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Planetary Nebulae

Most pics courtesy of NASA

The stars in Orion's belt line up with the pyramids in Egypt.

Aurora Borealis...04/07/00

Celebrating Hubble With NGC 6751

Credit:  A. Hajian (USNO) et al., Hubble Heritage Team (STScI/ AURA), NASA

          Explanation:  Planetary Nebulae do look simple, round, and planet-like in small telescopes.  But images from the orbiting Hubble Space Telescope have become well-known for showing these fluorescent gas shrouds of dying Sun-like stars to possess a staggering variety of detailed symmetries and shapes.  This composite color Hubble image of NGC 6751 is a beautiful example of a classic planetary nebula with complex features and was selected to commemorate the tenth anniversary of Hubble in orbit.  The colors were chosen to represent the relative temperature of the gas - blue, orange, and red indicating the hottest to coolest gas.  Winds and radiation from the intensely hot central star (140,000 degrees Celsius) have apparently created the nebula's streamer-like features.  The nebula's actual diameter is approximately 0.8 light-years or about 600 times the size of our solar system.  NGC 6751 is 6,500 light years distant in the constellation Aquila.

NGC 2264:  Stars, Dust, and Gas

Credit & Copyright:  Michael Bessell (RSAA, ANU), MSO

          Explanation:  The nebula surrounding bright star S Mon is filled with dark dust and glowing gas.  The strange shapes that haunt this star forming region originate from fine interstellar dust reacting in complex ways to the energetic light and hot gas being expelled by the young stars.  The above picture, in representative color, isolates the northern part of a greater nebula designated NGC 2264, which lies about 2500 light-years away and includes the Cone Nebula.  The blue glow directly surrounding S Mon results from reflection, where neighboring dust reflects light from the bright star.  The more diffuse red glow results from emission, where starlight ionizes hydrogen gas.  Pink areas are lit by a combination of the two processes.  A small group of stars surrounds S Mon, the brightest star in the picture and a star visible with the naked eye toward the constellation of Monocerus.

Eagle EGGs in M16

Credit: J. Hester & P. Scowen (ASU), HST, NASA

          Explanation:  Star forming regions known as "EGGs" are uncovered at the end of this giant pillar of gas and dust in the Eagle Nebula (M16).  EGGs, short for evaporating gaseous globules, are dense regions of mostly molecular hydrogen gas that fragment and gravitationally collapse to form stars.  Light from the hottest and brightest of these new stars heats the end of the pillar and causes further evaporation of gas - revealing yet more EGGs and more young stars.  This picture was taken by the Wide Field and Planetary Camera on board the Hubble Space Telescope.


M20:  The Trifid Nebula

Credit & Copyright:  Todd Boroson, AURA, NOAO, NSF

          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.

The Milky Way Near the Southern Cross

Credit & Copyright:  Greg Bock, Southern Astronomical Society

          Explanation:  This breathtaking patch of sky would be above you were you to stand at the South Pole of the Earth.  Just above and to the right of this photograph's center are the four stars that mark the boundaries of the famous Southern Cross.  At the top of this constellation, also known as The Crux, is the orange star Gamma Crucis.  The band of stars, dust, and gas crossing the middle of the photograph is part our Milky Way Galaxy.  In the very center of the photograph is the dark Coal Sack Nebula, and the bright nebula on the far right is the Carina Nebula.  The Southern Cross is such a famous constellation that it is depicted on the national flag of Australia.

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