of gas and dust glowing softly by the reflected light of nearby stars, in this case a young Herbig Ae/Be star.
The star, like others of this type, is still a relative youngster, only a few million years old. It has not yet reached the so-called main sequence phase, where it will spend around 80% of its life creating energy by burning hydrogen in its core. Until then the star heats itself by gravitational collapse, as the material in the star falls in on itself, becoming ever denser and creating immense pressure which in turn gives off copious amounts of heat.
Stars only spend around 1% of their lives in this pre-main sequence phase. Eventually, gravitational collapse will heat the star’s core enough for hydrogen fusion to begin, propelling the star into the main sequence phase, and adulthood.
The Advanced Camera for Surveys aboard the Hubble Space Telescope captured the whorls and arcs of this nebula, lit up with the light from IRAS 10082-5647. Visible (555 nm) and near-infrared (814 nm) filters were used, coloured blue and red respectively. The field of view is around 1.3 by 1.3 arcminutes.
Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1144a/
A pair of jets protrude outwards in near-perfect symmetry in this image of Herbig-Haro object (HH) 212, taken by ESO’s already decommissioned Infrared Spectrometer And Array Camera (ISAAC).
The object lies in the constellation of Orion (The Hunter) in a dense molecular star-forming region, not far from the famous Horsehead Nebula. In regions like this, clouds of dust and gas collapse under the force of gravity, spinning faster and faster and becoming hotter and hotter until a young star ignites at the cloud’s centre. Any leftover material swirling around the newborn protostar comes together to form an accretion disc that will, under the right circumstances, eventually evolve to form the base material for the creation of planets, asteroids and comets.
Although this process is still not fully understood, it is common that a protostar and its accretion disc, as seen here edge-on, are the cause of the jets in this image. The star at the centre of HH 212 is indeed a very young star, at only a few thousand years old. Its jets are remarkably symmetric, with several knots appearing at relatively stable intervals. This stability suggests that the jet pulses vary quite regularly, and over a short timescale — maybe even as short as 30 years! Further out from the centre, large bow shocks spread out into interstellar space, caused by ejected gas colliding with dust and gas at speeds of several hundred kilometres per second.
Many different classifications are used to identify galaxies by shape and structure — NGC 7640 is a barred spiral type. These are recognisable by their spiral arms, which fan out not from a circular core, but from an elongated bar cutting through the galaxy’s centre. Our home galaxy, the Milky Way, is also a barred spiral galaxy. NGC 7640 might not look much like a spiral in this image, but this is due to the orientation of the galaxy with respect to Earth — or to Hubble, which acted as photographer in this case! We often do not see galaxies face on, which can make features such as spiral arms less obvious.
There is evidence that NGC 7640 has experienced some kind of interaction in its past. Galaxies contain vast amounts of mass, and therefore affect one another via gravity. Sometimes these interactions can be mild, and sometimes hugely dramatic, with two or more colliding and merging into a new, bigger galaxy. Understanding the history of a galaxy, and what interactions it has experienced, helps astronomers to improve their understanding of how galaxies — and the stars within them — form.
Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1706a/
The Universe is rarely static, although the timescales involved can be very long. Since modern astronomical observations began we have been observing the birthplaces of new stars and planets, searching for and studying the subtle changes that help us to figure out what is happening within.
The bright spot located at the edge of the bluish fan-shaped structure in this Hubble image is a young star called V* PV Cephei, or PV Cep. It is a favourite target for amateur astronomers because the fan-shaped nebulosity, known as GM 1-29 or Gyulbudaghian’s Nebula, changes over a timescale of months. The brightness of the star has also varied over time.
Images of PV Cep taken in 1952 showed a nebulous streak, similar to a comet’s tail. However, these had vanished when new images of the star were obtained some twenty-five years later. Instead, the blue fan-shaped nebula had appeared. Twenty-five years is a very short period on cosmic timescales, so astronomers think that the mysterious streak may have been a temporary phenomenon, such as the remnants of a massive stellar flare — similar to the solar flares we are used to seeing in the Solar System.
At the same time as this was happening, the star itself was brightening. This provided the light to illuminate the newly formed fan-shaped nebula. This brightening might be related to the start of the hydrogen-burning phase of the star, which would mean that it was reaching maturity.
PV Cep is thought to be surrounded by a disc of gas and dust, which would stop light from escaping in all directions. The fan-like appearance is therefore probably a result of starlight escaping from the dust disc and projecting onto the nebula.
PV Cep is located in the northern constellation of Cepheus at a distance of over 1600 light-years from Earth.
A busy patch of space has been captured in this image from the NASA/ESA Hubble Space Telescope. Scattered with many nearby stars, the field also has numerous galaxies in the background.
Located on the border of Triangulum Australe (The Southern Triangle) and Norma (The Carpenter’s Square), this field covers part of the Norma Cluster (Abell 3627) as well as a dense area of our own galaxy, the Milky Way.
The Norma Cluster is the closest massive galaxy cluster to the Milky Way, and lies about 220 million light-years away. The enormous mass concentrated here, and the consequent gravitational attraction, mean that this region of space is known to astronomers as the Great Attractor, and it dominates our region of the Universe.
The largest galaxy visible in this image is ESO 137-002, a spiral galaxy seen edge on. In this image from Hubble, we see large regions of dust across the galaxy’s bulge. What we do not see here is the tail of glowing X-rays that has been observed extending out of the galaxy — but which is invisible to an optical telescope like Hubble.
Observing the Great Attractor is difficult at optical wavelengths. The plane of the Milky Way — responsible for the numerous bright stars in this image — both outshines (with stars) and obscures (with dust) many of the objects behind it. There are some tricks for seeing through this — infrared or radio observations, for instance — but the region behind the centre of the Milky Way, where the dust is thickest, remains an almost complete mystery to astronomers.
This image consists of exposures in blue and infrared light taken by Hubble’s Advanced Camera for Surveys.
Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1302a/
Backdropped by a blue and white part of Earth, the International Space Station is seen from Space Shuttle Discovery as the two spacecraft begin their relative separation. Earlier the STS-128 and Expedition 20 crew concluded nine days of cooperative work onboard the shuttle and station. Undocking of the two spacecraft occurred at 2:26 p.m. (CDT) on September 8, 2009.
This NASA/ESA Hubble Space Telescope image shows a compact and distant globular star cluster that lies in one of the smallest constellations in the night sky, Delphinus (The Dolphin). Due to its modest size, great distance and relatively low brightness, NGC 7006 is often ignored by amateur astronomers. But even remote globular clusters such as this one appear bright and clear when imaged by Hubble’s Advanced Camera for Surveys.
NGC 7006 resides in the outskirts of the Milky Way. It is about 135 000 light-years away, five times the distance between the Sun and the centre of the galaxy, and it is part of the galactic halo. This roughly spherical region of the Milky Way is made up of dark matter, gas and sparsely distributed stellar clusters.
Like other remote globular clusters, NGC 7006 provides important clues that help astronomers to understand how stars formed and assembled in the halo. The cluster now pictured by Hubble has a very eccentric orbit indicating that it may have formed independently, in a small galaxy outside our own that was then captured by the Milky Way.
Although NGC 7006 is very distant for a Milky Way globular cluster, it is much closer than the many faint galaxies that can be seen in the background of this image. Each of these faint smudges is probably accompanied by many globular clusters similar to NGC 7006 that are too faint to be seen even by Hubble.
This image was taken using the Wide Field Channel of the Advanced Camera for Surveys, in a combination of visible and near-infrared light. The field of view is a little over 3 by 3 arcminutes.
Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1137a/
The tangled arms of the Pinwheel galaxy, otherwise known as Messier 101, are decked out in red in this new infrared image from NASA's Spitzer Space Telescope.
The Pinwheel galaxy is located 27 million light-years away in the constellation Ursa Major. It is what's called a flocculent spiral, which means that its spiral arms are not well defined.
In this infrared composite, the red color shows the dust, while the blue glow around the galaxy is from starlight. Blue indicates light with a wavelength of 3.6 microns, green corresponds to 4.5 microns, and red to 5.8 and 8.0 microns. The contribution from starlight (measured at 3.6 microns) has been subtracted from the 5.8- and 8-micron images to enhance the visibility of the dust features.
The shadows of Saturn's rings cast onto the planet appear as a thin band at the equator in this image taken as the planet approached its August 2009 equinox.
The novel illumination geometry that accompanies equinox lowers the sun's angle to the ringplane, significantly darkens the rings, and causes out-of-plane structures to look anomalously bright and to cast shadows across the rings. These scenes are possible only during the few months before and after Saturn's equinox which occurs only once in about 15 Earth years. Before and after equinox, Cassini's cameras have spotted not only the predictable shadows of some of Saturn's moons, but also the shadows of newly revealed vertical structures in the rings themselves.
The planet's southern hemisphere can be seen through the transparent D ring in the lower right of the image. The rings have been brightened by a factor of 9.5 relative to the planet to enhance visibility.
This view looks toward the northern, unilluminated side of the rings from about 30 degrees above the ringplane.
Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were obtained with the Cassini spacecraft wide-angle camera on July 18, 2009 at a distance of approximately 2.1 million kilometers (1.3 million miles) from Saturn. Image scale is 122 kilometers (76 miles) per pixel.
Image Credit: NASA/JPL/Space Science Institute
Explanation from: http://photojournal.jpl.nasa.gov/catalog/PIA12708