NASA Astronomy Picture of the Day 2003-4

A New Constellation Takes Hold

A new constellation has taken hold of the sky, much to the surprise of many sky gazers. The constellation of Ollie the Owl has suddenly started dominating the southern hemisphere, as shown above. The constellation is taking the place of Wrinkles the Rhinoceros, who was unexpectedly voted off the sky by the other constellations. Happy April Fools day from the folks at APOD! Pictured above, a bird was photographed taking the Tololo All Sky Camera (TASCA) as a perch, a situation that would be even funnier if the bird's talons hadn't scratched the plastic enclosing dome. TASCA continues to monitor the entire night sky as visible from the Cerro Tololo Inter-american Observatory located in Chile. Given the unusual vantage point, one guess is that the bird is a Great Horned Owl, although it is hoped that a properly under-schooled ornithologist can e-mail Dr. Schwarz with the bird's true species.

V838 Light Echo: The Movie

What caused this outburst of V838 Mon? For reasons unknown, star V838 Mon's outer surface suddenly greatly expanded with the result that it became the brightest star in the entire Milky Way Galaxy. Then, just as suddenly, it faded. A stellar flash like this has never been seen before -- supernovas and novas expel matter out into space. Although the V838 Mon flash appears to expel material into space, what is seen in the above four-frame movie is actually an outwardly moving light echo of the bright flash. The actual time-span of the movie is 8 months during 2002. In a light echo, light from the flash is reflected by successively more distant rings in the complex array of ambient interstellar dust that already surrounded the star. V838 Mon lies about 20,000 light years away toward the constellation of Monoceros, while the largest light echo above spans about six light years in diameter.

Jupiter in the Hive

If you can find planet Jupiter in tonight's sky, then you can also find M44, popularly known as the Beehive star cluster. In fact, with a pair of binoculars most casual skygazers should find it easy to zero in on this celestial scene. It should be easy because after sunset Jupiter presently rules the night as the brightest "star" overhead. Now near the stationary part of its wandering path through the heavens, Jupiter will obligingly linger for a while at a spot only a degree or so southeast of M44 in the relatively faint constellation Cancer. Seen here in a photograph from March 28, Jupiter (lower left) is strongly overexposed with the stars of M44 swarming above and to the right. The picture approximately corresponds to the view when looking through a typical pair of binoculars. Jupiter is about 30 light-minutes from our fair planet while M44, one of the closest star clusters, is around 600 light-years away.

Clusters and Nebulae of the Hexagon

At first, the bright stars of the large asterism known as the (northern) Winter Hexagon might be hard to pick out in this gorgeous deep sky mosaic from December 2002. But placing your cursor over the picture will reveal the hexagon's outlines and the bright clusters and nebulae along a stunning portion of the Milky Way opposite the galactic center. The celestial highlights include M42 (aka the Great Nebula of Orion), Orion's Horsehead nebula, the Rosette and Cone nebulae, and nearby star clusters M45 (Pleiades) and Gemini's own M35. For now, this hexagon is sinking low in western evening skies.

The Seasons of Saturn

Since Saturn's axis is tilted as it orbits the Sun, Saturn has seasons, like those of planet Earth ... but Saturn's seasons last for over seven years. So what season is it on Saturn now? Orbiting the equator, the tilt of the rings of Saturn provides quite a graphic seasonal display. In fact, this month, Saturn's rings will reach their most "open" angle after appearing nearly edge on in the mid-1990s. The ringed planet is also well placed in evening skies providing a grand view as summer comes to Saturn's southern hemisphere and winter to the north. The Hubble Space Telescope took the above sequence of images about a year apart, starting on the left in 1996 and ending on the right in 2000. Although they look solid, Saturn's Rings are likely less than 50 meters thick and consist of individually orbiting bits of ice and rock ranging in size from grains of sand to barn-sized boulders.

Phobos: Doomed Moon of Mars

This moon is doomed. Mars, the red planet named for the Roman god of war, has two tiny moons, Phobos and Deimos, whose names are derived from the Greek for Fear and Panic. These Martian moons may well be captured asteroids originating in the main asteroid belt between Mars and Jupiter or perhaps from even more distant reaches of the Solar System. In this 1978 Viking 1 orbiter image, the largest moon, Phobos, is indeed seen to be a heavily cratered asteroid-like object. About 17 miles across, Phobos really zips through the Martian sky. Actually rising above Mars' western horizon and setting in the east, it completes an orbit in less than 8 hours. But Phobos orbits so close to Mars, (about 5,800 kilometers above the surface compared to 400,000 kilometers for our Moon) that gravitational tidal forces are dragging it down. In 100 million years or so it will likely crash into the surface or be shattered by stress caused by the relentless tidal forces, the debris forming a ring around Mars.

NGC 281: Cluster, Clouds, and Globules

NGC 281 is a busy workshop of star formation. Prominent features include a small open cluster of stars, a diffuse red-glowing emission nebula, large lanes of obscuring gas and dust, and dense knots of dust and gas in which stars may still be forming. The open cluster of stars IC 1590 visible around the center has formed only in the last few million years. The brightest member of this cluster is actually a multiple-star system shining light that helps ionize the nebula's gas, causing the red glow visible throughout. The lanes of dust visible below the center are likely homes of future star formation. Particularly striking in the above photograph are the dark Bok globules visible against the bright nebula. Stars are surely forming there right now. The entire NGC 281 system lies about 10 thousand light years distant. Have you seen today's: Earth Science Picture of the Day?

Aurora From Space

What do auroras look like from space? From the ground, auroras dance high above clouds, frequently causing spectacular displays. The International Space Station (ISS) orbits just at the same height as many auroras, though. Therefore, sometimes it flies over them, but also sometimes it flies right through. The auroral electron and proton streams are too thin to be a danger to the ISS, just as clouds pose little danger to airplanes. ISS Science Officer Don Pettit captured a green aurora, pictured above in a digitally sharpened image. From orbit, Dr. Pettit reports, changing auroras can appear to crawl around like giant green amoebas. Far below, on planet Earth, the Manicouagan Impact Crater can be seen in northern Canada. Have you seen today's: Space Station Science Picture of the Day?

The Egg Nebula in Polarized Light

Where is the center of the unusual Egg Nebula? Like a baby chick pecking its way out of an egg, the star in the center of the Egg Nebula is casting away shells of gas and dust as it slowly transforms itself into a white dwarf star. The Egg Nebula is a rapidly evolving pre-planetary nebula spanning about one light year toward the constellation of Cygnus. Thick dust, though, blocks the center star from view, while the dust shells further out reflect light from this star. Light vibrating in the plane defined by each dust grain, the central star, and the observer is preferentially reflected, causing an effect known as polarization. Measuring the orientation of the polarized light for the Egg Nebula gives clues to location of the hidden source. The above image taken by the Advanced Camera for Surveys on the Hubble Space Telescope is false-color coded to highlight the orientation of polarization. Have you seen this week's: HEASARC Picture of the Week?

Energized Nebula in the LMC

Blossoming in nearby galaxy the Large Magellanic Cloud (LMC), this gorgeous nebula is energized by radiation and winds from a massive star whose surface temperature approaches 100,000 degrees. The composite color image from the European Southern Observatory's Melipal telescope resolves details in the energetic nebula, with emission from helium atoms in blue hues, oxygen atoms in green, and hydrogen atoms in red. While emission nebulae generally show the familiar red light from ionized hydrogen atoms - hydrogen atoms with their electrons stripped away - ionized helium atoms are tracers of even higher energy interactions. The intriguing filaments of helium emission make this and other recently studied emission nebulae most exceptional. A Wolf-Rayet star, the massive star powering this nebula, created a cosmic bubble with stellar winds in the early stages of its life. Part of the bubble is still apparent as the large arc in the lower portion of the image. The area pictured is about 150 light-years across. Have you seen today's: THEMIS Image of Mars?

London at Night

Do you recognize this intriguing globular cluster of stars? It's actually the constellation of city lights surrounding London, England, planet Earth, as recorded with a digital camera from the International Space Station. Taken in February 2003, north is toward the top and slightly left in this nighttime view. The encircling "London Orbital" highway by-pass, the M25 (... but not Messier 25), is easiest to pick out south of the city. Even farther south are the lights of Gatwick airport and just inside the western (left hand) stretch of the Orbital is Heathrow. The darkened Thames river estuary fans out to the city's east. In particular, two small "dark nebulae" - Hyde Park and Regents Park - stand out slightly west of the densely packed lights at the city's core. Have you seen this: NASA Image of the Day?

Mercury on the Horizon

Have you ever seen the planet Mercury? Because Mercury orbits so close to the Sun, it never wanders far from the Sun in Earth's sky. If trailing the Sun, Mercury will be visible low on the horizon for only a short while after sunset. If leading the Sun, Mercury will be visible only shortly before sunrise. So at certain times of the year an informed skygazer with a little determination can usually pick Mercury out from a site with an unobscured horizon. Above, a lot of determination has been combined with a little digital trickery to show Mercury's successive positions during March of 2000. Each picture was taken from the same location in Spain when the Sun itself was 10 degrees below the horizon and superposed on the single most photogenic sunset. By the middle of this month, Mercury will again be well placed for viewing above the western horizon at sunset, but by the end of April it will have faded and dropped into the twilight. On May 7th, Mercury will cross the Sun's disk.

NGC 1365: A Nearby Barred Spiral Galaxy

Many spiral galaxies have bars across their centers. Even our own Milky Way Galaxy is thought to have a bar, but perhaps not so prominent as the one in NGC 1365, shown above. The persistence and motion of the bar imply relatively massive spiral arms. The placements of bright young blue stars and dark dust lanes also indicate a strong rotating density wave of star formation. NGC 1365 is a member of the Fornax Cluster of Galaxies. Because NGC 1365 is relatively nearby, simultaneous measurements of its speed and distance are possible, which help astronomers estimate how fast our universe is expanding.

A Gamma Ray Burst - Supernova Connection

New evidence has emerged that a mysterious type of explosion known as a gamma ray burst is indeed connected to a supernova of the type visible in the above image. Two weeks ago, the orbiting HETE satellite detected gamma-ray burst GRB030329. The extremely bright burst was found hours later to have an extremely bright afterglow in visible light, and soon set the record for the closest measured distance at redshift 0.17. The afterglow brightness allows unprecedented coverage of its evolution. Just this week, as many astronomers suspected would happen, the afterglow began to appear as a fading Type II Supernova. Type II Supernovas might not appear coincident with gamma-ray bursts, however, when the gamma-ray beam goes in another direction. The above spiral galaxy, NGC 3184, was home to a Type II Supernova in 1999 at the position of the arrow. Astronomers are currently pressing hard to find the host galaxy for GRB030329.

A Crescent Nebula Star Field

What caused the Crescent Nebula? Looking like an emerging space cocoon, the Crescent Nebula, visible on the right, was created by the brightest star in its center. A leading progenitor hypothesis has the Crescent Nebula beginning to form about 250,000 years ago. At that time, the massive central star had evolved to become a Wolf-Rayet star (WR 136), shedding its outer envelope in a strong stellar wind, ejecting the equivalent of our Sun's mass every 10,000 years. This wind impacted surrounding gas left over from a previous phase, compacting it into a series of complex shells, and lighting it up. The Crescent Nebula, also known as NGC 6888, lies about 4,700 light-years away in the constellation of Cygnus. Star WR 136 will probably undergo a supernova explosion sometime in the next million years.

Magma Bubbles from Mt. Etna

Mt. Etna erupted spectacularly in 2001 June. Pictured above, the volcano was photographed expelling bubbles of hot magma, some of which measured over one meter across. One reason planetary geologists study Earth's Mt. Etna is because of its likely similarity to volcanoes on Mars. Mt. Etna, a basalt volcano, is composed of material similar to Mars, and produces similar lava channels. Located in Sicily, Italy, Mt. Etna is not only one of the most active volcanoes on Earth, it is one of the largest, measuring over 50 kilometers at its base and rising nearly 3 kilometers high.

M106 in Canes Venatici

Close to the Great Bear (Ursa Major) and surrounded by the stars of the Hunting Dogs (Canes Venatici), this celestial nebula was discovered in 1781 by the metric French astronomer Pierre Mechain and later added to the catalog of his friend and colleague Charles Messier as M106. Modern deep telescopic views reveal it to be an island universe -- a spiral galaxy around 30 thousand light-years across located only about 21 million light-years beyond the stars of the Milky Way. Youthful blue star clusters and reddish stellar nurseries trace the striking spiral arms of M106. Seen so clearly in this beautiful image, the galaxy's bright core is also visible across the spectrum from radio to x-rays, making M106 a nearby example of the Seyfert class of active galaxies. The bright core of a Seyfert galaxy is believed to be powered by matter falling into a massive central black hole.

Double Eruptive Prominences

Lofted over the Sun on looping magnetic fields, large solar prominences are composed of relatively cool, dense plasma. When seen against the brilliant solar disk they appear as dark filaments, but these enormous magnetic structures are bright themselves when viewed against the blackness of space as they arc above the Sun's edge. In a rare visual treat, these two solar prominences arising from the Sun's southern (lower) hemisphere were captured in extreme ultraviolet light by the EIT camera on board the space-based SOlar and Heliospheric Observatory (SOHO) on March 21. For scale, the pair of plasma loops stretch above the Sun to a height of about twenty times the diameter of planet Earth. In a matter of hours, these prominences apparently erupted away from the Sun's surface and may have been associated with a flare and coronal mass ejection.

Spiral Galaxy In Centaurus

Centaurus, the Centaur, is one of the most striking constellations in the southern sky. The lovely Milky Way flows through this large constellation whose celestial wonders also include the closest star to the sun, Alpha Centauri, the largest globular star cluster in our galaxy, Omega Centauri, and the closest active galaxy, Centaurus A. Embraced by tightly wound spiral arms of bright blue star clusters, this gorgeous galaxy - cataloged as ESO 269-57 - also falls within Centaurus' borders. Seen behind a veil of foreground stars which lie within our own galaxy, this face-on spiral galaxy is about 150 million light-years away and 200,000 light-years across. The brighter foreground stars are marked by diffraction spikes caused by the telescope and yellow vertical stripes due to saturated digital camera pixels in the above Very Large Telescope image from the European Southern Observatory. Tantalizing wisps of more distant, faint galaxies are visible in the background.

The Gum Nebula Supernova Remnant

Because the Gum Nebula is the closest supernova remnant, it is actually hard to see. Spanning 40 degrees across the sky, the nebula is so large and faint it is easily lost in the din of a bright and complex background. The Gum Nebula, highlighted nicely in the above wide angle photograph, is so close that we are much nearer the front edge than the back edge, each measuring 450 and 1500 light years respectively. The complex nebula lies in the direction of the constellations of Puppis and Vela. Oddly, much remains unknown about the Gum Nebula, including the timing and even number of supernova explosions that formed it.

A Halo Around the Moon

Tomorrow's picture: North Mars < | Archive | Index | Search | Calendar | Glossary | Education | About APOD | > Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Web Site Statements, Warnings, and Disclaimers NASA Official: Jay Norris. Specific rights apply. A service of: LHEA at NASA / GSFC & Michigan Tech. U.

Springtime on Mars

Vast canyons, towering volcanoes, sprawling fields of ice, deep craters, and high clouds can all be seen in this image of the Solar System's fourth planet: Mars. The orbiting robot Mars Global Surveyor spacecraft took the above mosaic of images as springtime dawned in Northern Mars in 2002 May. Sprawled across the image bottom is Valles Marinaris, a canyon three times the length of Earth's Grand Canyon, and four times as deep. On the left are several volcanoes including Olympus Mons, a volcano three times higher than Earth's Mt. Everest. At the top is the North Polar Cap made of thawing water and carbon-dioxide based ice. Swirling white clouds and circular impact craters are also visible around Mars. Two rovers will be launched to Mars this summer and should arrive in 2004 January.

The Stars of NGC 1705

Some 2,000 light-years across, NGC 1705 is small as galaxies go, similar to our Milky Way's own satellite galaxies, the Magellanic Clouds. At a much larger distance of 17 million light-years, the stars of NGC 1705 are still easily resolved in this beautiful image constructed from data taken in 1999 and 2000 with the Hubble Space Telescope. Most of the younger, hot, blue stars in the galaxy are seen to be concentrated in a large central star cluster with the older, cooler, red stars more evenly distributed. Possibly 13 billion years old, NGC 1705 could well have been forming stars through out its lifetime while light from its most recent burst of star formation reached Earth only 30 million years ago. This gradually evolving dwarf irregular galaxy lacks organized structures like spiral arms and is thought to be a nearby analog to the first galaxies to form in the early Universe.

Earth at Twilight

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.

M17: A Hubble Close-Up

Sculpted by stellar winds and radiation, these fantastic, undulating shapes lie within the stellar nursery known as M17, the Omega Nebula, some 5,500 light-years away in the nebula-rich constellation Sagittarius. The lumpy features in the dense cold gas and dust are illuminated by stars off the upper left of the image and may themselves represent sites of future star formation. Colors in the fog of surrounding hotter material indicate M17's chemical make up. The predominately green glow corresponds to abundant hydrogen, with trace sulfur and oxygen atoms contributing red and blue hues. The picture spans about 3 light-years and was released to celebrate the thirteenth year of the Hubble Space Telescope's cosmic voyage of exploration.

Big Blue Marble Earth

This reconstructed digital portrait of our planet is reminiscent of the Apollo-era pictures of the "big blue marble" Earth from space. To create it, researchers at Goddard Space Flight Center's Laboratory for Atmospheres combined data from a Geostationary Operational Environmental Satellite (GOES), the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), and the Polar Orbiting Environmental Satellites (POES) with a USGS elevation model of Earth's topography. Stunningly detailed, the planet's western hemisphere is cast so that heavy vegetation is green and sparse vegetation is yellow, while the heights of mountains and depths of valleys have been exaggerated by 50 times to make vertical relief visible. Hurricane Linda is the dramatic storm off North America's west coast. And what about the Moon? The lunar image was reconstructed from GOES data and artistically rescaled for this visualization.

Venus' Once Molten Surface

If you could look at Venus with radar eyes - this is what you might see. This computer reconstruction of the surface of Venus was created from data from the Magellan spacecraft. Magellan orbited Venus and used radar to map our neighboring planet's surface between 1990 and 1994. Magellan found many interesting surface features, including the large circular domes, typically 25-kilometers across, that are depicted above. Volcanism is thought to have created the domes, although the precise mechanism remains unknown. Venus' surface is so hot and hostile that no surface probe has lasted more than a few minutes.

Rollout of a Soyuz TMA-2 Aboard an R7 Rocket

It takes a big rocket to go into space. Last weekend, this huge Russian rocket was launched toward Earth-orbiting International Space Station (ISS), carrying two astronauts who will make up the new Expedition 7 crew. Seen here during rollout at the Baikonur Cosmodrome, the rocket's white top is actually a Soyuz TMA-2, the most recent version of the longest serving type of human spacecraft. The base is a Russian R7 rocket, originally developed as a prototype Intercontinental Ballistic Missile in 1957. The rocket spans the width of a football field and has a fueled mass of about half a million kilograms. Russian rockets like this will be primary transportation system to the ISS while NASA studies the underlying reasons behind the recent tragic break-up of the Space Shuttle Columbia.

In the Center of the Rosette Nebula

In the heart of the Rosette Nebula lies a bright open cluster of stars that lights up the nebula. The stars of NGC 2244 formed from the surrounding gas only a few million years ago. This just-released image taken by the CFHT's new MegaPrime camera shows the region in unprecedented detail. Although the emission nebula is dominated by red hydrogen light, the above image has exaggerated the effect of green light emitted primarily by small amounts of oxygen. A hot wind of particles streams away from the cluster stars and contributes to an already complex menagerie of gas and dust filaments while slowly evacuating the cluster center. The Rosette Nebula's center measures about 50 light-years across, lies about 4500 light-years away, and is visible with binoculars towards the constellation of Monoceros.

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