NASA's A.P.O.D.

IC 1848: The Soul Nebula Image Credit & Copyright: Bob...

Sun, 21 Apr 2013 14:01:00 -0400

IC 1848: The Soul Nebula
Image Credit & Copyright: Bob Andersson

Explanation: 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 above image appears mostly red due to the emission of a specific color of light emitted by excited hydrogen gas.

Crescent Neptune and Triton Image...

Sat, 20 Apr 2013 19:00:49 -0400

Crescent Neptune and Triton
Image Credit: Voyager 2, NASA

Explanation: Gliding silently through the outer Solar System, the Voyager 2 spacecraft camera captured Neptune and Triton together in crescent phase in 1989. The elegant picture of the gas giant planet and its cloudy moon was taken from behind just after closest approach. It could not have been taken from Earth because Neptune never shows a crescent phase to sunward Earth. The unusual vantage point also robs Neptune of its familiar blue hue, as sunlight seen from here is scattered forward, and so is reddened like thesetting Sun. Neptune is smaller but more massive than Uranus, has several dark rings, and emits more light than it receives from the Sun.

Sun with Solar Flare Image Credit: NASA Solar Dynamics...

Sat, 20 Apr 2013 14:00:47 -0400

Sun with Solar Flare
Image Credit: NASA Solar Dynamics Observatory

Explanation: This week the Sun gave up its strongest solar flare so far in 2013, accompanied by a coronal mass ejection (CME) headed toward planet Earth. A false-color composite image in extreme ultraviolet light from the Solar Dynamics Observatory captures the moment, recorded on April 11 at 0711 UTC. The flash, a moderate, M6.5 class flare erupting from active region AR 11719, is near the center of the solar disk. Other active regions, areas of intense magnetic fields seen as sunspot groups in visible light, mottle the surface as the solar maximum approaches. Loops and arcs of glowing plasma trace the active regions’ magnetic field lines. A massive cloud of energetic, charged particles, the CME will impact the Earth’s magnetosphere by this weekend and skywatchers should be on the alert for auroral displays.

Yuri’s Planet Image Credit: ISS Expedition...

Fri, 19 Apr 2013 19:00:46 -0400

Yuri’s Planet
Image Credit: ISS Expedition 30, NASA

Explanation: On another April 12th, in 1961, Soviet cosmonaut Yuri Alexseyevich Gagarin became the first human to see planet Earth from space. Commenting on his view from orbit he reported, “The sky is very dark; the Earth is bluish. Everything is seen very clearly”. On yet another April 12th, in 1981 NASA launched the first space shuttle. To celebrate in 2013, consider this image from the orbiting International Space Station, a stunning view of the planet at night from low Earth orbit. Constellations of lights connecting the densely populated cities along the Atlantic east coast of the United States are framed by two Russian spacecraft docked at the space station. Easy to recognize cities include New York City and Long Island at the right. From there, track toward the left for Philadelphia, Baltimore, and then Washington DC near picture center.

Darkened City Image Credit & Copyright: Photo Thierry...

Fri, 19 Apr 2013 14:00:57 -0400

Darkened City
Image Credit & Copyright: Photo Thierry Cohen / Courtesy Danziger Gallery, New York

Explanation: In a haunting vista you can never see, bright stars and the central Milky Way rise over the dark skyline of metropolitanPudong in Shanghai, China. Looking east across the Huangpu River, the cityscape includes Pudong’s 470 meter tall Oriental Pearl Tower. The night sky stretches from Antares and the stars of Scorpius at the far right, to Altair in Aquila at the left. To create the vision of an unseen reality, part of a series of Darkened Cities, photographer Thierry Cohen has combined a daytime image of the city skyline with an image matched in orientation from a dark sky region at the same latitude, just west of Merzouga, Morocco. The result finds the night sky that hours earlier also arced over Shanghai, but drowned in the lights of a city upon the sea.

Space Station Lookout Image Credit & Copyright: Chris...

Thu, 18 Apr 2013 19:01:08 -0400

Space Station Lookout
Image Credit & Copyright: Chris Hadfield (CSA); Annotation assistance: Vincent Berseth

Explanation: If you glanced out a side window of the International Space Station, what might you see? If you were Expedition 34flight engineer Chris Hadfield, and you were looking out one of windows of Japan’s Kibo Research Module on February 26, you might have seen the above vista. In the distance lies the darkness of outer space and the blueness of planet Earth. Large ISS objects include long solar panels that stretch diagonally from the upper left and the cylindrical airlock of the Pressurized Module that occupies the lower right. Numerous ports and platforms of the space station are visible and labeled on an annotated companion image. Of particular note is what looks to be a washer - dryer pair toward the image left, which are really NASA’s HREP (near) and JAXA’sMCE (far) research platforms. The gold foil covered experiment in the rear of HREP is the Remote Atmospheric and Ionospheric Detection System (RAIDS) that monitors atmospheric airglow, while MCE includes the Global Lightning and Sprite Measurements(JEM-GLIMS) instrument that monitors atmospheric electrical discharges. The current Expedition 35 crew is now commanded by Colonel Hadfield and scheduled to stay aboard the space station until May.

NGC 3132: The Southern Ring Nebula Image Credit: Hubble Legacy...

Thu, 18 Apr 2013 14:00:49 -0400

NGC 3132: The Southern Ring Nebula
Image Credit: Hubble Legacy Archive, ESA, NASA; Processing - Donald Waid

Explanation: It’s the dim star, not the bright one, near the center of NGC 3132 that created this odd but beautiful planetary nebula. Nicknamed the Eight-Burst Nebula and the Southern Ring Nebula, the glowing gas originated in the outer layers of a star like our Sun. In this reprocessed color picture, the hot purplish pool of light seen surrounding this binary system is energized by the hot surface of the faint star. Although photographed to explore unusual symmetries, it’s the asymmetries that help make this planetary nebula so intriguing. Neither the unusual shape of the surrounding cooler shell nor the structure and placements of the cool filamentary dust lanesrunning across NGC 3132 are well understood.

A Redshift Lookup Table for our Universe Image Credit: Sergey V....

Wed, 17 Apr 2013 19:01:05 -0400

A Redshift Lookup Table for our Universe
Image Credit: Sergey V. Pilipenko (LPI, MIPT)

Explanation: How far away is “redshift six”? Although humans are inherently familiar with distance and time, what is actually measured for astronomical objects is redshift, a color displacement that depends on exactly how energy density has evolved in our universe. Now since cosmological measurements in recent years have led to a concordance on what energy forms pervade our universe, it is now possible to make a simple table relating observed cosmological redshift, labeled “z”, with standard concepts of distance and time, including the extrapolated time since the universe began. One such table is listed above, where redshift z is listed in the first and last columns, while the corresponding universe age in billions of years is listed in the central column. To find the meaning of the rest of the columns, please read the accompanying technical paper. Although stars in our galaxy are effectively at cosmological redshift zero, the most distant supernovae seen occur out past redshift one, which the above chart shows occurred when the universe was approximately half its present age. By contrast, the most distant gamma-ray bursts yet observed occur out past redshift six, occurring when the universe was younger than one billion years old, less than 10 percent of its present age.

The Moon’s Saturn Image Credit & Copyright: Jens...

Wed, 17 Apr 2013 14:01:02 -0400

The Moon’s Saturn
Image Credit & Copyright: Jens Hackmann

Explanation: Just days after sharing the western evening sky with Venus in 2007, the Moon moved on to Saturn - actually passing in front of the ringed planet Saturn when viewed in skies over Europe, northern Africa, and western Asia. Because the Moon and bright planets wander through the sky near the ecliptic plane, such occultation events are not uncommon, but they are dramatic, especially in telescopic views. For example, in this sharp image Saturn is captured emerging from behind the Moon, giving the illusion that it lies just beyond the Moon’s bright edge. Of course, the Moon is a mere 400 thousand kilometers away, compared to Saturn’s distance of 1.4 billion kilometers. Taken with a digital camera and 20 inch diameter telescope at the Weikersheim Observatory in southern Germany, the picture is a single exposure adjusted to reduce the difference in brightness between Saturn and the cratered lunar surface.

Earth at Twilight Image Credit: ISS Expedition 2 Crew, Gateway...

Tue, 16 Apr 2013 19:00:50 -0400

Earth at Twilight
Image Credit: ISS Expedition 2 Crew, Gateway to Astronaut Photography of Earth, NASA

Explanation: No sudden, sharp boundary marks the passage of day into night in this gorgeous view of ocean and clouds over our fair planet Earth. Instead, the shadow line or terminator is diffuse and shows the gradual transition to darkness we experience as twilight. With the Sun illuminating the scene from the right, the cloud tops reflect gently reddened sunlight filtered through the dusty troposphere, the lowest layer of the planet’s nurturing atmosphere. A clear high altitude layer, visible along the dayside’s upper edge,scatters blue sunlight and fades into the blackness of space. This picture actually is a single digital photograph taken in June of 2001 from the International Space Station orbiting at an altitude of 211 nautical miles.

Comet of the North Image Credit & Copyright: P-M Hedén...

Tue, 16 Apr 2013 14:00:42 -0400

Comet of the North
Image Credit & Copyright: P-M Hedén (Clear Skies, TWAN)

Explanation: It looks like a double comet, but Comet PanSTARRS (C/2011 L4) is just offering skygazers a Messier moment. Outward bound and fading in this starry scene, the well-photographed comet is remarkably similar in brightness to M31, the Andromeda Galaxy. Tracking through northern skies just below the galaxy, the comet was captured as local midnight approached on April 3. Both comet and galaxy were visible to the eye and are immersed in the faint glow of northern lights. Our own Milky Way galaxy arcs over the snowy field near Tänndalen, Sweden. Double star cluster h and chi Persei can be spotted along the Milky Way’s arc high above the comet/galaxy pair. Follow the arc to bright Deneb, alpha star of the constellation Cygnus, at the right edge of the frame.

M64: The Black Eye Galaxy Image Credit & Copyright: Martin...

Mon, 15 Apr 2013 19:01:28 -0400

M64: The Black Eye Galaxy
Image Credit & Copyright: Martin Pugh

Explanation: This beautiful, bright, spiral galaxy is Messier 64, often called the Black Eye Galaxy or the Sleeping Beauty Galaxy for its heavy-lidded appearance in telescopic views. M64 is about 17 million light-years distant in the otherwise well-groomed northern constellation Coma Berenices. In fact, the Red Eye Galaxy might also be an appropriate moniker in this colorful composition of narrow and wideband images. The enormous dust clouds obscuring the near-side of M64’s central region are laced with the telltale reddish glow of hydrogen associated with star forming regions. But they are not this galaxy’s only peculiar feature. Observations show that M64 is actually composed of two concentric, counter-rotating systems. While all the stars in M64 rotate in the same direction as the interstellar gas in the galaxy’s central region, gas in the outer regions, extending to about 40,000 light-years, rotates in the opposite direction. The dusty eye and bizarre rotation is likely the result of a billion year old merger of two different galaxies.

Comet PANSTARRS and the Andromeda Galaxy Image Credit &...

Thu, 04 Apr 2013 19:01:10 -0400

Comet PANSTARRS and the Andromeda Galaxy
Image Credit & Copyright: Pavel Smilyk

Explanation: Currently, comet PANSTARRS is passing nearly in front of the galaxy Andromeda. Coincidentally, both comet and galaxyappear now to be just about the same angular size. In physical size, even though Comet PANSTARRS is currently the largest object in theSolar System with a tail spanning about 15 times the diameter of the Sun, it is still about 70 billion times smaller than the Andromeda galaxy(M31). The above image was captured on March 30, near Syktyvkar, Russia. As C/2011 L4 (PANSTARRS) on the lower left recedesfrom the Sun and dims, it is returning to the northerly direction whence it came. When the comet will return is currently unknown, althoughhumans may have merged with computers by then.

IC 4592: The Blue Horsehead Reflection Nebula Image Credit &...

Thu, 04 Apr 2013 14:00:41 -0400

IC 4592: The Blue Horsehead Reflection Nebula
Image Credit & Copyright: Scott Rosen

Explanation: Do you see the horse’s head? What you are seeing is not the famous Horsehead nebula toward Orion but rather a fainter nebula that only takes on a familiar form with deeper imaging. The main part of the above imaged molecular cloud complex is a reflection nebula cataloged as IC 4592. Reflection nebulas are actually made up of very fine dust that normally appears dark but can look quite blue when reflecting the light of energetic nearby stars. In this case, the source of much of the reflected light is a star at the eye of the horse. That star is part of Nu Scorpii, one of the brighter star systems toward the constellation of the Scorpion Scorpius. A second reflection nebuladubbed IC 4601 is visible surrounding two stars on the upper right of the image center.

Moon or Frying Pan? Images Credit: Frying Pan...

Tue, 02 Apr 2013 19:01:00 -0400

Moon or Frying Pan?
Images Credit: Frying Pan (Copyrighted): Christopher Jonassen; Moon: NASA

Explanation: Which is which? Of the two images shown above, one is a moon in our Solar System, while the other is the bottom of frying pan. We are not making this up — can you tell a pan from a planetoid? Think you got it? To find the answer click here. OK, but there are more! That’s right: you, your family, friends, neighbors, and local elected officials can all play “Moon or Frying Pan” with these other image pairs, too. As everyone knows, the fundamental underlying reason why moons and frying pans appear similar is — OK, we at APOD aren’t sure either. And if you’ve b e e n f o o l e d, don’t fret — just remember that it’s OK because today is April Fool’s Day.

Flying Over the Earth at Night Video Credit: Gateway to...

Tue, 02 Apr 2013 14:00:52 -0400

Flying Over the Earth at Night
Video Credit: Gateway to Astronaut Photography, NASA ; Compilation: David Peterson (YouTube);
Music: Freedom Fighters (Two Steps from Hell)

Explanation: Many wonders are visible when flying over the Earth at night. A compilation of such visual spectacles was captured recently from theInternational Space Station (ISS) and set to rousing music. Passing below are white clouds, orange city lights, lightning flashes in thunderstorms, and darkblue seas. On the horizon is the golden haze of Earth’s thin atmosphere, frequently decorated by dancing auroras as the video progresses. The green parts of auroras typically remain below the space station, but the station flies right through the red and purple auroral peaks. Solar panels of the ISS are seen around the frame edges. The ominous wave of approaching brightness at the end of each sequence is just the dawn of the sunlit half of Earth, a dawn that occursevery 90 minutes.

The Broad Tail of PanSTARRS Image Credit...

Mon, 01 Apr 2013 19:00:51 -0400

The Broad Tail of PanSTARRS
Image Credit & Copyright: Lorenzo Comolli - Model Overlay: Marco Fulle (INAF)

Explanation: For northern hemisphere skygazers, fading Comet PanSTARRS (C/2011 L4) still hangs above the western horzion, after sunset but before moonrise in the coming days. Its perspective from planet Earth continues to reveal the comet’s broad dust tail. This long exposure tracking the comet, made on March 21, has been enhanced to show remarkable, subtle striations in PanSTARRS’ tail. Place your cursor over the image (or click here) to show an overlay of the dust tail with a model network of synchrones and syndynes. Synchrones (long dashed lines) trace the location of dust grains released from the comet nucleus at the same time and with zero velocity. The successive synchrone lines shown are separated by 1 day and start at the bottom, 10 days before the comet’s March 10 perihelion passage. Syndynes (solid lines) show the location of dust grains of the same size, also released with zero velocity. Dust grains 1 micron wide lie along the upper syndyne. The grain width increases counterclockwise to 500 micron wide grains along the syndyne nearly parallel to the comet’s orbit (short dashed line through the nucleus location). In the model, forces acting on the dust grains were assumed to be gravity and the pressure of sunlight. The periodic striations in PanSTARRS’ tail seem to closely follow the model synchrone lines.

Ringside with Rhea Image Credit: Cassini Imaging...

Sun, 31 Mar 2013 14:00:43 -0400

Ringside with Rhea
Image Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA

Explanation: Orbiting in the plane of Saturn’s rings, Saturnian moons have a perpetual ringside view of the gas giant planet. Of course, while passing near the ring plane the Cassini spacecraft also shares their stunning perspective. The thin rings themselves slice across the middle of this Cassini snapshot from April 2011. The scene looks toward the dark night side of Saturn, in the frame at the left, and the still sunlit side of the rings from just above the ringplane. Centered, over 1,500 kilometers across, Rhea is Saturn’s second largest moon and is closest to the spacecraft, around 2.2 million kilometers away. To Rhea’s right, shiny, 500 kilometer diameter Enceladus is about 3 million kilometers distant. Dione, 1,100 kilometers wide, is 3.1 million kilometers from Cassini’s camera on the left, partly blocked by Saturn’s night side.

Unraveling NGC 3169 Image Credit & Copyright: Adam...

Sat, 30 Mar 2013 19:00:45 -0400

Unraveling NGC 3169
Image Credit & Copyright: Adam Block, Mt. Lemmon SkyCenter, University of Arizona

Explanation: Bright spiral galaxy NGC 3169 appears to be unraveling in this cosmic scene, played out some 70 million light-years away just belowbright star Regulus toward the faint constellation Sextans. Its beautiful spiral arms are distorted into sweeping tidal tails as NGC 3169 (left) and neighboring NGC 3166 interact gravitationally, a common fate even for bright galaxies in the local universe. In fact, drawn out stellar arcs and plumes, indications of gravitational interactions, seem rampant in the deep and colorful galaxy group photo. The picture spans 20 arc minutes, or about 400,000 light-years at the group’s estimated distance, and includes smaller, dimmer NGC 3165 at the right. NGC 3169 is also known to shine across the spectrum from radio to X-rays, harboring an active galactic nucleus that is likely the site of a supermassive black hole.

A Horizon Rainbow in Paris Image Credit &...

Sat, 30 Mar 2013 14:00:43 -0400

A Horizon Rainbow in Paris
Image Credit & Copyright: Bertrand Kulik

Explanation: Why is this horizon so colorful? Because, opposite the Sun, it is raining. What is pictured above is actually just a common rainbow. It’s uncommon appearance is caused by the Sun being unusually high in the sky during the rainbow’s creation. Since every rainbow’s center must be exactly opposite the Sun, a high Sun reflecting off of a distant rain will produce a low rainbow where only the very top is visible — because the rest of the rainbow is below the horizon. Furthermore, no two observers can see exactly the same rainbow — every person finds themselves exactly between the Sun and rainbow’s center, and every observer sees the colorful circular band precisely 42 degrees from rainbow’s center. The above imagefeaturing the Eiffel Tower was taken in Paris, France last week. Although the intermittent thunderstorms lasted for much of the day, the horizon rainbow lasted for only a few minutes.