Nebulae
Most pics courtesy of NASA
The Trifid Nebula from AAO
Explanation: Unspeakable beauty and unimaginable bedlam can be found together in the Trifid Nebula. Also known as M20, this photogenic nebula is visible with good binoculars towards the constellation of Sagittarius. The energetic processes of star formation create not only the colors but the chaos. The red-glowing gas results from high-energy starlight striking interstellar hydrogen gas. The dark dust filaments that lace M20 were created in the atmospheres of cool giant stars and in the debris from supernovae explosions. Which bright young stars light up the blue reflection nebula is still being investigated. The light from M20 we see today left perhaps 3000 years ago, although the exact distance remains unknown. Light takes about 50 years to cross M20.
Explanation: In the depths of the dark clouds of dust and molecular gas known as the Omega Nebula, stars continue to form. The above image from the Hubble Space Telescope's newly installed Advanced Camera for Surveys shows unprecedented detail in the famous star-forming region. The dark dust filaments that lace the center of Omega Nebula were created in the atmospheres of cool giant stars and in the debris from supernova explosions. The red and blue hues arise from glowing gas heated by the radiation of massive nearby stars. The points of light are the young stars themselves, some brighter than 100 Suns. Dark globules mark even younger systems, clouds of gas and dust just now condensing to form stars and planets. The Omega Nebula lies about 5000 light years away toward the constellation of Sagittarius. The region shown spans about 3000 times the diameter of our Solar System.
Explanation: Cones, pillars, and majestic flowing shapes abound in stellar nurseries where natal clouds of gas and dust are buffeted by energetic winds from newborn stars. A well-known example, the Cone Nebula within the bright galactic star-forming region NGC 2264, was captured in this close-up view from the Hubble Space Telescope's newest camera. While the Cone Nebula, about 2,500 light-years away in Monoceros, is around 7 light-years long, the region pictured here surrounding the cone's blunted head is a mere 2.5 light-years across. In our neck of the galaxy that distance is just over half way from the Sun to its nearest stellar neighbor, Alpha Centauri. The massive star NGC 2264 IRS, seen by Hubble's infrared camera in 1997, is the likely source of the wind sculpting the Cone Nebula and lies off the top of the image. The Cone Nebula's reddish veil is produced by glowing hydrogen gas.
Explanation: Why is N44C glowing so strangely? The star that appears to power the nebula, although young and bright, does not seem hot enough to create some of the colors observed. A search for a hidden hotter star in X-rays has come up empty. One hypothesis is that the known central star has a neutron star companion in a very wide orbit. Hot X-rays might only then be emitted during brief periods when the neutron star nears the known star and crashes through a disk of surrounding gas. Future observations might tell. N44C, pictured in the above Hubble Space Telescope image, is an emission nebula in the Large Magellanic Cloud, a neighboring galaxy to our Milky Way Galaxy. Flowing filaments of colorful gas and dark dust far from the brightest region are likely part of the greater N44 complex. It would take light about 125 years to cross N44C.
Explanation: To the east of the Lagoon Nebula is a star field rich in diversity. On the lower left are clouds rich in dark dust that hide background stars and young star systems still forming. Dark clouds include LDN 227 on the left and IC 1275 on the right, with a bright star near its tip. On the upper right are clouds rich in hot glowing gas, including part of the emission nebula NGC 6559 reflecting light from a group of massive blue stars. The NGC 6559 complex pictured above spans about 3 light years and likely has a common history with the Lagoon Nebula. The complex lies about 5000 light-years away toward the constellation of Sagittarius.
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 color photograph along with other nebulosities as part of the giant Orion Molecular Cloud complex, itself hundreds of light-years across. The magnificent Orion Nebula (aka M42) lies at the bottom of the image. This emission nebula's bright central regions were captured on fast film in a relatively short 30-second exposure. Above M42 are a cluster of prominent bluish reflection nebulae and fainter reddish emission nebulae recorded in additional exposures lasting up to 40 minutes. The Horsehead appears as a dark nebula, a small silhouette notched against the long red glow at the upper left. Alnitak is the easternmost star in Orion's belt and is seen as the brightest star above the Horsehead. Immediately to Alnitak's left is the Flame Nebula, with clouds of bright emission and dramatic dark dust lanes. The telescopic exposures were made from a site in the Southern French Alps at an altitude of 2,800 meters (a little closer to the stars!) in September of 2001.
Explanation: A photogenic group of nebulae can be found toward Chamaeleon, a constellation visible predominantly in skies south of the Earth's equator. Celestial objects visible there include the blue reflection nebulas highlighted by thin dust surrounding the bright stars in the above image center. Toward the top and lower right, dark molecular clouds laced with thick dust block light from stars in the background. The parent molecular cloud Chamaeleon I is located about 450 light years from Earth.
Explanation: How can a round star make a square nebula? This conundrum comes to light when studying planetary nebulae like IC 4406. Evidence indicates that IC 4406 is likely a hollow cylinder, with its square appearance the result of our vantage point in viewing the cylinder from the side. Were IC 4406 viewed from the top, it would likely look similar to the Ring Nebula. This representative-color picture is a composite made by combining images taken by the Hubble Space Telescope last June and this January. Hot gas flows out the ends of the cylinder, while filaments of dark dust and molecular gas lace the bounding walls. The star primarily responsible for this interstellar sculpture can be found in the planetary nebula's center. In a few million years, the only thing left visible in IC 4406 will be a fading white dwarf star.
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