NASA Astronomy Picture of the Day 2017-1

A Full Sky Aurora Over Norway

Higher than the highest building, higher than the highest mountain, higher than the highest airplane, lies the realm of the aurora. Auroras rarely reach below 60 kilometers, and can range up to 1000 kilometers. Aurora light results from energetic electrons and protons striking molecules in the Earth's atmosphere. Frequently, when viewed from space, a complete aurora will appear as a circle around one of the Earth's magnetic poles. The featured wide-angle image, horizontally compressed, captured an unexpected auroral display that stretched across the sky five years ago over eastern Norway.

Comet 45P Returns

An old comet has returned to the inner Solar System. Not only is Comet 45P/Honda–Mrkos–Pajdušáková physically ancient, it was first discovered 13 orbits ago in 1948. Comet 45P spends most of its time out near the orbit of Jupiter and last neared the Sun in 2011. Over the past few months, however, Comet 45P's new sunward plummet has brightened it considerably. Two days ago, the comet passed the closest part of its orbit to the Sun. The comet is currently visible with binoculars over the western horizon just after sunset, not far from the much brighter planet Venus. Pictured, Comet 45P was captured last week sporting a long ion tail with impressive structure. Comet 45P will pass relatively close to the Earth early next month. APOD Lecture: Friday, Jan. 6, Amateur Astronomers Association of New York City

Pandora Close-up at Saturn

What do the craters of Saturn's small moon Pandora look like up close? To help find out, NASA sent the robotic Cassini spacecraft, now orbiting Saturn, past the unusual moon two weeks ago. The highest resolution image of Pandora ever taken was then captured from about 40,000 kilometers out and is featured here. Structures as small as 300 meters can be discerned on 80-kilometer wide Pandora. Craters on Pandora appear to be covered over by some sort of material, providing a more smooth appearance than sponge-like Hyperion, another small moon of Saturn. Curious grooves and ridges also appear to cross the surface of the small moon. Pandora is partly interesting because, along with its companion moon Prometheus, it helps shepherd the particles of Saturn's F ring into a distinct ring.

Clouds of Andromeda

The beautiful Andromeda Galaxy is often imaged by planet Earth-based astronomers. Also known as M31, the nearest large spiral galaxy is a familiar sight with dark dust lanes, bright yellowish core, and spiral arms traced by blue starlight. A mosaic of well-exposed broad and narrow-band image data, this colorful, premier portrait of our neighboring island universe offers strikingly unfamiliar features though, faint reddish clouds of glowing ionized hydrogen gas in the same wide field of view. Still, the ionized hydrogen clouds likely lie in the foreground of the scene, well within our Milky Way Galaxy. They could be associated with the pervasive, dusty interstellar cirrus clouds scattered hundreds of light-years above our own galactic plane. If they were located at the 2.5 million light-year distance of the Andromeda Galaxy they would be enormous, since the Andromeda Galaxy itself is 200,000 or so light-years across.

Peculiar Galaxies of Arp 273

The spiky stars in the foreground of this sharp cosmic portrait are well within our own Milky Way Galaxy. The two eye-catching galaxies lie far beyond the Milky Way, at a distance of over 300 million light-years. Their distorted appearance is due to gravitational tides as the pair engage in close encounters. Cataloged as Arp 273 (also as UGC 1810), the galaxies do look peculiar, but interacting galaxies are now understood to be common in the universe. In fact, the nearby large spiral Andromeda Galaxy is known to be some 2 million light-years away and approaching the Milky Way. Arp 273 may offer an analog of their far future encounter. Repeated galaxy encounters on a cosmic timescale can ultimately result in a merger into a single galaxy of stars. From our perspective, the bright cores of the Arp 273 galaxies are separated by only a little over 100,000 light-years.

New York Harbor Moonset

Moonset on January 1 is captured in this sea and night sky snapshot from the port city of New York. Its warm moonlight shining through haze and thin clouds, this New Year's Moon was about 3 days old, in a waxing crescent phase. The visible lunar disk is about 10 percent illuminated. Also easy to spot in hazy urban skies, Venus blazes forth over the western horizon, begining the year as Earth's evening star. Like the Moon, Venus goes through a range of phases as seen from planet Earth. As the year began, telescopic views of the brilliant inner planet's disk would show it about 50 percent illuminated, growing into a larger but thinner crescent by early March. New York Harbor's welcoming beacon, the Statue of Liberty, anchors a terrestrial corner of the night's triangle at the far left.

Sharpless 249 and the Jellyfish Nebula

Normally faint and elusive, the Jellyfish Nebula is caught in this alluring telescopic mosaic. The scene is anchored below by bright star Eta Geminorum, at the foot of the celestial twin, while the Jellyfish Nebula is the brighter arcing ridge of emission with tentacles dangling below and left of center. In fact, the cosmic jellyfish is part of bubble-shaped supernova remnant IC 443, the expanding debris cloud from a massive star that exploded. Light from the explosion first reached planet Earth over 30,000 years ago. Like its cousin in astrophysical waters the Crab Nebula supernova remnant, the Jellyfish Nebula is known to harbor a neutron star, the remnant of the collapsed stellar core. An emission nebula cataloged as Sharpless 249 fills the field at the upper right. The Jellyfish Nebula is about 5,000 light-years away. At that distance, this narrowband composite image presented in the Hubble Palette would be about 300 light-years across.

IC 4406: A Seemingly Square Nebula

How can a round star make a square nebula? This conundrum comes to light when studying planetary nebulae like IC 4406. Evidence indicates that IC 4406 is likely a hollow cylinder, with its square appearance the result of our vantage point in viewing the cylinder from the side. Were IC 4406 viewed from the top, it would likely look similar to the Ring Nebula. This representative-color picture is a composite made by combining images taken by the Hubble Space Telescope in 2001 and 2002. Hot gas flows out the ends of the cylinder, while filaments of dark dust and molecular gas lace the bounding walls. The star primarily responsible for this interstellar sculpture can be found in the planetary nebula's center. In a few million years, the only thing left visible in IC 4406 will be a fading white dwarf star.

In the Center of Spiral Galaxy NGC 5033

What's happening in the center of spiral NGC 5033? Many things -- some circular, some energetic, and some not well understood. NGC 5033 is known as a Seyfert galaxy because of the great activity seen in its nucleus. Bright stars, dark dust, and interstellar gas all swirl quickly around a galactic center that appears slightly offset from a supermassive black hole. This offset is thought to be the result of NGC 5033 merging with another galaxy sometime in the past billion years. The featured image was taken by the Hubble Space Telescope in 2005. NGC 5033 spans about 100,000 light years and is so far away that we see it only as it existed about 40 million years ago.

Sentinels of a Northern Sky

Who guards the north? The featured picture was taken last March in Finnish Lapland where weather can include sub-freezing temperatures and driving snow. Surreal landscapes sometimes result, where white alien-looking sentinels seem to patrol the landscape. In actuality though, the aliens are snow-covered trees, and the red hut they seem to be guarding is an outhouse. Far in the distance, behind this uncommon Earthly vista, is a beautiful night sky which includes a green aurora, bright stars, and streaks of orbiting satellites. Of course, in the spring, the trees thaw and Lapland looks much different.

Mimas, Crater, and Mountain

Mimas is an icy, crater-pocked moon of Saturn a mere 400 kilometers (250 miles) in diameter. Its largest crater Herschel is nearly 140 kilometers wide. About a third the diameter of Mimas itself, Herschel crater gives the small moon an ominous appearance, especially for scifi fans of the Death Star battlestation of Star Wars fame. In fact, only a slightly bigger impact than the one that created such a large crater on a small moon could have destroyed Mimas entirely. In this Cassini image from October 2016, the anti-Saturn hemisphere of the synchronously rotating moon is bathed in sunlight, its large crater near the right limb. Casting a long shadow across the crater floor, Herschel's central mountain peak is nearly as tall as Mount Everest on planet Earth.

Edge-On NGC 891

Large spiral galaxy NGC 891 spans about 100 thousand light-years and is seen almost exactly edge-on from our perspective. In fact, about 30 million light-years distant in the constellation Andromeda, NGC 891 looks a lot like our Milky Way. At first glance, it has a flat, thin, galactic disk of stars and a central bulge cut along the middle by regions of dark obscuring dust. But remarkably apparent in NGC 891's edge-on presentation are filaments of dust that extend hundreds of light-years above and below the center line. The dust has likely been blown out of the disk by supernova explosions or intense star formation activity. Fainter galaxies can also be seen near the edge-on disk in this deep portrait of NGC 891. (Editor's Note: The NGC 891 image used in today's APOD posting has been replaced and the credit corrected to indicate the author of the original work.)

When Mars met Neptune

On January 1, a Mars-assisted viewing opportunity allowed binocular-equipped skygazers to cross an ice giant off their life list. Remarkably, the line-of-sight to the bright Red Planet could guide you to within 0.02 degrees of a faint, pale Neptune in Earth's night skies. Taken within 3 hours of their closest conjunction, these panels capture the odd couple's appearance in skies over Brisbane, Australia. A wide field view includes the new year's slender crescent moon near the western horizon and Venus as the brilliant evening star. Mars and Neptune are indicated at the upper right. The two inset magnified views were taken with the same telephoto lens and so do show the Mars-Neptune conjunction and the apparent size of the crescent moon at the same scale. This week Neptune hangs out near Venus on the western sky.

Stardust in the Perseus Molecular Cloud

Clouds of stardust drift through this deep skyscape. The cosmic scene spans nearly 2 degrees across the Perseus molecular cloud some 850 light-years away. A triangle of dusty nebulae reflecting light from embedded stars is captured in the telescopic field of view. With a characteristic bluish color reflection nebula NGC 1333 is at left, vdB13 at bottom right, and rare yellowish reflection nebula vdB12 lies at the top. Stars are forming in the Perseus molecular cloud, though most are obscured at visible wavelengths by the pervasive dust. Still, hints of contrasting red emission from Herbig-Haro objects, the jets and shocked glowing gas emanating from recently formed stars, are evident in NGC 1333. At the estimated distance of the molecular cloud, legs of the triangle formed by the reflection nebulae would be about 20 light-years long.

The Matter of the Bullet Cluster

What's the matter with the Bullet Cluster? This massive cluster of galaxies (1E 0657-558) creates gravitational lens distortions of background galaxies in a way that has been interpreted as strong evidence for the leading theory: that dark matter exists within. Different recent analyses, though, indicate that a less popular alternative -- modifying gravity-- could explain cluster dynamics without dark matter, and provide a more likely progenitor scenario as well. Currently, the two scientific hypotheses are competing to explain the observations: it's invisible matter versus amended gravity. The duel is dramatic as a clear Bullet-proof example of dark matter would shatter the simplicity of modified gravity theories. For the near future, the battle over the Bullet cluster is likely to continue as new observations, computer simulations, and analyses are completed. The featured image is a Hubble/Chandra/Magellan composite with red depicting the X-rays emitted by hot gas, and blue depicting the suggested separated dark matter distribution.

Geostationary Highway through Orion

Put a satellite in a circular orbit about 42,000 kilometers from the center of the Earth and it will orbit once in 24 hours. Because that matches Earth's rotation period, it is known as a geosynchronous orbit. If that orbit is also in the plane of the equator, the satellite will hang in the sky over a fixed location in a geostationary orbit. As predicted in the 1940s by futurist Arthur C. Clarke, geostationary orbits are in common use for communication and weather satellites, a scenario now well-known to astroimagers. Deep images of the night sky made with telescopes that follow the stars can also pick up geostationary satellites glinting in sunlight still shining far above the Earth's surface. Because they all move with the Earth's rotation against the background of stars, the satellites leave trails that seem to follow a highway across the celestial landscape. The phenomenon was captured last month in this video showing several satellites in geostationary orbit crossing the famous Orion Nebula. Open Science: Browse 1,400+ codes in the Astrophysics Source Code Library

Fly Me to the Moon

No, this is not a good way to get to the Moon. What is pictured is a chance superposition of an airplane and the Moon. The contrail would normally appear white, but the large volume of air toward the setting Sun preferentially knocks away blue light, giving the reflected trail a bright red hue. Far in the distance, to the right of the plane, is the young Moon. This vast world shows only a sliver of itself because the Sun is nearly lined up behind it. Captured two weeks ago, the featured image was framed by an eerie maroon sky, too far from day to be blue, too far from night to be black. Within minutes the impromptu sky show ended. The plane crossed the Moon. The contrail dispersed. The Sun set. The Moon set. The sky faded to black, only to reveal thousands of stars that had been too faint to see through the rustic red din. I Like Data: Help Analyze APOD's Social Media Footprint in 2015

Space Station Vista: Planet and Galaxy

If you could circle the Earth aboard the International Space Station, what might you see? Some amazing vistas, one of which was captured in this breathtaking picture in mid-2015. First, visible at the top, are parts of the space station itself including solar panels. Just below the station is the band of our Milky Way Galaxy, glowing with the combined light of billions of stars, but dimmed in patches by filaments of dark dust. The band of red light just below the Milky Way is airglow -- Earth's atmosphere excited by the Sun and glowing in specific colors of light. Green airglow is visible below the red. Of course that's our Earth below its air, with the terminator between day and night visible near the horizon. As clouds speckle the planet, illumination from a bright lightning bolt is seen toward the lower right. Between work assignments, astronauts from all over the Earth have been enjoying vistas like this from the space station since the year 2000.

The Elephant's Trunk Nebula in Cepheus

Like an illustration in a galactic Just So Story, the Elephant's Trunk Nebula winds through the emission nebula and young star cluster complex IC 1396, in the high and far off constellation of Cepheus. Also known as vdB 142, the cosmic elephant's trunk is over 20 light-years long. This colorful close-up view includes image data from a narrow band filter that transmits the light from ionized hydrogen atoms in the region. The resulting composite highlights the bright swept-back ridges that outline pockets of cool interstellar dust and gas. Such embedded, dark, tendril-shaped clouds contain the raw material for star formation and hide protostars within. Nearly 3,000 light-years distant, the relatively faint IC 1396 complex covers a large region on the sky, spanning over 5 degrees. This dramatic scene spans a 1 degree wide field, about the size of 2 Full Moons.

Layer Cake Sunset

On January 18 a tantalizing sunset was captured in this snapshot. Seemingly sliced into many horizontal layers the Sun shimmered moments before it touched the horizon, setting over the Pacific Ocean as seen from the mountaintop Las Campanas Observatory in Chile. Pink hues of filtered sunlight were created by the long sight-line through the hazy atmosphere. But the remarkable layers correspond to low atmospheric layers of sharply different temperature and density also along the line of sight. Over a long path through each layer the rays of sunlight are refracted strongly and create different images or mirages of sections of the setting Sun. Participate: Take an Aesthetics & Astronomy Survey

Daphnis the Wavemaker

Plunging close to the outer edges of Saturn's rings, on January 16 the Cassini spacecraft captured this closest yet view of Daphnis. About 8 kilometers across and orbiting within the bright ring system's Keeler gap, the small moon is making waves. The 42-kilometer wide outer gap is foreshortened in the image by Cassini's viewing angle. Raised by the influenced of the small moon's weak gravity as it crosses the frame from left to right, the waves are formed in the ring material at the edge of the gap. A faint wave-like trace of ring material is just visible trailing close behind Daphnis. Remarkable details on Daphnis can also be seen, including a narrow ridge around its equator, likely an accumulation of particles from the ring. Participate: Take an Aesthetics & Astronomy Survey

SpaceX Falcon 9 to Orbit

Birds don't fly this high. Airplanes don't go this fast. The Statue of Liberty weighs less. No species other than human can even comprehend what is going on, nor could any human just a millennium ago. The launch of a rocket bound for space is an event that inspires awe and challenges description. Pictured here, a SpaceX Falcon 9 V rocket lifted off through a cloud deck from Cape Canaveral, Florida last July to deliver cargo and supplies to the International Space Station. From a standing start, the 300,000+ kilogram rocket ship lifted its Dragon Capsule up to circle the Earth, where the outside air is too thin to breathe. Rockets bound for space are now launched from somewhere on Earth about once a week. Participate: Take an Aesthetics & Astronomy Survey

Winter Hexagon over Manla Reservoir

If you can find Orion, you might be able to find the Winter Hexagon. The Winter Hexagon involves some of the brightest stars visible, together forming a large and easily found pattern in the winter sky of Earth's northern hemisphere. The stars involved can usually be identified even in the bright night skies of a big city, although here they appeared recently in dark skies above the Manla Reservoir in Tibet, China. The six stars that compose the Winter Hexagon are Aldebaran, Capella, Castor (and Pollux), Procyon, Rigel, and Sirius. Here, the band of our Milky Way Galaxy runs through the center of the Winter Hexagon, while the Pleiades open star cluster is visible just above. The Winter Hexagon asterism engulfs several constellations including much of the iconic steppingstone Orion. Follow APOD on: Facebook, Google Plus, or Twitter

M78 and Orion Dust Reflections

In the vast Orion Molecular Cloud complex, several bright blue nebulas are particularly apparent. Pictured here are two of the most prominent reflection nebulas - dust clouds lit by the reflecting light of bright embedded stars. The more famous nebula is M78, in the image center, cataloged over 200 years ago. To its left is the lesser known NGC 2071. Astronomers continue to study these reflection nebulas to better understand how interior stars form. The Orion complex lies about 1500 light-years distant, contains the Orion and Horsehead nebulas, and covers much of the constellation of Orion. Almost Hyperspace: Random APOD Generator

Cassini's Grand Finale Tour at Saturn

Cassini is being prepared to dive into Saturn. The robotic spacecraft that has been orbiting and exploring Saturn for over a decade will end its mission in September with a spectacular atmospheric plunge. Pictured here is a diagram of Cassini's remaining orbits, each taking about one week. Cassini is scheduled to complete a few months of orbits that will take it just outside Saturn's outermost ring F. Then, in April, Titan will give Cassini a gravitational pull into Proximal orbits, the last of which, on September 15, will impact Saturn and cause the spacecraft to implode and melt. Cassini's Grand Finale orbits are designed to record data and first-ever views from inside the rings -- between the rings and planet -- as well as some small moons interspersed in the rings. Cassini's demise is designed to protect any life that may occur around Saturn or its moons from contamination by Cassini itself. Free Download: APOD 2017 Calendar: NASA Images

GOES-16: Moon over Planet Earth

Launched last November 19 from Cape Canaveral Air Force Station, the satellite now known as GOES-16 can now observe planet Earth from a geostationary orbit 22,300 miles above the equator. Its Advanced Baseline Imager captured this contrasting view of Earth and a gibbous Moon on January 15. The stark and airless Moon is not really the focus of GOES-16, though. Capable of providing a high resolution full disk image of Earth every 15 minutes in 16 spectral channels, the new generation satellite's instrumentation is geared to provide sharper, more detailed views of Earth's dynamic weather systems and enable more accurate weather forecasting. Like previous GOES weather satellites, GOES-16 will use the moon over our fair planet as a calibration target. Participate: Take an Aesthetics & Astronomy Survey

Venus Through Water Drops

Now the brilliant "star" in planet Earth's evening skies, Venus is captured in this creative astrophotograph. Taken with a close-focusing lens on January 18 from Milton Keynes, UK, it shows multiple images of the sky above the western horizon shortly after sunset. The images were created by water drops on a glass pane fixed to a tree. Surface tension has drawn the water drops into simple lens-like shapes. Refracting light, the drops create images that are upside-down, so the scene has been rotated to allow comfortable right-side up viewing of a macro-multiple-skyscape. Participate: Take an Aesthetics & Astronomy Survey

N159 in the Large Magellanic Cloud

Over 150 light-years across, this cosmic maelstrom of gas and dust is not too far away. It lies south of the Tarantula Nebula in our satellite galaxy the Large Magellanic Cloud a mere 180,000 light-years distant. Massive stars have formed within. Their energetic radiation and powerful stellar winds sculpt the gas and dust and power the glow of this HII region, entered into the Henize catalog of emission stars and nebulae in the Magellanic Clouds as N159. The bright, compact, butterfly-shaped nebula above and left of center likely contains massive stars in a very early stage of formation. Resolved for the first time in Hubble images, the compact blob of ionized gas has come to be known as the Papillon Nebula. Participate: Take an Aesthetics & Astronomy Survey

Red Aurora Over Australia

Why would the sky glow red? Aurora. A solar storm in 2012, emanating mostly from active sunspot region 1402, showered particles on the Earth that excited oxygen atoms high in the Earth's atmosphere. As the excited element's electrons fell back to their ground state, they emitted a red glow. Were oxygen atoms lower in Earth's atmosphere excited, the glow would be predominantly green. Pictured here, this high red aurora is visible just above the horizon last week near Flinders, Victoria, Australia. The sky that night, however, also glowed with more familiar but more distant objects, including the central disk of our Milky Way Galaxy on the left, and the neighboring Large and Small Magellanic Cloud galaxies on the right. A time-lapse video highlighting auroras visible that night puts the picturesque scene in context. Why the sky did not also glow green remains unknown.

The Cat's Eye Nebula from Hubble

To some, it may look like a cat's eye. The alluring Cat's Eye nebula, however, lies three thousand light-years from Earth across interstellar space. A classic planetary nebula, the Cat's Eye (NGC 6543) represents a final, brief yet glorious phase in the life of a sun-like star. This nebula's dying central star may have produced the simple, outer pattern of dusty concentric shells by shrugging off outer layers in a series of regular convulsions. But the formation of the beautiful, more complex inner structures is not well understood. Seen so clearly in this digitally reprocessed Hubble Space Telescope image, the truly cosmic eye is over half a light-year across. Of course, gazing into this Cat's Eye, astronomers may well be seeing the fate of our sun, destined to enter its own planetary nebula phase of evolution ... in about 5 billion years.

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