科普 神奇的宇宙----图片(每天更新中)

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Clouds and Sand on the Horizon of Mars

Explanation: If you could stand on Mars -- what might you see? Like the robotic Opportunity rover rolling across the red planet, you might well see vast plains of red sand, an orange tinted sky, and wispy light clouds. The Opportunity rover captured just such a vista after arriving at Victoria Crater earlier this month, albeit in a completely different direction from the large crater. Unlike other Martian vistas, few rocks are visible in this exaggerated color image mosaic. The distant red horizon is so flat and featureless that it appears similar to the horizon toward a calm blue ocean on Earth. Clouds on Mars can be composed of either carbon dioxide ice or water ice, and can move quickly, like clouds move on Earth. The red dust in the Martian air can change the sky color above Mars from the blue that occurs above Earth toward the red, with the exact color depending on the density and particle size of the floating dust particles.

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In the Shadow of Saturn

Explanation: In the shadow of Saturn, unexpected wonders appear. The robotic Cassini spacecraft now orbiting Saturn recently drifted in giant planet's shadow for about 12 hours and looked back toward the eclipsed Sun. Cassini saw a view unlike any other. First, the night side of Saturn is seen to be partly lit by light reflected from its own majestic ring system. Next, the rings themselves appear dark when silhouetted against Saturn, but quite bright when viewed away from Saturn and slightly scattering sunlight, in the above exaggerated color image. Saturn's rings light up so much that new rings were discovered, although they are hard to see in the above image. Visible in spectacular detail, however, is Saturn's E ring, the ring created by the newly discovered ice-fountains of the moon Enceladus, and the outermost ring visible above. Far in the distance, visible on the image left just above the bright main rings, is the almost ignorable pale blue dot of Earth.

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An Orion Deep Field

Explanation: Adrift 1,500 light-years away in one of the night sky's most recognizable constellations, the glowing Orion Nebula and the dark Horsehead Nebula are contrasting cosmic vistas. They both appear in this stunning composite digital image assembled from over 20 hours of data that includes exposures filtered to record emission from hydrogen atoms. The view reveals extensive nebulosities associated with the giant Orion Molecular Cloud complex, itself hundreds of light-years across. The magnificent emission region, the Orion Nebula (aka M42), lies at the upper right of the picture. Immediately to its left are a cluster of of prominent bluish reflection nebulae sometimes called the Running Man. The Horsehead nebula appears as a dark cloud, a small silhouette notched against the long red glow at the lower left. Alnitak is the easternmost star in Orion's belt and is seen as the brightest star to the left of the Horsehead. Below Alnitak is the Flame Nebula, with clouds of bright emission and dramatic dark dust lanes. Fainter tendrils of glowing hydrogen gas are easily traced throughout the region in this Orion deep field.

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The Hubble SWEEPS Field

Explanation: This crowded star field towards the center of our Milky Way Galaxy turns out to be a great place to search for planets beyond our solar system. In fact, repeatedly imaging about 180,000 stars in the field over a one week period, the Hubble Space Telescope enabled astronomers to conduct the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS). Their search looked for brief, periodic dips in brightness caused as a large planet eclipses or transits its parent star. Since chances of seeing such an eclipse are slim, it was a definite advantage to examine as many stars as possible. In the end, SWEEPS astronomers found 16 candidate stars (green circles identify 11 in this cropped picture) that are likely closely orbited by large Jupiter-sized planets with periods of a few days or less. Large planets orbiting so close to their stars are termed hot Jupiters. Kepler, a future NASA mission, is intended to extend the transit technique to search for Earth-sized planets.

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Saturn's Infrared Glow

Explanation: Known for its bright ring system and many moons, gas giant Saturn looks strange and unfamiliar in this false-color view from the Cassini spacecraft. In fact, in this Visual and Infrared Mapping Spectrometer (VIMS) mosaic the famous rings are almost invisible, seen edge-on cutting across picture center. The most striking contrast in the image is along the terminator or boundary between night and day. To the right (day side) blue-green hues are visible sunlight reflected from Saturn's cloud tops. But on the left (night side) in the absence of sunlight, the lantern-like glow of infrared radiation from the planet's warm interior silhouettes features at Saturn's deeper cloud levels. The thermal infrared glow is also apparent in the broad bands of ring shadows draped across the northern hemisphere of Saturn.

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Markarian's Chain of Galaxies

Explanation: Across the heart of the Virgo Cluster of Galaxies lies a striking string of galaxies known as Markarian's Chain. The chain, pictured above, is highlighted on the lower right with two large but featureless lenticular galaxies, M84 and M86, and connects through several large spiral to the upper left, including M88. The home Virgo Cluster is the nearest cluster of galaxies, contains over 2,000 galaxies, and has a noticeable gravitational pull on the galaxies of the Local Group of Galaxies surrounding our Milky Way Galaxy. The center of the Virgo Cluster is located about 70 million light years away toward the constellation of Virgo. At least seven galaxies in the chain appear to move coherently, although others appear to be superposed by chance. The above image is just a small part of a mosaic dubbed the Big Picture taken by the Samuel Oschin Telescope at Palomar Observatory, in California, USA. A mural of the Big Picture will be displayed at the newly renovated Griffith Observatory near Los Angeles, California.

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Reflection Nebulas in Orion

Explanation: In the vast Orion Molecular Cloud complex, several bright blue nebulas are particularly apparent. Pictured above are two of the most prominent reflection nebulas - dust clouds lit by the reflecting light of bright embedded stars. The more famous nebula is M78, near the image center, cataloged over 200 years ago. On the upper left is the lesser known NGC 2071. The image was taken with the Mayall 4-meter telescope on Kitt Peak, Arizona, USA. Astronomers continue to study these reflection nebulas to better understand how interior stars form. The Orion complex lies about 1500 light-years distant, contains the Orion and Horsehead nebulas, and covers much of the constellation of Orion.

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CMBR Dipole: Speeding Through the Universe

Explanation: Our Earth is not at rest. The Earth moves around the Sun. The Sun orbits the center of the Milky Way Galaxy. The Milky Way Galaxy orbits in the Local Group of Galaxies. The Local Group falls toward the Virgo Cluster of Galaxies. But these speeds are less than the speed that all of these objects together move relative to the cosmic microwave background radiation (CMBR). In the above all-sky map from the COBE satellite, radiation in the Earth's direction of motion appears blueshifted and hence hotter, while radiation on the opposite side of the sky is redshifted and colder. The map indicates that the Local Group moves at about 600 kilometers per second relative to this primordial radiation. This high speed was initially unexpected and its magnitude is still unexplained. Why are we moving so fast? What is out there?

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COBE All-Sky Map

Explanation: This historic all-sky map is based on the first two years of data from NASA's COsmic Background Explorer (COBE) satellite, launched in November of 1989. The map shows minute temperature variations (red is hotter) imprinted on the Cosmic Microwave Background (CMB) radiation by structures in the early Universe. These detailed measurements of the CMB and other COBE results ushered in an age of precision cosmology, and exactly confirmed the predictions of the Big Bang theory. Playing leading roles in the COBE project, for their resulting discoveries John C. Mather (NASA, Goddard Space Flight Center), and George F. Smoot (UC Berkeley) were selected to receive the 2006 Nobel Prize in Physics.

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Dusty NGC 1333

Explanation: Dusty NGC 1333 is seen in visible light as a reflection nebula, dominated by bluish hues characteristic of starlight reflected by dust. But at longer infrared wavelengths, the interstellar dust itself glows. Moving your cursor over the picture will match up a visible light view with a false-color infrared image of the region from the Spitzer Space Telescope. The penetrating infrared view unmasks youthful stars that are otherwise obscured by the dusty clouds that formed them. Also revealed are greenish streaks and splotches that seem to litter the region. The structures trace the glow of cosmic jets blasting away from emerging young stellar objects and plowing into the cold cloud material. In all, the chaotic environment likely resembles one in which our own Sun formed over 4.5 billion years ago. NGC 1333 is a mere 1,000 light-years distant in the constellation Perseus.

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Hidden Galaxy IC 342

Explanation: Similar in size to other large, bright spiral galaxies IC 342 is a mere 7 million light-years distant in the long-necked, northern constellation Camelopardalis. A sprawling island universe, IC 342 would otherwise be a prominent galaxy in our night sky, but it is almost hidden from view behind the veil of stars, gas and dust clouds in the plane of our Milky Way galaxy. Even though IC 342's light is dimmed by intervening cosmic clouds, this remarkably sharp telescopic image traces the galaxy's own obscuring dust, blue star clusters, and glowing pink star forming regions along spiral arms that wind far from the galaxy's core. IC 342 may have undergone a recent burst of star formation activity and is close enough to have gravitationally influenced the evolution of the local group of galaxies and the Milky Way.

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Twelve Lunar Eclipses

Explanation: Welcome to the extra day in the Gregorian Calendar's leap year 2008! To celebrate, consider this grid of lunar eclipse pictures - starting in leap year 1996 and ending with February's eclipse - with the date in numerical year/month/day format beneath each image. Mostly based on visibility from a site in Turkey, the 3x4 matrix includes 11 of the 13 total lunar eclipses during that period, and fills out the grid with the partial lunar eclipse of September 2006. Still, as the pictures are at the same scale, they illustrate a noticeable variation in the apparent size of the eclipsed Moon caused by the real change in Earth-Moon distance around the Moon's elliptical orbit. The total phases are also seen to differ in color and darkness. Those effects are due to changes in cloud cover and dust content in the atmosphere reddening and refracting sunlight into Earth's shadow. Of course, the next chance to add a total lunar eclipse to this grid will come at the very end of the decade.

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Comet SWAN Brightens

Explanation: A newly discovered comet has brightened enough to be visible this week with binoculars. The picturesque comet is already becoming a favored target for northern sky imagers. Pictured above just last week, Comet SWAN showed a bright blue-green coma and an impressive tail. Comet C/2006 M4 (SWAN) was discovered in June in public images from the Solar Wind Anisotropies (SWAN) instrument of NASA and ESA's Sun-orbiting SOHO spacecraft. Comet SWAN, near magnitude six, will be visible with binoculars in the northeastern sky not far from the Big Dipper over the next few days before dawn. The comet is expected to reach its peak brightness this week. Passing its closest to the Sun two days ago, Comet SWAN and will be at its closest to the Earth toward the end of this month. Comet SWAN's unusual orbit appears to be hyperbolic, meaning that it will likely go off into interstellar space, never to return.

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Light from the Heart Nebula

Explanation: What powers the Heart Nebula? The large emission nebula dubbed IC 1805 looks, in whole, like a human heart. The nebula glows brightly in red light emitted by its most prominent element: hydrogen. The red glow and the larger shape are all created by a small group of stars near the nebula's center. A close up spanning about 30 light years contains many of these stars is shown above . This open cluster of stars contains a few bright stars nearly 50 times the mass of our Sun, many dim stars only a fraction of the mass of our Sun, and an absent microquasar that was expelled millions of years ago. The Heart Nebula is located about 7,500 light years away toward the constellation of Cassiopeia.

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NGC 5905 and 5908

Explanation: These two beautiful galaxies, NGC 5905 (left) and NGC 5908 lie about 140 million light-years distant in the northern constellation Draco. Separated by about 500,000 light-years, the pair are actually both spiral galaxies and nicely illustrate the striking contrasts in appearance possible when viewing spirals from different perspectives. Seen face-on, NGC 5905 is clearly a spiral galaxy with bright star clusters tracing arms that wind outward from a prominent central bar. Oriented edge-on to our view, the spiral nature of NGC 5908 is revealed by a bright nucleus and dark band of obscuring dust characteristic of a spiral galaxy's disk. In fact, NGC 5908 is similar in appearance to the well studied edge-on spiral galaxy M104 - The Sombrero Galaxy.

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RCW 86: Historical Supernova Remnant

Explanation: In 185 AD, Chinese astronomers recorded the appearance of a new star in the Nanmen asterism - a part of the sky identified with Alpha and Beta Centauri on modern star charts. The new star was visible for months and is thought to be the earliest recorded supernova. Data from two orbiting X-ray telescopes of the 21st century, XMM-Newton and Chandra, now offer evidence that supernova remnant RCW 86 is indeed the debris from that stellar explosion. Their composite, false-color view of RCW 86 shows the expanding shell of material glowing in x-rays with high, medium, and low energies shown in blue, green, and red hues. Shock velocities measured in the x-ray emitting shell and an estimated radius of about 50 light-years can be used to find the apparent age of the remnant. The results indicate that light from the initial explosion could well have first reached planet Earth in 185 AD. Near the plane of our Milky Way Galaxy, RCW 86 is about 8,200 light-years away.

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NGC 1499: The California Nebula

Explanation: What's California doing in space? Drifting through the Orion Arm of the spiral Milky Way Galaxy, this cosmic cloud by chance echoes the outline of California on the west coast of the United States. Our own Sun also lies within the Milky Way's Orion Arm, only about 1,500 light-years from the California Nebula. Also known as NGC 1499, the classic emission nebula is around 100 light-years long. It glows with the red light characteristic of hydrogen atoms recombining with long lost electrons, stripped away (ionized) by energetic starlight. In this case, the star most likely providing the energetic starlight is the bright, hot, bluish Xi Persei, just right of the nebula and above picture center. Fittingly, this composite picture was made with images from a telescope in California - the 48-inch (1.2-meter) Samuel Oschin Telescope - taken as a part of the second National Geographic Palomar Observatory Sky Survey.

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Central IC 1805

Explanation: Cosmic clouds seem to form fantastic shapes in the central regions of emission nebula IC 1805. Of course, the clouds are sculpted by stellar winds and radiation from massive hot stars in the nebula's newborn star cluster (aka Melotte 15). About 1.5 million years young, the cluster stars appear in this colorful skyscape, along with dark dust clouds silhouetted against glowing atomic gas. A composite of narrow band telescopic images, the view spans about 15 light-years and shows emission from hydrogen in green, sulfur in red, and oxygen in blue hues. Wider field images reveal that IC 1805's simpler, overall outline suggests its popular name - The Heart Nebula. IC 1805 is located about 7,500 light years away toward the constellation Cassiopeia.

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Sharp Silhouette

Explanation: Though it's 93 million miles away, the Sun still hurts your eyes when you look at it. But bright sunlight (along with accurate planning and proper equipment!) resulted in this sharp silhouette of spaceship and space station. The amazing telescopic view, recorded on September 17, captures shuttle orbiter Atlantis and the International Space Station in orbit over planet Earth. At a range of 550 kilometers from the observing site near Mamers, Normandy, France, Atlantis (left) has just undocked and moved about 200 meters away from the space station. Tomorrow, yet another satellite of planet Earth can be seen in silhouette - the Moon will eclipse the Sun. This last eclipse of 2006 will be seen as an annular solar eclipse along a track that crosses northern South America and the south Atlantic.

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Eris: The Largest Known Dwarf Planet

Explanation: Is Pluto the largest dwarf planet? No! Currently, the largest known dwarf planet is (136199) Eris, renamed last week from 2003 UB313. Eris is just slightly larger than Pluto, but orbits as far as twice Pluto's distance from the Sun. Eris is shown above in an image taken by a 10-meter Keck Telescope from Hawaii, USA. Like Pluto, Eris has a moon, which has been officially named by the International Astronomical Union as (136199) Eris I (Dysnomia). Dysnomia is visible above just to the right of Eris. Dwarf planets Pluto and Eris are trans-Neptunian objects that orbit in the Kuiper belt of objects past Neptune. Eris was discovered in 2003, and is likely composed of frozen water-ice and methane. Since Pluto's recent demotion by the IAU from planet to dwarf planet status, Pluto has recently also been given a new numeric designation: (134340) Pluto. Currently, the only other officially designated "dwarf planet" is (1) Ceres.