NASA Astronomy Picture of the Day 2016-5

Contemplating the Sun

Have you contemplated your home star recently? Featured here, a Sun partially eclipsed on the top left by the Moon is also seen eclipsed by earthlings contemplating the eclipse below. The spectacular menagerie of silhouettes was taken in 2012 from the Glen Canyon National Recreation Area near Page, Arizona, USA, where park rangers and astronomers expounded on the unusual event to interested gatherers. Also faintly visible on the Sun's disk, just to the lower right of the dark Moon's disk, is a group of sunspots. Although a partial solar eclipse by the Moon is indeed a good chance to contemplate the Sun, a great chance -- and one that is significantly more rare -- will occur next week when the Sun undergoes a partial eclipse by the planet Mercury.

Crossing Mars

Where is NASA's rover Curiosity going on Mars? Its geographical goals are on the slopes of Mount Sharp, whose peak is seen in the background on the right. A key scientific goal, however, remains to better assess when and where conditions on Mars were once suitable for life, in particular microbial life. To further this goal, Curiosity was directed to cross the rugged terrain of Nautkluft Plateau, visible in the featured image on the foreground left. Curiosity is crossing toward smoother uphill sites with rocks containing hematite and sulfates, sites that could give the rolling rover new clues on how long this part of Mars was wet -- and hence more favorable for life -- before drying out. Of recent concern, however, is Curiosity's aluminum wheels, which are showing increasing signs of wear. Although already fulfilling the goals of its two year study, Curiosity's mission has been extended as it continues to uncover valuable information about the extraordinary past of Mars, the next planet out from the Sun from Earth.

Aurora over Sweden

It was bright and green and stretched across the sky. This striking aurora display was captured last month just outside of Östersund, Sweden. Six photographic fields were merged to create the featured panorama spanning almost 180 degrees. Particularly striking aspects of this aurora include its sweeping arc-like shape and its stark definition. Lake Storsjön is seen in the foreground, while several familiar constellations and the star Polaris are visible through the aurora, far in the background. Coincidently, the aurora appears to avoid the Moon visible on the lower left. The aurora appeared a day after a large hole opened in the Sun's corona allowing particularly energetic particles to flow out into the Solar System. The green color of the aurora is caused by oxygen atoms recombining with ambient electrons high in the Earth's atmosphere.

A Mercury Transit Sequence

This coming Monday, Mercury will cross the face of the Sun, as seen from Earth. Called a transit, the last time this happened was in 2006. Because the plane of Mercury's orbit is not exactly coincident with the plane of Earth's orbit, Mercury usually appears to pass over or under the Sun. The above time-lapse sequence, superimposed on a single frame, was taken from a balcony in Belgium shows the entire transit of 2003 May 7. The solar crossing lasted over five hours, so that the above 23 images were taken roughly 15 minutes apart. The north pole of the Sun, the Earth's orbit, and Mercury's orbit, although all different, all occur in directions slightly above the left of the image. Near the center and on the far right, sunspots are visible. After Monday, the next transit of Mercury will occur in 2019. NASA Coverage: 2016 May 9 Mercury Transit of the Sun

The SONG and the Hunter

Near first quarter, the Moon in March lights this snowy, rugged landscape, a view across the top of Tenerife toward La Palma in the Canary Islands Spanish archipelago. The large Teide volcano, the highest point in Spain, looms over the horizon. Shining above are familiar bright stars of Orion, the Hunter. Adding to the dreamlike scene is the 1 meter diameter prototype telescope of the global network project called the Stellar Observations Network Group or SONG. The SONG's fully robotic observatory was captured during the 30 second exposure while the observatory dome, with slit open, was rotated across the field of view.

NGC 7023: The Iris Nebula

These cosmic clouds have blossomed 1,300 light-years away, in the fertile starfields of the constellation Cepheus. Called the Iris Nebula, NGC 7023 is not the only nebula to evoke the imagery of flowers, though. Still, this deep telescopic image shows off the Iris Nebula's range of colors and symmetries, embedded in surrounding fields of interstellar dust. Within the Iris itself, dusty nebular material surrounds a hot, young star. The dominant color of the brighter reflection nebula is blue, characteristic of dust grains reflecting starlight. Central filaments of the reflection nebula glow with a faint reddish photoluminesence as some dust grains effectively convert the star's invisible ultraviolet radiation to visible red light. Infrared observations indicate that this nebula contains complex carbon molecules known as PAHs. The pretty blue petals of the Iris Nebula span about six light-years. The colorful field-of-view stretches almost five Full Moons across the sky.

Three Worlds for TRAPPIST-1

Three new found worlds orbit the ultracool dwarf star TRAPPIST-1, a mere 40 light-years away. Their transits were first detected by the Belgian robotic TRAnsiting Planets and Planetesimals Small Telescope, TRAPPIST, at ESO's La Silla Observatory in Chile. The newly discovered exoplanets are all similar in size to Earth. Because they orbit very close to their faint, tiny star they could also have regions where surface temperatures allow for the presence of liquid water, a key ingredient for life. Their tantalizing proximity to Earth makes them prime candidates for future telescopic explorations of the atmospheres of these potentially habitable planets. All three worlds appear in this artist's vision, an imagined scene near the horizon of the system's outermost planet. Of course, the inner planet is transiting the dim, red, nearly Jupiter-sized parent star.

Mercury's Transit: An Unusual Spot on the Sun

What's that dot on the Sun? If you look closely, it is almost perfectly round. The dot is the result of an unusual type of solar eclipse that occurred in 2006. Usually it is the Earth's Moon that eclipses the Sun. This time, the planet Mercury took a turn. Like the approach to New Moon before a solar eclipse, the phase of Mercury became a continually thinner crescent as the planet progressed toward an alignment with the Sun. Eventually the phase of Mercury dropped to zero and the dark spot of Mercury crossed our parent star. The situation could technically be labeled a Mercurian annular eclipse with an extraordinarily large ring of fire. From above the cratered planes of the night side of Mercury, the Earth appeared in its fullest phase. Hours later, as Mercury continued in its orbit, a slight crescent phase appeared again. This was ten years ago -- the next Mercurian solar eclipse will occur tomorrow. NASA Coverage: Tomorrow's Transit of Mercury across the Sun

Webb Telescope Mirror Rises after Assembly

Move over Hubble -- here comes the James Webb Space Telescope (JWST). JWST promises to be the new most powerful telescope in space. In the last month, the 18-segment gold-plated primary mirror for JWST was unveiled. In the featured time-lapse video taken last week, the 6.5-meter diameter mirror was raised to a vertical position. The dramatic 30-second sequence shows NASA engineers monitoring the test as room lights glint brightly off the mirror's highly reflective surface. The beryllium mirrors have been coated with a thin film of gold to make them more reflective to infrared light. The science goals of JWST include studying the workings of the early universe and the properties of planets orbiting nearby stars. Because of the mirror's great size, it will be folded for launch and then, assuming all goes as planned, dramatically unfolded again in space. The JWST, a joint mission of the space agencies of the USA, Europe, and Canada, is currently scheduled to be launched in late 2018. NASA Coverage: Today's Transit of Mercury across the Sun

Saturn and Mars visit Milky Way Star Clouds

Planets, stars, nebulas and a galaxy -- this impressive image has them all. Closest to home are the two planets Mars (right) and Saturn (center), visible as the two bright orange spots in the upper half of the featured image. On the central right are the colorful Rho Ophiuchus star clouds featuring the bright orange star Antares lined up below Mars. These interstellar clouds contain both red emission nebulas and blue reflection nebulas. At the top right of the image is the Blue Horsehead reflection nebula. On the lower left are many dark absorption nebulas that extend from the central band of our Milky Way Galaxy. The featured deep composite was composed of multiple deep exposures taken last month from Brazil. Although you need a telescope to see the nebulosities, Saturn and Mars will remain visible to the unaided eye this month toward the east, just after sunset. Follow APOD on: Facebook, Google Plus, Instagram, or Twitter

A Mercury Transit Music Video from SDO

What's that small black dot moving across the Sun? Mercury. Possibly the clearest view of Mercury crossing in front of the Sun earlier this week was from Earth orbit. The Solar Dynamics Observatory obtained an uninterrupted vista recording it not only in optical light but also in bands of ultraviolet light. Featured here is a composite movie of the crossing set to music. Although the event might prove successful scientifically for better determining components of Mercury' ultra-thin atmosphere, the event surely proved successful culturally by involving people throughout the world in observing a rare astronomical phenomenon. Many spectacular images of this Mercury transit from around (and above) the globe are being proudly displayed. Astrophysicists: Browse 1,250+ codes in the Astrophysics Source Code Library

A Transit of Mercury

On May 9, the diminutive disk of Mercury spent about seven and a half hours crossing in front of the Sun as viewed from the general vicinity of Earth. It was the third of 14 transits of the Solar System's innermost planet in the 21st century. Captured from Fulham, London, England, planet Earth the tiny silhouette shares the enormous solar disk with prominences, filaments, and active regions in this sharp image. But Mercury's round disk (left of center) appears to be the only dark spot, despite the planet-sized sunspots scattered across the Sun. Made with an H-alpha filter that narrowly transmits the red light from hydrogen atoms, the image emphasizes the chromosphere, stretching above the photosphere or normally visible solar surface. In H-alpha pictures of the chromosphere, normally dark sunspot regions are dominated by bright splotches called plages.

ISS and Mercury Too

Transits of Mercury are relatively rare. Monday's leisurely 7.5 hour long event was only the 3rd of 14 Mercury transits in the 21st century. If you're willing to travel, transits of the International Space Station can be more frequent though, and much quicker. This sharp video frame composite was taken from a well-chosen location in Philadelphia, USA. It follows the space station, moving from upper right to lower left, as it crossed the Sun's disk in 0.6 seconds. Mercury too is included as the small, round, almost stationary silhouette just below center. In apparent size, the International Space Station looms larger from low Earth orbit, about 450 kilometers from Philadelphia. Mercury was about 84 million kilometers away. (Editor's note: The stunning video includes another double transit, Mercury and a Pilatus PC12 aircraft. Even quicker than the ISS to cross the Sun, the aircraft was about 1 kilometer away.)

Falcon 9 and Milky Way

On May 6, the after midnight launch of a SpaceX Falcon 9 rocket lit up dark skies over Merritt Island, planet Earth. Its second stage bound for Earth orbit, the rocket's arc seems to be on course for the center of the Milky Way in this pleasing composite image looking toward the southeast. Two consecutive exposures made with camera fixed to a tripod were combined to follow rocket and home galaxy. A 3 minute long exposure at low sensitivity allowed the rocket's first stage burn to trace the bright orange arc and a 30 second exposure at high sensitivity captured the stars and the faint Milky Way. Bright orange Mars dominates the starry sky at the upper right. A few minutes later, booster engines were restarted and the Falcon 9's first stage headed for a landing on the autonomous spaceport drone ship Of Course I Still Love You, patiently waiting in the Atlantic 400 miles east of the Cape Canaveral launch site.

Milky Way Over Quiver Tree Forest

In front of a famous background of stars and galaxies lies some of Earth's more unusual trees. Known as quiver trees, they are actually succulent aloe plants that can grow to tree-like proportions. The quiver tree name is derived from the historical usefulness of their hollowed branches as dart holders. Occurring primarily in southern Africa, the trees pictured in the above 16-exposure composite are in Quiver Tree Forest located in southern Namibia. Some of the tallest quiver trees in the park are estimated to be about 300 years old. Behind the trees is light from the small town of Keetmanshoop, Namibia. Far in the distance, arching across the background, is the majestic central band of our Milky Way Galaxy. Even further in the distance, visible on the image left, are the Large and Small Magellanic Clouds, smaller satellite galaxies of the Milky Way that are prominent in the skies of Earth's southern hemisphere.

Clouds of the Carina Nebula

What forms lurk in the mists of the Carina Nebula? The dark ominous figures are actually molecular clouds, knots of molecular gas and dust so thick they have become opaque. In comparison, however, these clouds are typically much less dense than Earth's atmosphere. Featured here is a detailed image of the core of the Carina Nebula, a part where both dark and colorful clouds of gas and dust are particularly prominent. The image was captured last month from Siding Spring Observatory in Australia. Although the nebula is predominantly composed of hydrogen gas -- here colored green, the image was assigned colors so that light emitted by trace amounts of sulfur and oxygen appear red and blue, respectively. The entire Carina Nebula, cataloged as NGC 3372, spans over 300 light years and lies about 7,500 light-years away in the constellation of Carina. Eta Carinae, the most energetic star in the nebula, was one of the brightest stars in the sky in the 1830s, but then faded dramatically.

The Orion Nebula in Visible and Infrared

The Great Nebula in Orion is a colorful place. Visible to the unaided eye, it appears as a small fuzzy patch in the constellation of Orion. Long exposure, multi-wavelength images like this, however, show the Orion Nebula to be a busy neighborhood of young stars, hot gas, and dark dust. This digital composite features not only three colors of visible light but four colors of infrared light taken by NASA's orbiting Spitzer Space Telescope as well. The power behind much of the Orion Nebula (M42) is the Trapezium - four of the brightest stars in the nebula. Many of the filamentary structures visible are actually shock waves - fronts where fast moving material encounters slow moving gas. The Orion Nebula spans about 40 light years and is located about 1500 light years away in the same spiral arm of our Galaxy as the Sun. Follow APOD on: Facebook, Google Plus, Instagram, or Twitter

Halo from Atacama

Influenced by the strong Pacific El Nino, cloudy skies have more often come to Chile's high Atacama Desert this season, despite its reputation as an astronomer's paradise. Located in one of the driest, darkest places on planet Earth, domes of the region's twin 6.5 meter Magellan telescopes of Carnegie Las Campanas Observatory were closed on May 13. Still, a first quarter Moon and bright stars shine through in this panoramic night skyscape, the lunar disk surrounded by a beautiful, bright halo. The angular radius of the halo is 22 degrees. Not determined by the brightness or phase of the Moon itself, the angle is set by the hexagonal geometry of atmospheric ice crystals that reflect and refract the moonlight. On that night, the brilliant star just inside the halo's radius was really planet Jupiter. The brightest star flanking the halo to the far left is Canopus, with Arcturus on the halo's right. Participate: Take an Aesthetics & Astronomy Survey

The Surface of Europa

An enhanced-color view, this image covers a 350 by 750 kilometer swath across the surface of Jupiter's tantalizing moon Europa. The close-up combines high-resolution image data with lower resolution color data from observations made in 1998 by the Galileo spacecraft. Smooth ice plains, long fractures, and jumbled blocks of chaos terrain are thought to hide a deep ocean of salty liquid water beneath. Though the ice-covered alien ocean world is outside the Solar System's habitable zone, new studies show the potential chemistry driving its oxygen and hydrogen production, a key indicator of the energy available for life, could produce amounts comparable in scale to planet Earth. Hydrogen would be generated by chemical reactions of the salty water in contact with the rocky ocean floor. Oxygen and other compounds that react with hydrogen would come from Europa's surface. There water ice molecules would be split apart by the intense flux of high-energy radiation from Jupiter and cycled into the Europan ocean from above. Participate: Take an Aesthetics & Astronomy Survey

3D Mercury Transit

On May 9, innermost planet Mercury crossed IN FRONT of the Sun. Though pictures project the event in only two dimensions, a remarkable three dimensional perspective on the transit is possible by free viewing this stereo pair. The images were made 23 minutes apart and rotated so that Mercury's position shifts horizontally between the two. As a result, Mercury's orbital motion produced an exaggerated parallax simulating binocular vision. Between the two exposures, the appropriately named planet's speedy 47.4 kilometer per second orbital velocity actually carried it over 65,000 kilometers. Taken first, the left image is intended for the right eye, so a cross-eyed view is needed to see Mercury's tiny silhouette suspended in the foreground. Try it. Merging the text below the images helps. Participate: Take an Aesthetics & Astronomy Survey

Milky Way and Planets Near Opposition

In this early May night skyscape, a mountain road near Bursa, Turkey seems to lead toward bright planets Mars and Saturn and the center of our Milky Way Galaxy, a direction nearly opposite the Sun in planet Earth's sky. The brightest celestial beacon on the scene, Mars, reaches its opposition tonight and Saturn in early June. Both will remain nearly opposite the Sun, up all night and close to Earth for the coming weeks, so the time is right for good telescopic viewing. Mars and Saturn form the tight celestial triangle with red giant star Antares just right of the Milky Way's central bulge. But tonight the Moon is also at opposition. Easy to see near bright Mars and Saturn, the Full Moon's light will wash out the central Milky Way's fainter starlight though, even in dark mountain skies. Participate: Take an Aesthetics & Astronomy Survey

LL Orionis: When Cosmic Winds Collide

What created this great arc in space? This arcing, graceful structure is actually a bow shock about half a light-year across, created as the wind from young star LL Orionis collides with the Orion Nebula flow. Adrift in Orion's stellar nursery and still in its formative years, variable star LL Orionis produces a wind more energetic than the wind from our own middle-aged sun. As the fast stellar wind runs into slow moving gas a shock front is formed, analogous to the bow wave of a boat moving through water or a plane traveling at supersonic speed. The slower gas is flowing away from the Orion Nebula's hot central star cluster, the Trapezium, located off the lower right hand edge of the picture. In three dimensions, LL Ori's wrap-around shock front is shaped like a bowl that appears brightest when viewed along the "bottom" edge. The complex stellar nursery in Orion shows a myriad of similar fluid shapes associated with star formation, including the bow shock surrounding a faint star at the upper right. Part of a mosaic covering the Great Nebula in Orion, this composite color image was recorded in 1995 by the Hubble Space Telescope. Follow APOD on: Facebook, Google Plus, Instagram, or Twitter

Inside a Daya Bay Antineutrino Detector

Why is there more matter than antimatter in the Universe? To better understand this facet of basic physics, energy departments in China and the USA led in the creation of the Daya Bay Reactor Neutrino Experiment. Located under thick rock about 50 kilometers northeast of Hong Kong, China, eight Daya Bay detectors monitor antineutrinos emitted by six nearby nuclear reactors. Featured here, a camera looks along one of the Daya Bay detectors, imaging photon sensors that pick up faint light emitted by antineutrinos interacting with fluids in the detector. Early results indicate an unexpectedly high rate of one type of antineutrino changing into another, a rate which, if confirmed, could imply the existence of a previously undetected type of neutrino as well as impact humanity's comprehension of fundamental particle reactions that occurred within the first few seconds of the Big Bang. Astrophysicists: Browse 1,250+ codes in the Astrophysics Source Code Library

Milky Way Over the Spanish Peaks

That's not lightning, and it did not strike between those mountains. The diagonal band is actually the central band of our Milky Way Galaxy, while the twin peaks are actually called the Spanish Peaks -- but located in Colorado, USA. Although each Spanish peak is composed of a slightly different type of rock, both are approximately 25 million years old. This serene yet spirited image composite was meticulously created by merging a series of images all taken from the same location on one night and early last month. In the first series of exposures, the background sky was built up, with great detail being revealed in the Milky Way dust lanes as well as the large colorful region surrounding the star Rho Ophiuchus just right of center. One sky image, though, was taken using a fogging filter so that brighter stars would appear more spread out and so more prominent. As a bonus, the planets Mars and Saturn are placed right above peaks and make an orange triangle with the bright star Antares. Later that night, after the moonrise, the Moon itself naturally illuminated the snow covered mountain tops.

NGC 5078 and Friends

This sharp telescopic field of view holds two bright galaxies. Barred spiral NGC 5101 (top right) and nearly edge-on system NGC 5078 are separated on the sky by about 0.5 degrees or about the apparent width of a full moon. Found within the boundaries of the serpentine constellation Hydra, both are estimated to be around 90 million light-years away and similar in size to our own large Milky Way galaxy. In fact, if they both lie at the same distance their projected separation would be only 800,000 light-years or so. That's easily less than half the distance between the Milky Way and the Andromeda Galaxy. NGC 5078 is interacting with a smaller companion galaxy, cataloged as IC 879, seen just left of the larger galaxy's bright core. Even more distant background galaxies are scattered around the colorful field. Some are even visible right through the face-on disk of NGC 5101. But the prominent spiky stars are in the foreground, well within our own Milky Way.

IC 5067 in the Pelican Nebula

The prominent ridge of emission featured in this sharp, colorful skyscape is cataloged as IC 5067. Part of a larger emission nebula with a distinctive shape, popularly called The Pelican Nebula, the ridge spans about 10 light-years following the curve of the cosmic pelican's head and neck. This false-color view also translates the pervasive glow of narrow emission lines from atoms in the nebula to a color palette made popular in Hubble Space Telescope images of star forming regions. Fantastic, dark shapes inhabiting the 1/2 degree wide field are clouds of cool gas and dust sculpted by the winds and radiation from hot, massive stars. Close-ups of some of the sculpted clouds show clear signs of newly forming stars. The Pelican Nebula, itself cataloged as IC 5070, is about 2,000 light-years away. To find it, look northeast of bright star Deneb in the high flying constellation Cygnus.

The Great Carina Nebula

A jewel of the southern sky, the Great Carina Nebula, also known as NGC 3372, spans over 300 light-years, one of our galaxy's largest star forming regions. Like the smaller, more northerly Great Orion Nebula, the Carina Nebula is easily visible to the unaided eye, though at a distance of 7,500 light-years it is some 5 times farther away. This gorgeous telescopic close-up reveals remarkable details of the region's central glowing filaments of interstellar gas and obscuring cosmic dust clouds. The field of view is over 50 light-years across. The Carina Nebula is home to young, extremely massive stars, including the stars of open cluster Trumpler 14 (below and right of center) and the still enigmatic variable Eta Carinae, a star with well over 100 times the mass of the Sun. Eta Carinae is the brightest star, seen here just above the dusty Keyhole Nebula (NGC 3324). While Eta Carinae itself maybe on the verge of a supernova explosion, X-ray images indicate that the Great Carina Nebula has been a veritable supernova factory.

Cat's Eye Wide and Deep

The Cat's Eye Nebula (NGC 6543) is one of the best known planetary nebulae in the sky. Its more familiar outlines are seen in the brighter central region of the nebula in this impressive wide-angle view. But the composite image combines many short and long exposures to also reveal an extremely faint outer halo. At an estimated distance of 3,000 light-years, the faint outer halo is over 5 light-years across. Planetary nebulae have long been appreciated as a final phase in the life of a sun-like star. More recently, some planetary nebulae are found to have halos like this one, likely formed of material shrugged off during earlier episodes in the star's evolution. While the planetary nebula phase is thought to last for around 10,000 years, astronomers estimate the age of the outer filamentary portions of this halo to be 50,000 to 90,000 years. Visible on the left, some 50 million light-years beyond the watchful planetary nebula, lies spiral galaxy NGC 6552.

Valles Marineris: The Grand Canyon of Mars

Mars will look good in Earth's skies over the next few days -- but not this good. To get a view this amazing, a spacecraft had to actually visit the red planet. Running across the image center, though, is one the largest canyons in the Solar System. Named Valles Marineris, the grand valley extends over 3,000 kilometers long, spans as much as 600 kilometers across, and delves as much as 8 kilometers deep. By comparison, the Earth's Grand Canyon in Arizona, USA is 800 kilometers long, 30 kilometers across, and 1.8 kilometers deep. The origin of the Valles Marineris remains unknown, although a leading hypothesis holds that it started as a crack billions of years ago as the planet cooled. Several geologic processes have been identified in the canyon. The featured mosaic was created from over 100 images of Mars taken by Viking Orbiters in the 1970s. Tomorrow, Mars and Earth will pass the closest in 11 years, resulting in the red planet being quite noticeable toward the southeast after sunset.

Galaxy Evolution Tracking Animation

How did the universe evolve from such a smooth beginning? To help understand, computational cosmologists and NASA produced the featured time-lapse animated video depicting a computer simulation of part of the universe. The 100-million light-year simulation starts about 20 million years after the Big Bang and runs until the present. After a smooth beginning, gravity causes clumps of matter to form into galaxies which immediately begin falling toward each other. Soon, many of them condense into long filaments while others violently merge into a huge and hot cluster of galaxies. Investigating of potential universe attributes in simulations like this have helped shape the engineering design the James Webb Space Telescope, currently scheduled for launch in late 2018.

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