NASA Astronomy Picture of the Day 2019-5

The Cat's Eye Nebula in Optical and X-ray

To some it looks like a cat's eye. To others, perhaps like a giant cosmic conch shell. It is actually one of brightest and most highly detailed planetary nebula known, composed of gas expelled in the brief yet glorious phase near the end of life of a Sun-like star. This nebula's dying central star may have produced the outer circular concentric shells by shrugging off outer layers in a series of regular convulsions. The formation of the beautiful, complex-yet-symmetric inner structures, however, is not well understood. The featured image is a composite of a digitally sharpened Hubble Space Telescope image with X-ray light captured by the orbiting Chandra Observatory. The exquisite floating space statue spans over half a light-year across. Of course, gazing into this Cat's Eye, humanity may well be seeing the fate of our sun, destined to enter its own planetary nebula phase of evolution ... in about 5 billion years.

Manicouagan Impact Crater from Space

Orbiting 400 kilometers above Quebec, Canada, planet Earth, the International Space Station Expedition 59 crew captured this snapshot of the broad St. Lawrence River and curiously circular Lake Manicouagan on April 11. Right of center, the ring-shaped lake is a modern reservoir within the eroded remnant of an ancient 100 kilometer diameter impact crater. The ancient crater is very conspicuous from orbit, a visible reminder that Earth is vulnerable to rocks from space. Over 200 million years old, the Manicouagan crater was likely caused by the impact of a rocky body about 5 kilometers in diameter. Currently, there is no known asteroid with a significant probability of impacting Earth in the next century. But a fictional scenario to help practice for an asteroid impact is on going at the 2019 IAA Planetary Defense Conference.

Clouds of the Large Magellanic Cloud

The Large Magellanic Cloud (LMC) is an alluring sight in southern skies. But this deep and detailed telescopic view, over 10 months in the making, goes beyond what is visible to most circumnavigators of planet Earth. Spanning over 5 degrees or 10 full moons, the 4x4 panel mosaic was constructed from 3900 frames with a total of 1,060 hours of exposure time in both broadband and narrowband filters. The narrowband filters are designed to transmit only light emitted by sulfur, hydrogen, and oxygen atoms. Ionized by energetic starlight, the atoms emit their characteristic light as electrons are recaptured and the atoms transition to a lower energy state. As a result, in this image the LMC seems covered with its own clouds of ionized gas surrounding its massive, young stars. Sculpted by the strong stellar winds and ultraviolet radiation, the glowing clouds, dominated by emission from hydrogen, are known as H II (ionized hydrogen) regions. Itself composed of many overlapping H II regions, the Tarantula Nebula is the large star forming region at the left. The largest satellite of our Milky Way Galaxy, the LMC is about 15,000 light-years across and lies a mere 160,000 light-years away toward the constellation Dorado.

Saturn and the Da Vinci Glow

On February 2nd early morning risers saw Saturn near an old Moon low on the eastern horizon. On that date bright planet, sunlit crescent, and faint lunar night side were captured in this predawn skyscape from Bursa, Turkey. Of course the Moon's ashen glow is earthshine, earthlight reflected from the Moon's night side. A description of earthshine, in terms of sunlight reflected by Earth's oceans illuminating the Moon's dark surface, was written over 500 years ago by Leonardo da Vinci. On May 2nd an old Moon also rose in the predawn twilight. On that date its ashen glow shared the sky with Venus, the brilliant morning star. May 2nd also marked the 500th anniversary of Leonardo's death in 1519.

Saturn, Titan, Rings, and Haze

This is not a solar eclipse. Pictured here is a busy vista of moons and rings taken at Saturn. The large circular object in the center of the image is Titan, the largest moon of Saturn and one of the most intriguing objects in the entire Solar System. The dark spot in the center is the main solid part of the moon. The bright surrounding ring is atmospheric haze above Titan, gas that is scattering sunlight to a camera operating onboard the robotic Cassini spacecraft. Cutting horizontally across the image are the rings of Saturn, seen nearly edge on. At the lower right of Titan is Enceladus, a small moon of Saturn. Since the image was taken pointing nearly at the Sun, the surfaces of Titan and Enceladus appear in silhouette, and the rings of Saturn appear similar to a photographic negative. Now if you look really really closely at Enceladus, you can see a hint of icy jets shooting out toward the bottom of the image. It is these jets that inspired future proposals to land on Enceladus, burrow into the ice, and search for signs of extraterrestrial life.

Virtual Flyby of the Whirlpool Galaxy

What would it look like to fly over a spiral galaxy? To help visualize this, astronomers and animators at the Space Telescope Science Institute computed a virtual flyby of the Whirlpool Galaxy (M51) using data and images from the Hubble Space Telescope. At only 25 million light years distant and fully 50 thousand light years across, the Whirlpool is one of the brightest and most picturesque galaxies on the sky. Visible during the virtual flyby are spiral arms dominated by young blue stars, older lighter-colored stars, dark lanes of dust, and bright red emission nebulae. Many galaxies far in the distance can be seen right through M51. The visualization should be considered a time-lapse, because otherwise the speed of the virtual camera would need to be very near the speed of light.

The Great Nebula in Carina

What's happening in the center of the Carina Nebula? Stars are forming, dying, and leaving an impressive tapestry of dark dusty filaments. The entire Carina Nebula, cataloged as NGC 3372, spans over 300 light years and lies about 8,500 light-years away in the constellation of Carina. The nebula is composed predominantly of hydrogen gas, which emits the pervasive red glow seen in this highly detailed featured image. The blue glow in the center is created by a trace amount of glowing oxygen. Young and massive stars located in the nebula's center expel dust when they explode in supernovae. Eta Carinae, the most energetic star in the nebula's center, was one of the brightest stars in the sky in the 1830s, but then faded dramatically.

Jupiter Marble from Juno

What does Jupiter look like up close? Most images of Jupiter are taken from far away, either from Earth or from a great enough distance that nearly half the planet is visible. This shot, though, was composed from images taken relatively close in, where less than half of the planet was visible. From here, Jupiter still appears spherical but perspective distortion now makes it look more like a marble. Visible on Jupiter's cloud tops are a prominent dark horizontal belt containing a white oval cloud, and a white zone cloud, both of which circle the planet. The Great Red Spot looms on the upper right. The featured image was taken by the robotic Juno spacecraft in February during its 17th close pass of our Solar System's largest planet. Juno's mission, now extended into 2021, is to study Jupiter in new ways. Juno's data has already enabled discoveries that include Jupiter's magnetic field being surprisingly lumpy, and that some of Jupiter's cloud systems run about 3,000 kilometers into the planet.

Messier 5

"Beautiful Nebula discovered between the Balance [Libra] & the Serpent [Serpens] ..." begins the description of the 5th entry in 18th century astronomer Charles Messier's famous catalog of nebulae and star clusters. Though it appeared to Messier to be fuzzy and round and without stars, Messier 5 (M5) is now known to be a globular star cluster, 100,000 stars or more, bound by gravity and packed into a region around 165 light-years in diameter. It lies some 25,000 light-years away. Roaming the halo of our galaxy, globular star clusters are ancient members of the Milky Way. M5 is one of the oldest globulars, its stars estimated to be nearly 13 billion years old. The beautiful star cluster is a popular target for earthbound telescopes. Even close to its dense core, the cluster's red and blue giant stars, and rejuvenated blue stragglers stand out with yellowish and blue hues in this sharp color image.

Halley Dust and Milky Way

Grains of cosmic dust streaked through the mostly moonless night skies of May 7. Swept up as planet Earth plowed through the debris streams left behind by periodic Comet Halley, the annual meteor shower is known as the Eta Aquarids. Though it was made about a day after the shower's predicted maximum, this composite image still captures 20 meteors in exposures taken over a 2 hour period, registered on a background exposure of the sky. The meteor trails point back to the shower radiant near eponymous faint star Eta Aquarii close to the horizon, seen from 100 kilometers south of Sydney Australia. Known for speed, Eta Aquarid meteors move fast, entering the atmosphere at about 66 kilometers per second. Brilliant Jupiter shines near the central bulge of the Milky Way high above the horizon. The Southern Cross is just tucked in to the upper right corner of the frame.

Milky Way, Launch, and Landing

The Milky Way doesn't look quite this colorful and bright to the eye, but a rocket launch does. So a separate deep exposure with a sensitive digital camera was used in this composite skyscape to bring out our galaxy's central crowded starfields and cosmic dust clouds. In the scene from Merritt Island National Wildlife Refuge, a nine minute long exposure begun about 20 minutes after the Miky Way image recorded a rocket launch and landing. The Falcon 9 rocket, named for the Millennium Falcon of Star Wars fame, appropriately launched a Dragon resupply ship to the International Space Station in the early morning hours of May the 4th. The plume and flare at the peak of the launch arc mark the rocket's first stage boost back burn. Two shorter diagonal streaks are the rocket engines bringing the Falcon 9 stage back to an offshore landing on autonomous drone ship Of course I Still Love You.

Ash and Lightning above an Icelandic Volcano

Why did a picturesque volcanic eruption in Iceland create so much ash? Although the large ash plume was not unparalleled in its abundance, its location was particularly noticeable because it drifted across such well-populated areas. The Eyjafjallajökull volcano in southern Iceland began erupting on 2010 March 20, with a second eruption starting under the center of a small glacier on 2010 April 14. Neither eruption was unusually powerful. The second eruption, however, melted a large amount of glacial ice which then cooled and fragmented lava into gritty glass particles that were carried up with the rising volcanic plume. Pictured here during the second eruption, lightning bolts illuminate ash pouring out of the Eyjafjallajökull volcano. Follow APOD on: Instagram, Facebook, Reddit, or Twitter

Rho Ophiuchi Wide Field

The colorful clouds surrounding the star system Rho Ophiuchi compose one of the closest star forming regions. Rho Ophiuchi itself is a binary star system visible in the blue reflection nebula just to the left of the image center. The star system, located only 400 light years away, is distinguished by its multi-colored surroundings, which include a red emission nebula and numerous light and dark brown dust lanes. Near the lower left of the Rho Ophiuchi molecular cloud system is the yellow star Antares, while a distant but coincidently-superposed globular cluster of stars, M4, is visible just to the right of Antares. Near the image top lies IC 4592, the Blue Horsehead nebula. The blue glow that surrounds the Blue Horsehead's eye -- and other stars around the image -- is a reflection nebula composed of fine dust. On the featured image right is a geometrically angled reflection nebula cataloged as Sharpless 1. Here, the bright star near the dust vortex creates the light of surrounding reflection nebula. Although most of these features are visible through a small telescope pointed toward the constellations of Ophiuchus, Scorpius, and Sagittarius, the only way to see the intricate details of the dust swirls, as featured above, is to use a long exposure camera.

Young Star Cluster Trumpler 14 from Hubble

Why does star cluster Trumpler 14 have so many bright stars? Because it is so young. Many cluster stars have formed only in the past 5 million years and are so hot they emit detectable X-rays. In older star clusters, most stars this young have already died -- typically exploding in a supernova -- leaving behind stars that are fainter and redder. Trumpler 14 spans about 40 light years and lies about 9,000 light years away on the edge of the famous Carina Nebula. A discerning eye can spot two unusual objects in this detailed 2006 image of Trumpler 14 by the Hubble Space Telescope. First, a dark cloud just left of center may be a planetary system trying to form before being destroyed by the energetic winds of Trumpler 14's massive stars. Second is the arc at the bottom left, which one hypothesis holds is the supersonic shock wave of a fast star ejected 100,000 years ago from a completely different star cluster.

Anemic Spiral NGC 4921 from Hubble

How far away is spiral galaxy NGC 4921? It's surpringly important to know. Although presently estimated to be about 300 million light years distant, a more precise determination could be coupled with its known recession speed to help humanity better calibrate the expansion rate of the entire visible universe. Toward this goal, several images were taken by the Hubble Space Telescope in order to help identify key stellar distance markers known as Cepheid variable stars. Since NGC 4921 is a member of the Coma Cluster of Galaxies, refining its distance would also allow a better distance determination to one of the largest nearby clusters in the local universe. The magnificent spiral NGC 4921 has been informally dubbed anemic because of its low rate of star formation and low surface brightness. Visible in the featured image are, from the center, a bright nucleus, a bright central bar, a prominent ring of dark dust, blue clusters of recently formed stars, several smaller companion galaxies, unrelated galaxies in the far distant universe, and unrelated stars in our Milky Way Galaxy. APOD in other languages: Arabic, Catalan, Chinese (Beijing), Chinese (Taiwan), Croatian, Czech, Dutch, German, French, French, Hebrew, Indonesian, Japanese, Korean, Montenegrin, Polish, Russian, Serbian, Slovenian, Spanish and Ukrainian

Dark Skies: Turn on the Night

Have you ever experienced a really dark night sky? One common and amazing feature is the glowing band of our Milky Way galaxy stretching from horizon to horizon. If you live in or near a big city, though, you might not know this because city lights reflecting off the Earth's atmosphere could only allow you to see the Moon and a few stars. Today, however, being UNESCO's International Day of Light, the International Astronomical Union is asking people to Turn on the Night by trying to better understand, and in the future better reduce, light pollution. You can practice even now by going to the main APOD website at NASA and hovering your cursor over the Before image. The After picture that comes up is a panorama of four exposures taken with the same camera and from the same location, showing what happened recently in China when people in Kaihua County decided to turn down many of their lights. Visible in the Before picture are the stars Sirius (left of center) and Betelgeuse, while visible in the After picture are thousands of stars with the arching band of our Milky Way Galaxy. Humanity has lived for millennia under a dark night sky, and connecting to it has importance for both natural and cultural heritage.

RS Puppis

Pulsating RS Puppis, the brightest star in the image center, is some ten times more massive than our Sun and on average 15,000 times more luminous. In fact, RS Pup is a Cepheid variable star, a class of stars whose brightness is used to estimate distances to nearby galaxies as one of the first steps in establishing the cosmic distance scale. As RS Pup pulsates over a period of about 40 days, its regular changes in brightness are also seen along its surrounding nebula delayed in time, effectively a light echo. Using measurements of the time delay and angular size of the nebula, the known speed of light allows astronomers to geometrically determine the distance to RS Pup to be 6,500 light-years, with a remarkably small error of plus or minus 90 light-years. An impressive achievement for stellar astronomy, the echo-measured distance also more accurately establishes the true brightness of RS Pup, and by extension other Cepheid stars, improving the knowledge of distances to galaxies beyond the Milky Way.

Atlas, Daphnis, and Pan

Atlas, Daphnis, and Pan are small, inner, ring moons of Saturn. They are shown at the same scale in this montage of images by the Cassini spacecraft that made its grand final orbit of the ringed planet in September 2017. In fact, Daphnis was discovered in Cassini images from 2005. Atlas and Pan were first sighted in images from the Voyager 1 and 2 spacecraft. Flying saucer-shaped Atlas orbits near the outer edge of Saturn's bright A Ring while Daphnis orbits inside the A Ring's narrow Keeler Gap and Pan within the A Ring's larger Encke Gap. The curious equatorial ridges of the small ring moons could be built up by the accumulation of ring material over time. Even diminutive Daphnis makes waves in the ring material as it glides along the edge of the Keeler Gap.

A Circumhorizontal Arc Over Ohio

Why would clouds appear to be different colors? The reason here is that ice crystals in distant cirrus clouds are acting like little floating prisms. Sometimes known as a fire rainbow for its flame-like appearance, a circumhorizon arc lies parallel to the horizon. For a circumhorizontal arc to be visible, the Sun must be at least 58 degrees high in a sky where cirrus clouds are present. Furthermore, the numerous, flat, hexagonal ice-crystals that compose the cirrus cloud must be aligned horizontally to properly refract sunlight in a collectively similar manner. Therefore, circumhorizontal arcs are quite unusual to see. This circumhorizon display was photographed through a polarized lens above Dublin, Ohio in 2009.

Planets of the Solar System: Tilts and Spins

How does your favorite planet spin? Does it spin rapidly around a nearly vertical axis, or horizontally, or backwards? The featured video animates NASA images of all eight planets in our Solar System to show them spinning side-by-side for an easy comparison. In the time-lapse video, a day on Earth -- one Earth rotation -- takes just a few seconds. Jupiter rotates the fastest, while Venus spins not only the slowest (can you see it?), but backwards. The inner rocky planets, across the top, most certainly underwent dramatic spin-altering collisions during the early days of the Solar System. The reasons why planets spin and tilt as they do remains a topic of research with much insight gained from modern computer modeling and the recent discovery and analysis of hundreds of exoplanets: planets orbiting other stars.

Deep Field: Nebulae of Sagittarius

These three bright nebulae are often featured on telescopic tours of the constellation Sagittarius and the crowded starfields of the central Milky Way. In fact, 18th century cosmic tourist Charles Messier cataloged two of them; M8, the large nebula just left of center, and colorful M20 on the top left. The third emission region includes NGC 6559 and can be found to the right of M8. All three are stellar nurseries about five thousand light-years or so distant. Over a hundred light-years across, the expansive M8 is also known as the Lagoon Nebula. M20's popular moniker is the Trifid. Glowing hydrogen gas creates the dominant red color of the emission nebulae. In striking contrast, blue hues in the Trifid are due to dust reflected starlight. Recently formed bright blue stars are visible nearby. The colorful composite skyscape was recorded in 2018 in Teide National Park in the Canary Islands, Spain.

Primordial Contact Binary 2014 MU69

Primordial contact binary 2014 MU69, also known as Ultima Thule, really is very red. In fact, it's the reddest outer solar system object ever visited by a spacecraft from Earth. Its reddish hue is believed to be due to organic materials on its surface. Ruddy color and tantalizing surface details seen in this composite image are based on data from the New Horizons spacecraft recorded during the January 1 flyby of the farthest world yet explored. Embedded in the smaller lobe Thule (top), the 8 kilometer wide feature nick named Maryland crater is the largest depression known on the surface of Ultima Thule. Transmission of data collected from the flyby continues, and will go on until the late summer 2020 as New Horizons speeds deeper into the dim and distant Kuiper Belt.

Moons Near Jupiter

On May 20, a nearly Full Moon and Jupiter shared this telephoto field of view. Captured when a passing cloud bank dimmed the moonlight, the single exposure reveals the familiar face of our fair planet's own large natural satellite, along with bright Jupiter (lower right) and some of its Galilean moons. Lined up left to right the tiny pinpricks of light near Jupiter are Ganymede, Europa, [Jupiter] and Callisto. (That's not just dust on your screen ...) Closer and brighter, our own natural satellite appears to loom large. But Ganymede, and Callisto are physically larger than Earth's Moon, while water world Europa is only slightly smaller. In fact, of the Solar System's six largest planetary satellites, Saturn's moon Titan is missing from the scene and a fourth Galilean moon, Io, is hidden by our ruling gas giant.

Boulders on Bennu

An abundance of boulders litters the surface asteroid 101955 Bennu in this dramatic close-up from the OSIRIS-REx spacecraft. Taken on March 28 from a distance of just 3.4 kilometers (2.1 miles) the field of view is about 50 meters across while the light colored boulder at top right is 4.8 meters tall. Likely a loose conglomerate rubble pile asteroid, Bennu itself spans less than 500 meters. That's about the height of the Empire State Building. Mapping the near Earth asteroid since the spacecraft's arrival in December of 2018, the OSIRIS-REx mission plans a TAG (Touch-and-Go) maneuver for July 2020 to sample Bennu's rugged surface, returning the sample to planet Earth in September 2023. Citizen scientists have been invited to help choose the sample collection site.

Planet of the Tajinastes

What bizarre planet are these alien creatures from? It's only planet Earth, of course. The planet's home galaxy the Milky Way stretches across a dark sky in the panoramic, fisheye all-sky projection composed with a wide lens. But the imposing forms gazing skyward probably look strange to many denizens of Earth. Found on the Canary Island of Tenerife in the Teide National Park, they are red tajinastes, flowering plants that grow to a height of up to 3 meters. Among the rocks of the volcanic terrain, tajinastes bloom in spring and early summer and then die after a week or so as their seeds mature. A species known as Echium wildpretii, the terrestrial life forms were individually lit by flashlight during the wide-angle exposures.

A Solar Prominence Eruption from SDO

One of the most spectacular solar sights is an erupting prominence. In 2011, NASA's Sun-orbiting Solar Dynamic Observatory spacecraft imaged an impressively large prominence erupting from the surface. The dramatic explosion was captured in ultraviolet light in the featured time lapse video covering 90 minutes, where a new frame was taken every 24 seconds. The scale of the prominence is huge -- the entire Earth would easily fit under the flowing curtain of hot gas. A solar prominence is channeled and sometimes held above the Sun's surface by the Sun's magnetic field. A quiescent prominence typically lasts about a month, and may erupt in a Coronal Mass Ejection (CME) expelling hot gas into the Solar System. The energy mechanism that creates a solar prominence is still a topic of research. After our Sun passes the current Solar Minimum, solar activity like eruptive prominences are expected to become more common over the next few years.

A Volcano of Fire under a Milky Way of Stars

Sometimes it's hard to decide which is more impressive -- the land or the sky. On the land of the featured image, for example, the Volcano of Fire (Volcán de Fuego) is seen erupting topped by red-hot, wind-blown ash and with streams of glowing lava running down its side. Lights from neighboring towns are seen through a thin haze below. In the sky, though, the central plane of our Milky Way Galaxy runs diagonally from the upper left, with a fleeting meteor just below, and the trail of a satellite to the upper right. The planet Jupiter also appears toward the upper left, with the bright star Antares just to its right. Much of the land and the sky were captured together in a single, well-timed, 25-second exposure taken in mid-April from the side of Fuego's sister volcano Acatenango in Guatemala. The image of the meteor, though, was captured in a similar frame taken about 30 minutes earlier -- when the volanic eruption was not as photogenic -- and added later digitally. Follow APOD on: Instagram, Facebook, Reddit, or Twitter

Stars, Dust, and Gas near NGC 3572

Star formation can be colorful. This chromatic cosmic portrait features glowing gas and dark dust near some recently formed stars of NGC 3572, a little-studied star cluster near the Carina Nebula. Stars from NGC 3572 are visible near the bottom of the image, while the expansive gas cloud above is likely what remains of their formation nebula. The image's striking hues were created by featuring specific colors emitted by hydrogen, oxygen, and sulfur, and blending them with images recorded through broadband filters in red, green, and blue. This nebula near NGC 3572 spans about 100 light years and lies about 9,000 light years away toward the southern constellation of the Ship's Keel (Carina). Within a few million years the pictured gas will likely disperse, while gravitational encounters will likely disperse the cluster stars over about a billion years. Astrophysicists: Browse 1,900+ codes in the Astrophysics Source Code Library

M95: Spiral Galaxy with an Inner Ring

Why do some spiral galaxies have a ring around the center? First and foremost, M95 is one of the closer examples of a big and beautiful barred spiral galaxy. Visible in the featured combination of images from Hubble and several ground based telescopes are sprawling spiral arms delineated by open clusters of bright blue stars, lanes of dark dust, the diffuse glow of billions of faint stars, and a short bar across the galaxy center. What intrigues many astronomers, however, is the circumnuclear ring around the galaxy center visible just outside the central bar. Although the long term stability of this ring remains a topic of research, observations indicate its present brightness is at least enhanced by transient bursts of star formation. M95, also known as NGC 3351, spans about 50,000 light-years, lies about 30 million light years away, and can be seen with a small telescope toward the constellation of the Lion (Leo). Almost Hyperspace: Random APOD Generator

Sunrise at Copernicus Crater

A prominent impact site anchored in the lunar Oceanus Procellarum, Copernicus crater is at the center of this telescopic portrait in light and shadow. Caught in stacked and sharpened video frames recorded on April 14 at 3:30am UTC, the lunar terminator, or boundary between night and day, cuts across the middle of the 93 kilometer diameter crater. Sunlight is just beginning to strike its tall western walls but doesn't yet shine on lower terrain nearby, briefly extending the crater's outline into the lunar nightside. At that moment standing at Copernicus crater you could watch the sunrise, an event that happens at Copernicus every 29.5 days. Of course that corresponds to a lunar month or a lunation, the time between consecutive Full Moons, as seen from planet Earth.

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