Astronomy Picture of the Day

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Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2010 June 25

The Starry Night of Alamut
Image Credit & Copyright: Babak Tafreshi (TWAN) Explanation: A meteor's streak and the arc of the Milky Way hang over the imposing mountain fortress of Alamut in this starry scene. Found in the central Alborz Mountains of Iran, Alamut Castle was built into the rock in the 9th century. The name means Eagle's Nest. Home of the legendary Assassins featured in the adventure movie Prince of Persia, Alamut was also historically a center for libraries and education. For a time, it was the residence of important 13th century Persian scholar and astronomer Nasir al-Din al-Tusi. To identify the stars in a night sky Tusi certainly pondered, just slide your cursor over the image. Highlights include bright white stars Deneb (in Cygnus), Vega, and Altair, nebulae near the Galactic Center, and the dark obscuring dust clouds of the Milky Way also known as the Great Rift. Lights at the lower right are from small villages and the capital Tehran, over 100 kilometers away to the southwest.


 

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Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2010 June 26

Young Star Cluster Westerlund 2
Credit: X-ray; Y.Nazé, G.Rauw, J.Manfroid (Université de Liège), CXC, NASA
Infrared; E.Churchwell (University of Wisconsin), JPL, Caltech, NASA Explanation: Dusty stellar nursery RCW 49 surrounds young star cluster Westerlund 2 in this remarkable composite skyscape from beyond the visible spectrum of light. Infrared data from the Spitzer Space Telescope is shown in black and white, complementing the Chandra X-ray image data (in false color) of the hot energetic stars within the cluster's central region. Looking toward the grand southern constellation Centaurus, both views reveal stars and structures hidden from optical telescopes by obscuring dust. Westerlund 2 itself is a mere 2 million years old or less, and contains some of our galaxy's most luminous, massive and therefore short-lived stars. The infrared signatures of proto-planetary disks have also been identified in the intense star forming region. At the cluster's estimated distance of 20,000 light-years, the square marking the Chandra field of view would be about 50 light-years on a side.

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2010 June 27

All the Colors of the Sun
Credit & Copyright: Nigel Sharp (NSF), FTS, NSO, KPNO, AURA, NSF Explanation: It is still not known why the Sun's light is missing some colors. Shown above are all the visible colors of the Sun, produced by passing the Sun's light through a prism-like device. The above spectrum was created at the McMath-Pierce Solar Observatory and shows, first off, that although our white-appearing Sun emits light of nearly every color, it does indeed appear brightest in yellow-green light. The dark patches in the above spectrum arise from gas at or above the Sun's surface absorbing sunlight emitted below. Since different types of gas absorb different colors of light, it is possible to determine what gasses compose the Sun. Helium, for example, was first discovered in 1870 on a solar spectrum and only later found here on Earth. Today, the majority of spectral absorption lines have been identified - but not all.


 

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2010 June 28

A Partial Lunar Eclipse
Credit & Copyright: Brad Riza Explanation: What's happened to the Moon? This past weekend, once again, part of the Moon moved through the Earth's shadow. This happens about once or twice a year, on the average, but not each month since the Moon's orbit around the Earth is slightly tilted. Pictured above, the face of a full moon is partly blocked by Earth's clouds, and partly darkened on the upper right by Earth's umbral shadow. Clouds permitting, the partial lunar eclipse was visible from the half of the Earth facing the Moon at the time of the eclipse, which included much of Earth's Pacific Rim. On July 11, a total eclipse of the Sun will be visible in a thin swath of Earth crossing the southern Pacific Ocean.


 

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Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2010 June 29

Trees, Sky, Galactic Eye
Credit & Copyright: Luc Perrot Explanation: Is beauty in the eye of this beholder? Earlier this month, over Réunion Island in the Indian Ocean, a playful photographer with an eye for the sky took eight images and composed the above intriguing picture. The full fisheye frame shows everything above the horizon, including a lamp-illuminated landscape around the edges, and the zenith of the sky directly overhead. The image, however, may be more than beautiful -- it may also be a scavenger hunt. Can you find the photographer's tent, the slope of a volcano (active Piton de la Fournaise), a picturesque shoreline, and the lights of the nearby town (Saint Philippe)? One remarkable feature of the above image is that its center contains the very center of our Milky Way Galaxy.


 

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2010 June 30

Fast Gas Bullet from Cosmic Blast N49
Credit: X-ray: NASA/CXC/Penn State/S. Park et al.; Optical: NASA/STScI/UIUC/Y. H. Chu & R. Williams et al. Explanation: What is that strange blue blob on the far right? No one is sure, but it might be a speeding remnant of a powerful supernova that was unexpectedly lopsided. Scattered debris from supernova explosion N49 lights up the sky in this gorgeous composited image based on data from the Chandra and Hubble Space Telescopes. Glowing visible filaments, shown in yellow, and X-ray hot gas, shown in blue, span about 30 light-years in our neighboring galaxy, the Large Magellanic Cloud. Light from the original exploding star reached Earth thousands of years ago, but N49 also marks the location of another energetic outburst -- an extremely intense blast of gamma-rays detected by satellites about 30 years ago on 1979 March 5. The source of the March 5th Event is now attributed to a magnetar - a highly magnetized, spinning neutron star also born in the ancient stellar explosion which created supernova remnant N49. The magnetar, visible near the top of the image, hurtles through the supernova debris cloud at over 70 thousand kilometers per hour. The blue blob on the far right, however, might have been expelled asymmetrically just as a massive star was exploding. If so, it now appears to be moving over 7 million kilometers per hour.





 

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2010 July 1

Above Aurora Australis
Credit: ISS Expedition 23 Crew, ISAL, NASA Explanation: On May 29, looking southward from a vantage point about 350 kilometers above the southern Indian Ocean, astronauts onboard the International Space Station watched this enormous, green ribbon shimmering below. Known as aurora australis or southern lights, the shifting, luminous bands are commonly seen at high northern latitudes as well, there known as the aurora borealis or northern lights. North or south their cause is the same though, as energetic charged particles from the magnetosphere pile into the atmosphere near the Earth's poles. To produce the characteristic greenish glow, the energetic particles excite oxygen atoms at altitudes of 100 kilometers or more. Aurora on May 29 were likely triggered by the interaction of the magnetosphere with a coronal mass ejection erupting from the Sun on May 24.

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2010 July 2

Galaxies on a String
Image Credit & Copyright: Adam Block, Mt. Lemmon SkyCenter, U. Arizona Explanation: Galaxies NGC 5216 (top) and NGC 5218 really do look like they are connected by a string. Of course, that string is a cosmic trail of gas, dust, and stars about 22,000 light-years long. Also known as Keenan's system (for its discoverer) and Arp 104, the interacting galaxy pair is some 17 million light-years away in the constellation Ursa Major. The debris trail that joins them, along with NGC 5218's comma-shaped extension and the distorted arms of NGC 5216, are a consequence of mutual gravitational tides. The tides disrupt the galaxies as they repeatedly swing close to one another. Drawn out over billions of years, the encounters will likely result in their merger into a single galaxy of stars. Such spectacular galactic mergers are now understood to be a normal part of the evolution of galaxies, including our own Milky Way.


 

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2010 July 3

A Giant Planet for Beta Pic
Credit: A.-M. Lagrange, D. Ehrenreich (LAOG), et al., ESO Explanation: A mere 50 light-years away, young star Beta Pictoris became one of the most important stars in the sky in the early 1980s. Satellite and ground-based telescopic observations revealed the presence of a surrounding outer, dusty, debris disk and an inner clear zone about the size of our solar system -- strong evidence for the formation of planets. Infrared observations from European Southern Observatory telescopes subsequently detected a source in the clear zone, now confirmed as a giant planet orbiting Beta Pic. The confirmation comes as the planet is detected at two different positions in its orbit. Designated Beta Pictoris b, the giant planet must have formed rapidly as Beta Pic itself is only 8 to 20 million years old. With an orbital period estimated between 17 and 44 years, Beta Pictoris b could lie near the orbit of Saturn if found in our solar system, making it the closest planet to its parent star directly imaged ... so far.


 

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2010 July 4

Companion of a Young, Sun-like Star Confirmed
Credit: Gemini Observatory, D. Lafreniere, R. Jayawardhana, M. van Kerkwijk (Univ. Toronto) Explanation: The first direct image of an extrasolar planet orbiting a star similar to our Sun has been confirmed. Located just 500 light-years away toward the constellation Scorpius, the parent star, cataloged as 1RXS J160929.1-210524, is only slightly less massive and a little cooler than the Sun. The star is, however, much younger, a few million years old compared to the middle-aged Sun's 5 billion years. This sharp infrared image shows the young star's planetary companion positioned above and left of center. The planet is estimated to have a mass about 8 times the mass of Jupiter, and orbit a whopping 330 times the Earth-Sun distance from its parent star. The young planetary companion is still hot and relatively bright in infrared light, likely due to the heat generated during its formation by gravitational contraction. In fact, such newborn planets are easier to detect before they age and cool and become much more faint. The discovery image, shown above, was taken in 2008 but confirmed only recently by noting that the planet stayed with its parent star as background stars slightly shifted over time.


 

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2010 July 5

The Milky Way Over Pulpit Rock
Credit & Copyright: Alex Cherney (Terrastro) Explanation: Can a picture of the sky be relaxing? A candidate for such a picture might be the above image taken only last month from Cape Schank, Victoria, Australia. The frame is highlighted by a quiet lagoon, soft ground fog, two galaxies, and tens of thousands of stars. The rock cropping on the left may appear from this angle like a human head, but the more famous rock structure is on the far right and known as Pulpit Rock. Across the top of the image runs a distant stream of bright stars and dark dust that is part of the disk of our spiral Milky Way Galaxy. On the right, just above Pulpit Rock, is the Milky Way's small neighboring galaxy the Small Magellanic Cloud (SMC). The bright white object just to the left of the SMC is a globular cluster of stars in the Milky Way known as 47 Tucana.

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2010 July 6

HCG 87: A Small Group of Galaxies
Credit: Sally Hunsberger (Lowell Obs.), Jane Charlton (Penn State) et al.;
Data: Hubble Legacy Archive; Processing: Robert Gendler Explanation: Sometimes galaxies form groups. For example, our own Milky Way Galaxy is part of the Local Group of Galaxies. Small, compact groups, like Hickson Compact Group 87 (HCG 87) shown above, are interesting partly because they slowly self-destruct. Indeed, the galaxies of HCG 87 are gravitationally stretching each other during their 100-million year orbits around a common center. The pulling creates colliding gas that causes bright bursts of star formation and feeds matter into their active galaxy centers. HCG 87 is composed of a large edge-on spiral galaxy visible on the lower left, an elliptical galaxy visible on the lower right, and a spiral galaxy visible near the top. The small spiral near the center might be far in the distance. Several stars from our Galaxy are also visible in the foreground. The above picture was taken in 1999 July by the Hubble Space Telescope's Wide Field Planetary Camera 2. Studying groups like HCG 87 allows insight into how all galaxies form and evolve.


 

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2010 July 7

Concept Plane: Supersonic Green Machine
Illustration Credit: NASA, Lockheed Martin Co. Explanation: What will passenger airplanes be like in the future? To help brain storm desirable and workable attributes, NASA sponsors design competitions. Shown here is an artist's depiction of a concept plane that has been recently suggested. This futuristic plane would be expected to achieve supersonic speeds, possibly surpassing the speeds of the supersonic transport planes that ran commercially in the late twentieth century. In terms of noise reduction, the future aircraft has been drawn featuring an inverted V wing stretched over its engines. The structure is intended to reduce the sound from annoying sonic booms. Additionally, future airplanes would aim to have relatively little impact on our environment, including green limits on pollution and fuel consumption. Aircraft utilizing similar design concepts might well become operational by the 2030s.


 

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2010 July 8

Dim World, Dark Nebula
Credit & Copyright: Ray Gralak Explanation: Dim, distant, dwarf planet Pluto can be hard to spot, especially in recent months as it wanders through the crowded starfields of Sagittarius and the central Milky Way. But fortunately for backyard Pluto hunters, it crossed in front of a dark nebula in early July. The diminutive world is marked with two short lines near the center of this skyscape recorded from New Mexico Skies on July 5. Pluto stands out only because obscuring dark nebula Barnard 92 (B92) blocks the background of the Milky Way's congeries of faint, innumerable stars. Another of astronomer E. E. Barnard's cataloged dark markings on the sky, B93, is easy to pick out just left of B92. Prominent at the lower left is open star cluster NGC 6603. In fact, Pluto, dark nebulae, and star cluster all lie within a portion of M24, also known as the Sagittarius Star Cloud, filling most of the frame.


 

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2010 July 9

Microwave Milky Way
Credit: ESA, Planck HFI & LFI Consortia Explanation: Seen from our edge-on perspective, the Milky Way Galaxy sprawls across the middle of this false-color, all sky view. The expansive microwave map is based on 1 year's worth of data from instruments onboard the sky-surveying Planck spacecraft. Remarkably, the bright stripe of gas and dust clouds along the galactic plane and the galaxy's enormous arcing structures seen at microwave energies are hundreds or thousands of light-years away, while the mottled regions at the top and bottom represent the Cosmic Microwave Background (CMB) radiation, some 13.7 billion light-years distant. Left over from the Big Bang, fluctuations in the CMB reflect the origins of structure in the evolving universe. Analyzing the microwave data, Planck scientists plan to separate the contributions of the Milky Way and CMB radiation. The work will ferret out the characteristics of the CMB across the entire sky and glean information about the make up of our Milky Way Galaxy.


 

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2010 July 10

Ecliptic New Zealand
Image Credit & Copyright: Tunç Tezel (TWAN) Explanation: Four bright celestial beacons and a faint triangle of light follow the plane of the ecliptic as it arcs high through this southern hemisphere night skyscape. Seen on a July winter night from Lake Taupo on New Zealand's North Island, the line-up features Venus, Regulus (alpha star of Leo), Mars, and Saturn from lower left to upper right. Just put your cursor over the picture to identify the planets and constellations. The delicate luminous glow of Zodiacal Light, sunlight scattered by dust along the ecliptic, also rises above the horizon from the lower left. Of course, defined by the path of the Sun through planet Earth's sky, the ecliptic plane rides low during July nights in the northern hemisphere's summer skies. Tomorrow, the Moon and Sun will meet on the ecliptic. Along a track across the southern Pacific Ocean, the daytime sky will feature a total solar eclipse.
Total Solar Eclipse: Times and Visibility | Webcast

 

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2010 July 11

Warped Sky: Star Trails Panorama
Credit & Copyright: Peter Ward Explanation: What's happened to the sky? A time warp, of sorts, and a digital space warp too. The time warp occurs because this image captured in a single frame a four hour exposure of the night sky. As a result, prominent star trails are visible. The space warp occurs because the picture is actually a full 360 degree panorama, horizontally compressed to fit your browser. As the Earth rotated, stars appeared to circle both the South Celestial Pole, on the left, and the North Celestial Pole, just below the horizon on the right. The image captured the sky over Mudgee, New South Wales, Australia, including the domes of two large telescopes illuminated by red lighting. A horizontally unwarped image is visible by clicking on the image.
Total Solar Eclipse Today: Times and Visibility | Webcast

 

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2010 July 12

Moons Beyond the Rings of Saturn
Credit: Cassini Imaging Team, ISS, JPL, ESA, NASA Explanation: What's happened to that moon of Saturn? Nothing -- Saturn's moon Rhea is just partly hidden behind Saturn's rings. In April, the robotic Cassini spacecraft now orbiting Saturn took this narrow-angle view looking across the Solar System's most famous rings. Rings visible in the foreground include the thin F ring on the outside and the much wider A and B rings just interior to it. Although it seems to be hovering over the rings, Saturn's moon Janus is actually far behind them. Janus is one of Saturn's smaller moons and measures only about 180 kilometers across. Farther out from the camera is the heavily cratered Rhea, a much larger moon measuring 1,500 kilometers across. The top of Rhea is visible only through gaps in the rings. The Cassini mission around Saturn has been extended to 2017 to better study the complex planetary system as its season changes from equinox to solstice.





 
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monza

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2010 July 13

Mosaic: Welcome to Planet Earth
Credit: Apollo 17 Crew, NASA; Photographic Mosaic & Digital Copyright: Rob Stevenson Explanation: Welcome to Planet Earth, the third planet from a star named the Sun. The Earth is shaped like a sphere and composed mostly of rock. Over 70 percent of the Earth's surface is water. The planet has a relatively thin atmosphere composed mostly of nitrogen and oxygen. This picture of Earth, dubbed Blue Marble, was taken from Apollo 17 in 1972 and features Africa and Antarctica. It is thought to be one of the most widely distributed photographs of any kind. Here, the world famous image has been recast as a spectacular photomosaic using over 5,000 archived images of Earth and space. With its abundance of liquid water, Earth supports a large variety of life forms, including potentially intelligent species such as dolphins and humans. Please enjoy your stay on Planet Earth.


 

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2010 July 14

Easter Island Eclipse
Credit & Copyright: Stéphane Guisard (Los Cielos de America), TWAN Explanation: Makemake, a god in Easter Island mythology, may have smiled for a moment as clouds parted long enough to reveal this glimpse of July 11's total solar eclipse to skygazers. In the foreground of the dramatic scene, the island's famous large, monolithic statues (Moai) share a beachside view of the shimmering solar corona and the darkened daytime sky. Other opportunities to see the total phase of this eclipse of the Sun were also hard to come by. Defined by the dark part of the Moon's shadow, the path of totality tracked eastward across the southern Pacific Ocean, only making significant landfall at Mangaia (Cook Islands) and Easter Island (Isla de Pascua), ending shortly after reaching southern Chile and Argentina. But a partial eclipse phase could be enjoyed over a broader region, including many southern Pacific islands and wide swath of South America.


 
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