NASA's Astronomy Picture of the Day
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Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
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2016 February 10

Galaxies in the River
Image Credit &
Copyright: CEDIC Team - Processing: Markus Blauensteiner

Large galaxies grow by eating small ones. Even our own galaxy practices galactic cannibalism, absorbing small galaxies that get too close and are captured by the Milky Way's gravity. In fact, the practice is common in the universe and illustrated by this striking pair of interacting galaxies from the banks of the southern constellation Eridanus, The River. Located over 50 million light years away, the large, distorted spiral NGC 1532 is seen locked in a gravitational struggle with dwarf galaxy NGC 1531 (right of center), a struggle the smaller galaxy will eventually lose. Seen edge-on, spiral NGC 1532 spans about 100,000 light-years. Nicely detailed in this sharp image, the NGC 1532/1531 pair is thought to be similar to the well-studied system of face-on spiral and small companion known as M51.
2016 February 11

LIGO Detects Gravitational Waves from Merging Black Holes
Illustration Credit:
LIGO, NSF, Aurore Simonnet (Sonoma State U.)

Gravitational radiation has been directly detected. The first-ever detection was made by both facilities of the Laser Interferometer Gravitational-Wave Observatory (LIGO) in Washington and Louisiana simultaneously last September. After numerous consistency checks, the resulting 5-sigma discovery was published today. The measured gravitational waves match those expected from two large black holes merging after a death spiral in a distant galaxy, with the resulting new black hole momentarily vibrating in a rapid ringdown. A phenomenon predicted by Einstein, the historic discovery confirms a cornerstone of humanity's understanding of gravity and basic physics. It is also the most direct detection of black holes ever. The featured illustration depicts the two merging black holes with the signal strength of the two detectors over 0.3 seconds superimposed across the bottom. Expected future detections by Advanced LIGO and other gravitational wave detectors may not only confirm the spectacular nature of this measurement but hold tremendous promise of giving humanity a new way to see and explore our universe.
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2016 February 12

Two Black Holes Merge
Simulation Credit:
Simulating eXtreme Spacetimes Project

Just press play to watch two black holes merge. Inspired by the first direct detection of gravitational waves by LIGO, this simulation video plays in slow motion but would take about one third of a second if run in real time. Set on a cosmic stage the black holes are posed in front of stars, gas, and dust. Their extreme gravity lenses the light from behind them into Einstein rings as they spiral closer and finally merge into one. The otherwise invisible gravitational waves generated as the massive objects rapidly coalesce cause the visible image to ripple and slosh both inside and outside the Einstein rings even after the black holes have merged. Dubbed GW150914, the gravitational waves detected by LIGO are consistent with the merger of 36 and 29 solar mass black holes at a distance of 1.3 billion light-years. The final, single black hole has 62 times the mass of the Sun, with the remaining 3 solar masses converted into energy in gravitational waves.
2016 February 13

Yutu on a Little Planet
Image Credit:
Chinese Academy of Sciences, Chinese National Space Administration,
Emily Lakdawalla (Planetary Society) - Stitched by: Andrew Bodrov

Tracks lead to a small robot perched near the top of this bright little planet. Of course, the planet is really the Moon. The robot is the desk-sized Yutu rover, leaving its looming Chang'e 3 lander after a mid-December 2013 touch down in the northern Mare Imbrium. The little planet projection is a digitally warped and stitched mosaic of images from the lander's terrain camera covering 360 by 180 degrees. Ultimately traveling over 100 meters, Yutu came to a halt in January 2014. The lander's instruments are still working though, after more than two years on the lunar surface. Meanwhile, an interactive panoramic version of this little planet is available here.
2016 February 14

A Heart Shaped Lenticular Cloud
Image Credit & Copyright:
Michael Kunze

Can a cloud love a mountain? Perhaps not, but on a Valentine's Day like today, one might be prone to seeing heart-shaped symbols where they don't actually exist. A fleeting pareidolia, the featured heart was really a lenticular cloud that appeared one morning last July above Mount Cook National Park in New Zealand. A companion video shows the lenticular cloud was mostly stationary in the sky but shifted and vibrated with surrounding winds. The cloud's red color was caused by the Sun rising off the frame to the right. Lenticular clouds are somewhat rare but can form in air that passes over a mountain. Then, vertical eddies may form where rising air cools past the dew point causing water carried by the air to condense into droplets. Unfortunately, this amazing sight made the fascinated videographer late for breakfast.
2016 February 15

White Rock Fingers on Mars
Image Credit:
THEMIS, Mars Odyssey Team, ASU, JPL, NASA

What caused this unusual light rock formation on Mars? Intrigued by the possibility that they could be salt deposits left over as an ancient lakebed dried-up, detailed studies of these fingers now indicate a more mundane possibility: volcanic ash. Studying the exact color of the formation indicated the possible volcanic origin. The light material appears to have eroded away from surrounding area, indicating a very low-density substance. The stark contrast between the rocks and the surrounding sand is compounded by the unusual darkness of the sand. The featured picture was taken with the Thermal Emission Imaging System on the Mars Odyssey, the longest serving spacecraft currently orbiting Mars. The image spans about 10 kilometers inside a larger crater.
2016 February 16

Star Forming Region S106
Image Credit:
NASA, ESA, Hubble Legacy Archive; Processed & Copyright: Brandon Pimenta

Massive star IRS 4 is beginning to spread its wings. Born only about 100,000 years ago, material streaming out from this newborn star has formed the nebula dubbed Sharpless 2-106 Nebula (S106), featured here. A large disk of dust and gas orbiting Infrared Source 4 (IRS 4), visible in brown near the image center, gives the nebula an hourglass or butterfly shape. S106 gas near IRS 4 acts as an emission nebula as it emits light after being ionized, while dust far from IRS 4 reflects light from the central star and so acts as a reflection nebula. Detailed inspection of a recent infrared image of S106 reveal hundreds of low-mass brown dwarf stars lurking in the nebula's gas. S106 spans about 2 light-years and lies about 2000 light-years away toward the constellation of the Swan (Cygnus).
2016 February 17

Milky Way over the Pinnacles in Australia
Image Credit:
Michael Goh

What strange world is this? Earth. In the foreground of the featured image are the Pinnacles, unusual rock spires in Nambung National Park in Western Australia. Made of ancient sea shells (limestone), how these human-sized picturesque spires formed remains unknown. In the background, just past the end of the central Pinnacle, is a bright crescent Moon. The eerie glow around the Moon is mostly zodiacal light, sunlight reflected by dust grains orbiting between the planets in the Solar System. Arching across the top is the central band of our Milky Way Galaxy. Many famous stars and nebula are also visible in the background night sky. The featured 29-panel panorama was taken and composed last September after detailed planning that involved the Moon, the rock spires, and their corresponding shadows. Even so, the strong zodiacal light was a pleasant surprise.
2016 February 18

Hitomi Launches
Image Credit &
Copyright: F. Scott Porter (NASA, Goddard Space Flight Center)

On February 17 at 5:45pm JST this H-IIA rocket blasted skyward from JAXA's Tanegashima Space Center located off the southern coast of Japan, planet Earth. Onboard was the ASTRO-H X-ray astronomy satellite, now in orbit. Designed to explore the extreme cosmos from black holes to massive galaxy clusters, the satellite observatory is equipped with four cutting-edge X-ray telescopes and instruments sensitive to photon energies from 300 to 600,000 electron volts. By comparison, visible light photon energies are 2 to 3 electron volts. Following a tradition of renaming satellites after their successful launch, ASTRO-H has been newly dubbed "Hitomi", inspired by an ancient legend of dragons. Hitomi means "the pupil of the eye".
2016 February 19

NGC 2403 in Camelopardalis
Image Credit &
Copyright: Eric Coles and Mel Helm

Magnificent island universe NGC 2403 stands within the boundaries of the long-necked constellation Camelopardalis. Some 10 million light-years distant and about 50,000 light-years across, the spiral galaxy also seems to have more than its fair share of giant star forming HII regions, marked by the telltale reddish glow of atomic hydrogen gas. The giant HII regions are energized by clusters of hot, massive stars that explode as bright supernovae at the end of their short and furious lives. A member of the M81 group of galaxies, NGC 2403 closely resembles another galaxy with an abundance of star forming regions that lies within our own local galaxy group, M33 the Triangulum Galaxy. Spiky in appearance, bright stars in this colorful galaxy portrait of NGC 2403 are in the foreground, within our own Milky Way.
2016 February 20

Where Your Shadow Has Company
Poster Illustration Credit:
NASA, JPL, Exoplanet Travel Bureau

Want to take a relaxing interstellar vacation? Consider visiting Kepler-16b, a world in a binary star system. In fact Kepler-16b is the first discovered circumbinary planet. It was detected in a wide 229 day orbit around a close pair of cool, low-mass stars some 200 light-years away. The parent stars eclipse one another in their orbits, observed as a periodic dimming of starlight. But Kepler-16b itself was discovered by following the additional very slight dimming produced during its transits. Like sci-fi planet Tatooine of Star Wars fame, two suns would set over its horizon. Still, Kepler-16b is probably not a Tatooine-like terrestrial desert world. Instead, Kepler-16b is thought to be a cold, uninhabitable planet with about the mass of Saturn and a gaseous surface ... so plan to dress accordingly. Or, choose another Visions of the Future vacation destination.
2016 February 21

M82: Galaxy with a Supergalactic Wind
Image Credit:
NASA, ESA, The Hubble Heritage Team, (STScI/AURA)
Acknowledgement: M. Mountain (STScI), P. Puxley (NSF), J. Gallagher (U. Wisconsin)

What's lighting up the Cigar Galaxy? M82, as this irregular galaxy is also known, was stirred up by a recent pass near large spiral galaxy M81. This doesn't fully explain the source of the red-glowing outwardly expanding gas, however. Evidence indicates that this gas is being driven out by the combined emerging particle winds of many stars, together creating a galactic superwind. The featured photographic mosaic highlights a specific color of red light strongly emitted by ionized hydrogen gas, showing detailed filaments of this gas. The filaments extend for over 10,000 light years. The 12-million light-year distant Cigar Galaxy is the brightest galaxy in the sky in infrared light, and can be seen in visible light with a small telescope towards the constellation of the Great Bear (Ursa Major).
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2016 February 22

Flying Over Pluto's Moon Charon
Video Credit:
NASA, Johns Hopkins U. APL, SwRI, Stuart Robbins

Given some poetic license, there is now scientific evidence that hell has frozen over. To start, Greek mythology holds that Charon is the ferryman of the underworld. Next, recent analysis of data taken by the robotic New Horizons spacecraft that shot past Charon -- the namesake that is the largest moon of Pluto -- in July now indicates that the cause of the huge chasm that runs across the 1200-km moon was that a huge internal sea froze. And since water expands when it freezes, the already hardened outer crust could not contain it and cracked. To better picture the crack, a fanciful journey over some of Charon's has been digitally created from collected images. The featured video starts by showing the Dark Polar Deposit (dubbed Mordor) near Charon's north pole and then flies over the dwarf-planet-wide canyon. Last, the video shows a much-debated protuberance called Moated Mountain. Understanding the history of Pluto and Charon is helping humanity to better understand both the friendliest and more forbidding places in the early Solar System from which Earth formed and life somehow emerged.
2016 February 23

A Supernova through Galaxy Dust
Image Credit:
NASA, ESA, and the Hubble Heritage (STScI/AURA);
Inset Image: Howard Hedlund & Dave Jurasevich, Las Campanas Obs.

Telescopes around the world are tracking a bright supernova that occurred in a nearby dusty galaxy. The powerful stellar explosion was first noted earlier this month. The nearby galaxy is the photogenic Centaurus A, visible with binoculars and known for impressive filaments of light-absorbing dust that cross its center. Cen A is featured here in a high-resolution archival Hubble Space Telescope image, with an inset image featuring the supernova taken from the ground only two days after discovery. Designated SN2016adj, the supernova is highlighted with crosshairs in the inset, appearing just to the left of a bright foreground star in our Milky Way Galaxy. This supernova is currently thought to be of Type IIb, a stellar-core-collapse supernova, and is of high interest because it occurred so nearby and because it is being seen through a known dust filament. Current and future observations of this supernova may give us new clues about the fates of massive stars and how some elements found on our Earth were formed.
2016 February 24

USA's Northeast Megalopolis from Space
Image Credit:
NASA, International Space Station

Can you identify a familiar area in the northeast USA just from nighttime lights? It might be possible because many major cities are visible, including (right to left) New York, Philadelphia, Baltimore, Washington, Richmond and Norfolk -- Boston of the USA's Northeast megalopolis is not pictured. The featured image was taken in 2012 from the International Space Station. In the foreground are two Russian cargo ships with prominent solar panels. This Northeast megalopolis of the USA contains almost 20 percent of the people of the USA but only about 2 percent of the land area. Also known also as the Northeast Corridor and part of the Eastern Seaboard, about 10 percent of the world's largest companies are headquartered here. The near continuity of the lights seem to add credence to the 1960s-era prediction that the entire stretch is evolving into one continuous city.
2016 February 25

Highest, Tallest, and Closest to the Stars
Image Credit &
Copyright: Jeff Dai, O Chul Kwon, Stéphane Guisard (Los Cielos de America), TWAN

Fans of planet Earth probably recognize its highest mountain, the Himalayan Mount Everest, on the left in this 3-panel skyscape of The World at Night. Shrouded in cloud Everest's peak is at 8,848 meters (29,029 feet) elevation above sea level. In the middle panel, stars trail above volcanic Mauna Kea forming part of the island of Hawaii. Festooned with astronomical observatories, its summit lies a mere 4,168 meters above sea level. Still, measured from its base starting below the ocean's surface, Mauna Kea is over 10,000 meters tall, making it Earth's tallest mountain from base to summit. At right, beneath the arc of the Milky Way is the Andean mountain Chimborazo in Ecuador. The highest equatorial mountain, the Chimborazo volcano's peak elevation is 6,268 meters above sea level. But rotating planet Earth is a flattened sphere (oblate spheroid) in shape, its equatorial diameter greater than its diameter measured pole to pole. Sitting nearly on top of Earth's greatest equatorial bulge, Chimborazo's peak is the farthest point on the planet's surface from the center, over 2,000 meters farther from the center of the Earth than Everest's peak. That makes Chimborazo's summit the place on Earth's surface closest to the stars.
2016 February 26

The Tarantula Nebula
Image Credit &
Copyright: Processing - Robert Gendler, Roberto Colombari
Data - Hubble Tarantula Treasury, European Southern Observatory

The Tarantula Nebula is more than a thousand light-years in diameter, a giant star forming region within nearby satellite galaxy the Large Magellanic Cloud, about 180 thousand light-years away. The largest, most violent star forming region known in the whole Local Group of galaxies, the cosmic arachnid sprawls across this spectacular composite view constructed with space- and ground-based image data. Within the Tarantula (NGC 2070), intense radiation, stellar winds and supernova shocks from the central young cluster of massive stars, cataloged as R136, energize the nebular glow and shape the spidery filaments. Around the Tarantula are other star forming regions with young star clusters, filaments, and blown-out bubble-shaped clouds In fact, the frame includes the site of the closest supernova in modern times, SN 1987A, at the lower right. The rich field of view spans about 1 degree or 2 full moons, in the southern constellation Dorado. But were the Tarantula Nebula closer, say 1,500 light-years distant like the local star forming Orion Nebula, it would take up half the sky.
2016 February 27

Northern Pluto
Image Credit:
NASA, Johns Hopkins Univ./APL, Southwest Research Institute

Gaze across the frozen canyons of northern Pluto in this contrast enhanced color scene, imaged last July by the New Horizons spacecraft. Currently known as Lowell Regio, the region has been informally named for Percival Lowell, founder of the Lowell Observatory. Also famous for his speculation that there were canals on Mars, in 1906 Lowell started the search that ultimately led to Pluto's discovery. Pluto's North Pole itself is above and left of center in the the frame. The pale bluish floor of the broad canyon on the left is about 70 kilometers (45 miles) wide, running vertically toward the south. Higher elevations take on a yellowish hue. New Horizon's measurements have determined that in addition to nitrogen ice, methane ice is abundant across northern Pluto's Lowell Regio.
2016 February 28

IC 1848: The Soul Nebula
Image Credit & Copyright:
Roberto Colombari

Stars are forming in the Soul of the Queen of Aethopia. More specifically, a large star forming region called the Soul Nebula can be found in the direction of the constellation Cassiopeia, who Greek mythology credits as the vain wife of a King who long ago ruled lands surrounding the upper Nile river. The Soul Nebula houses several open clusters of stars, a large radio source known as W5, and huge evacuated bubbles formed by the winds of young massive stars. Located about 6,500 light years away, the Soul Nebula spans about 100 light years and is usually imaged next to its celestial neighbor the Heart Nebula (IC 1805). The featured image appears mostly red due to the emission of a specific color of light emitted by excited hydrogen gas.
2016 February 29

Julius Caesar and Leap Days
Image Credit:
Classical Numismatic Group, Inc., Wikimedia

Today, February 29th, is a leap day - a relatively rare occurrence. In 46 BC, Julius Caesar, featured here in a self-decreed minted coin, created a calendar system that added one leap day every four years. Acting on advice by Alexandrian astronomer Sosigenes, Caesar did this to make up for the fact that the Earth's year is slightly more than 365 days. In modern terms, the time it takes for the Earth to circle the Sun is slightly more than the time it takes for the Earth to rotate 365 times (with respect to the Sun -- actually we now know this takes about 365.24219 rotations). So, if calendar years contained 365 days they would drift from the actual year by about 1 day every 4 years. Eventually July (named posthumously for Julius Caesar himself) would occur during the northern hemisphere winter! By adopting a leap year with an extra day every four years, the calendar year would drift much less. This Julian Calendar system was used until the year 1582 when Pope Gregory XIII provided further fine-tuning when he added that leap days should not occur in years ending in "00", unless divisible by 400. This Gregorian Calendar system is the one in common use today.
2016 March 1

NGC 3310: A Starburst Spiral Galaxy
Image Credit & Copyright:
AAO ITSO Office, Gemini Obs./AURA & T. A. Rector (U. Alaska Anchorage)

The party is still going on in spiral galaxy NGC 3310. Roughly 100 million years ago, NGC 3310 likely collided with a smaller galaxy causing the large spiral galaxy to light up with a tremendous burst of star formation. The changing gravity during the collision created density waves that compressed existing clouds of gas and triggered the star-forming party. The featured image from the Gemini North Telescope shows the galaxy in great detail, color-coded so that pink highlights gas while white and blue highlight stars. Some of the star clusters in the galaxy are quite young, indicating that starburst galaxies may remain in star-burst mode for quite some time. NGC 3310 spans about 50,000 light years, lies about 50 million light years away, and is visible with a small telescope towards the constellation of Ursa Major.