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The Eskimo Nebula from the N
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| Title |
The Eskimo Nebula from the Newly Fixed Hubble |
| Explanation |
In 1787, astronomer William Herschel [ http://www.windows.umich.edu/cgi-bin/tour_def/people/enlightenment/herschel.html ] discovered the Eskimo Nebula [ http://www.seds.org/billa/twn/n2392x.html ]. From the ground, NGC 2392 resembles a person's head surrounded by a parka [ http://www.oregonlink.com/arctic/cormorant_parka.html ] hood. In 2000, just after being fixed [ http://antwrp.gsfc.nasa.gov/apod/ap000105.html ], the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap970306.html ] imaged the Eskimo Nebula. From space, the nebula displays gas clouds so complex they are not fully understood. The Eskimo Nebula [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1990ApJ...362..226O ] is clearly a planetary nebula [ http://antwrp.gsfc.nasa.gov/apod/planetary_nebulae.html ], and the gas seen above composed the outer layers of a Sun-like star only 10,000 years ago. The inner filaments visible above [ http://oposite.stsci.edu/pubinfo/pr/2000/07/pr-photos.html ] are being ejected by strong wind [ http://www-istp.gsfc.nasa.gov/Education/wsolwind.html ] of particles from the central star. The outer disk contains unusual light-year long orange filaments. The Eskimo Nebula lies about 5000 light-year [ http://www.treasure-troves.com/astro/Light-Year.html ]s away and is visible with a small telescope in the constellation [ http://www.emufarm.org/~cmbell/myth/myth.html ] of Gemini [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Gemini.html ]. |
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NGC 7635: The Bubble Nebula
| Title |
NGC 7635: The Bubble Nebula |
| Explanation |
What created this huge space bubble? A massive star [ http://antwrp.gsfc.nasa.gov/apod/ap971008.html ] that is not only bright and blue, but also emitting a fast stellar wind [ http://www-spof.gsfc.nasa.gov/Education/wsolwind.html ] of ionized gas [ http://www.unm.edu/~sgoold/Plasma.html ]. The Bubble Nebula [ http://heritage.stsci.edu/public/Oct22/bubble/NGC7635table.html ] is actually the smallest of three bubbles surrounding massive star BD+602522, and part of gigantic bubble network S162 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995A%26A...295..509C ] created with the help of other massive stars. As fast moving gas expands off BD+602522, it pushes surrounding sparse gas into a shell [ http://antwrp.gsfc.nasa.gov/apod/ap990626.html ]. The energetic starlight then ionizes the shell, causing it to glow. The above picture [ http://oposite.stsci.edu/pubinfo/pr/2000/04/index.html ] taken with the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap970306.html ] and released [ http://oposite.stsci.edu/pubinfo/pr/2000/04/content/prc0004.txt ] last week shows many details of the Bubble Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap981118.html ] never seen before and many still not understood. The nebula, also known as NGC 7635 [ http://www.aao.gov.au/AAO/local/www/dfm/int010.html ], is about six light-years across and visible with a small telescope towards the constellation of Cassiopeia [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Cassiopeia.html ]. |
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The Rosette Nebula in Hydrog
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| Title |
The Rosette Nebula in Hydrogen, Oxygen, and Sulfur |
| Explanation |
The Rosette Nebula is a large emission nebula [ http://seds.lpl.arizona.edu/billa/twn/types.html#emission ] located 3000 light-years away. The great abundance of hydrogen gas [ http://casswww.ucsd.edu/public/tutorial/Planck.html#atoms ] gives NGC 2237 [ http://seds.lpl.arizona.edu/billa/twn/n2237x.html ] its red color in most photographs [ http://antwrp.gsfc.nasa.gov/apod/ap980214.html ]. The wind [ http://antwrp.gsfc.nasa.gov/apod/ap990208.html ] from the open cluster [ http://antwrp.gsfc.nasa.gov/apod/ap980329.html ] of stars known as NGC 2244 has cleared a hole in the nebula's center. The above photograph [ http://www.noao.edu/image_gallery/html/im0557.html ], however, was taken in the light emitted by three elements of the gas ionized by the energetic central stars. Here green light originating from oxygen [ http://pearl1.lanl.gov/periodic/elements/8.html ] and blue light originating from sulfur [ http://pearl1.lanl.gov/periodic/elements/16.html ] supplements the red from hydrogen. Filaments of dark dust [ http://galileo.mpi-hd.mpg.de/ ] lace run through the nebula's gases. The origin of recently observed fast-moving molecular knots [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998A%26A...334..264C ] in the Rosette Nebula remains under investigation. |
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Eta and Keyhole in the Carin
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| Title |
Eta and Keyhole in the Carina Nebula |
| Explanation |
South is toward the top in this colorful close-up [ http://www.southern-astro.com.au/gallery.php?PhotoID=13 ] view of the Great Carina Nebula [ http://www.seds.org/Messier/xtra/ngc/n3372.html ] (NGC 3372), famous star-forming region of the southern sky. Covering an area surrounding the dusty Keyhole Nebula [ http://heritage.stsci.edu/2000/06/index.html ] (NGC 3324) near picture center, the image spans about 40 light-years within the larger Carina Nebula [ http://etacar.umn.edu/etainfo/images/index.html#wide ] at an estimated distance of 7,500 light-years. Like the more northerly Orion Nebula, the bright Carina Nebula [ http://www.noao.edu/image_gallery/html/im0667.html ] is easily visible to the naked-eye. But the dramatic colors in this telescopic picture are mapped colors [ http://hubblesite.org/sci.d.tech/ behind_the_pictures/meaning_of_color/eagle.shtml ], based on three exposures through narrow filters each intended to record the light emitted by specific atoms in the gaseous nebula. Sulfur is shown in blue, hydrogen in green and oxygen in red hues. The Carina Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap051015.html ] is home to young, extremely massive stars, including the still enigmatic [ http://arxiv.org/abs/astro-ph/0603168 ] variable Eta Carinae [ http://www.seds.org/messier/xtra/ngc/etacar.html ], a star with well over 100 times the mass of the Sun. Highlighted by diffraction [ http://antwrp.gsfc.nasa.gov/apod/ap010415.html ] spikes, Eta is just above [ http://etacar.umn.edu/etainfo/basic/ ] and right (east) of the Keyhole. |
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NGC 1999: Reflection Nebula
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| Title |
NGC 1999: Reflection Nebula in Orion |
| Explanation |
A dusty bright nebula [ http://home.wxs.nl/~geldo006/brigneb.html ] contrasts dramatically with a dusty dark nebula in this Hubble Space Telescope image [ http://oposite.stsci.edu/pubinfo/pr/2000/10/index.html ] recorded shortly after December's orbital servicing mission [ http://hubble.gsfc.nasa.gov/ ]. The nebula [ http://oposite.stsci.edu/pubinfo/pr/2000/10/faq.html ], cataloged as NGC [ http://antwrp.gsfc.nasa.gov/apod/ap990429.html ] 1999, is a reflection nebula [ http://antwrp.gsfc.nasa.gov/apod/reflection_nebulae.html ], which shines by reflecting light from a nearby star. Unlike emission nebulae [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ], whose reddish glow [ http://antwrp.gsfc.nasa.gov/apod/ap980828.html ] comes from excited atoms of gas, reflection nebulae have a bluish cast [ http://www.physics.muni.cz/~ondra/mix/mix.html ] as their interstellar dust grains [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ] preferentially reflect blue starlight. While perhaps the most famous reflection nebulae surround the bright young stars of the Pleiades [ http://antwrp.gsfc.nasa.gov/apod/ap000227.html ] star cluster, NGC 1999's stellar illumination is provided by the embedded variable star V380 [ http://donald.phast.umass.edu/research/comap/V380sm.html ] Orionis, seen here just left of center. Extending right of center, the ominous [ http://antwrp.gsfc.nasa.gov/apod/ap990226.html ] dark nebula [ http://antwrp.gsfc.nasa.gov/apod/dark_nebulae.html ] is actually a condensation of cold molecular gas and dust so thick and dense that it blocks light. From our perspective it lies in front of the bright nebula, silhouetted against the ghostly nebular glow. New stars [ http://dsnra.jpl.nasa.gov/origins/nyt.html ] will likely form within the dark cloud, called a Bok globule [ http://antwrp.gsfc.nasa.gov/apod/ap961229.html ], as self-gravity continues to compress its dense gas and dust. Reflection nebula NGC 1999 [ http://heritage.stsci.edu/public/ 2000mar2/ngc1999table.html ] lies about 1500 light-years away in the constellation Orion [ http://www.seds.org/messier/more/oricloud.html ], just south of Orion's well known emission nebula, M42 [ http://antwrp.gsfc.nasa.gov/apod/ap990522.html ]. |
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Barnard's Loop around the Ho
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| Title |
Barnard's Loop around the Horsehead Nebula |
| Explanation |
Why is the Horsehead Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap030713.html ] surrounded by a bubble? Although glowing like an emission nebula [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ], the origin of the bubble [ http://antwrp.gsfc.nasa.gov/apod/ap050420.html ], known as Barnard's Loop [ http://weblore.com/richard/barnard's_loop.htm ], is currently unknown. Progenitor hypotheses include the wind [ http://www-spof.gsfc.nasa.gov/Education/wsolwind.html ]s from bright Orion stars and the supernovas [ http://heasarc.gsfc.nasa.gov/docs/snr.html ] of stars long gone. Barnard's Loop [ http://www.seds.org/messier/xtra/ngc/b-loop.html ] is too faint to be identified with the unaided eye. The nebula [ http://en.wikipedia.org/wiki/Barnard%27s_Loop ] was discovered only in 1895 by E. E. Barnard [ http://astro.uchicago.edu/yerkes/virtualmuseum/Barnardfull.html ] on long duration film exposures. The above image was taken in a single specific color [ http://en.wikipedia.org/wiki/Hydrogen_alpha ] emitted by hydrogen [ http://periodic.lanl.gov/elements/1.html ] to bring out detail. To the left of the Horsehead Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap040115.html ], visible as the small dark indentation near the image top, is the photogenic Flame Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap990713.html ]. |
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The Pipe Dark Nebula
| Title |
The Pipe Dark Nebula |
| Explanation |
The dark nebula predominant at the lower left of the above photograph is known as the Pipe Nebula. The dark clouds, suggestively shaped like smoke rising from a pipe, are caused by absorption of background starlight by dust [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#dust ]. These dust clouds can be traced all the way to the Rho Ophiuchi nebular clouds [ http://antwrp.gsfc.nasa.gov/apod/ap970922.html ] on the right. The brightest star in the field is Antares [ http://antwrp.gsfc.nasa.gov/apod/ap980726.html ]. Many types of nebula are highlighted here: the red are emission nebula [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ], the blue are reflection nebula [ http://antwrp.gsfc.nasa.gov/apod/reflection_nebulae.html ], and the dark are absorption nebula [ http://antwrp.gsfc.nasa.gov/apod/dark_nebulae.html ]. This picture has been digitally enhanced [ http://www.astropix.com/HTML/J_DIGIT/ETHICS.HTM ]. |
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Comet Meets Ring Nebula: Par
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| Title |
Comet Meets Ring Nebula: Part II |
| Explanation |
Moving rapidly through planet Earth's night sky, Fragment C of crumbling [ http://www.spitzer.caltech.edu/Media/releases/ ssc2006-13/index.shtml ] comet 73P/Schwassmann-Wachmann 3 [ http://skyandtelescope.com/observing/objects/comets/ article_1704_1.asp ] passed almost directly in front of M57 [ http://seds.lpl.arizona.edu/messier/m/m057.html ] - the Ring Nebula, and faint spiral galaxy IC 1296 [ http://www.skyhound.com/sh/archive/jul/IC_1296.html ] on May 8. In fact, in this gorgeous view [ http://www.masil-astro-imaging.com/ Latest_Images.html ], the bright head of Fragment C is separated by only about 0.1 degrees from M57, with the tail apparently engulfing nebula and galaxy. Recorded from Elizabeth, Illinois, USA, this picture corresponds to the cosmic scene only 30 minutes after yesterday's picture [ http://antwrp.gsfc.nasa.gov/apod/ap060511.html ] of the approaching alignment. The relative motion of the comet [ http://www.galacticimages.com/astronomical_events.html ] against the background stars and nebulae is easy to see when comparing the two images. This comet's fragments [ http://www.skyhound.com/sh/73P.html ] will be near their closest approach in the coming days, about 10 million kilometers away, and none pose any danger [ http://www.nasa.gov/mission_pages/hubble/ Comet_73P.html ] to our fair planet. |
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Comet Meets Ring Nebula: Par
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| Title |
Comet Meets Ring Nebula: Part I |
| Explanation |
As dawn approached on May 8, astronomer Stefan Seip carefully watched Fragment C of broken [ http://neo.jpl.nasa.gov/cgi-bin/db?name=73P ] comet 73P/Schwassmann-Wachmann 3 [ http://skyandtelescope.com/observing/objects/comets/ article_1704_1.asp ] approach M57 [ http://seds.lpl.arizona.edu/messier/m/m057.html ] - the Ring Nebula, and faint spiral galaxy IC 1296 [ http://www.skyhound.com/sh/archive/jul/IC_1296.html ]. Of course, even though the trio seemed to come close together in a truly cosmic photo opportunity, the comet [ http://antwrp.gsfc.nasa.gov/apod/ap060504.html ] is in the inner part of our solar system, a mere 0.5 light-minutes [ http://en.wikipedia.org/wiki/Light-minute ] or so from Seip's telescope located near Stuttgart, Germany, planet Earth [ http://science.nasa.gov/headlines/y2006/ 24mar_73p.htm?list237669 ]. The Ring Nebula (upper right) is more like 2,000 light-years distant, well within our own Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap050825.html ]. At a distance of 200 million light-years, IC 1296 (between comet and ring) is beyond even the Milky Way's boundaries. Because the comet is so close, it appears to move relatively rapidly against the distant stars. This dramatic telescopic view [ http://www.photomeeting.de/astromeeting/comets/ 060508SchwWas_a_d.htm ] was composited from two sets of images, one compensating [ http://www.ewellobservatory.com/ccd/ comet.cfm ] for the comet's apparent motion and one recording the background stars and nebulae [ http://antwrp.gsfc.nasa.gov/apod/ap030516.html ]. |
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M20: The Trifid Nebula
| Title |
M20: The Trifid Nebula |
| Explanation |
Unspeakable beauty and unimaginable bedlam can be found together in the Trifid Nebula [ http://www.seds.org/messier/m/m020.html ]. Also known as M20, this photogenic nebula [ http://www.noao.edu/image_gallery/html/im0587.html ] is visible with good binoculars towards the constellation [ http://www.astro.wisc.edu/~dolan/constellations/extra/constellations.html ] of Sagittarius [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Sagittarius.html ]. The energetic processes of star formation [ http://antwrp.gsfc.nasa.gov/apod/ap990502.html ] create not only the colors but the chaos. The red-glowing gas [ http://antwrp.gsfc.nasa.gov/apod/ap980828.html ] results from high-energy starlight striking interstellar hydrogen [ http://pearl1.lanl.gov/periodic/elements/1.html ] gas. The dark dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ] filaments [ http://antwrp.gsfc.nasa.gov/apod/ap990607.html ] that lace M20 [ http://antwrp.gsfc.nasa.gov/apod/ap970828.html ] were created in the atmospheres of cool giant stars [ http://www.astro.keele.ac.uk/workx/starlife/StarpageS_26M.html ] and in the debris [ http://antwrp.gsfc.nasa.gov/apod/ap990803.html ] from supernovae [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/supernovae.html ] explosions. Which bright young stars light up the blue reflection nebula [ http://antwrp.gsfc.nasa.gov/apod/reflection_nebulae.html ] is still being investigated [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1986AJ.....92.1125L ]. The light from M20 [ http://www.aao.gov.au/local/www/dfm/aat069.html ] we see today left perhaps 3000 years ago, although the exact distance remains unknown. Light takes about 50 years to cross M20 [ http://www.seds.org/billa/twn/n6514x.html ]. |
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The Gum Nebula
| Title |
The Gum Nebula |
| Explanation |
Named for Australian astronomer Colin Stanley Gum [ http://en.wikipedia.org/wiki/Colin_Stanley_Gum ] (1924-1960), The Gum Nebula [ http://www.southernskyphoto.com/southern_sky/gum_nebula.htm ] is so large and close it is actually hard to see. In fact [ http://antwrp.gsfc.nasa.gov/apod/ap020217.html ], we are only about 450 light-years from the front edge and 1,500 light-years from the back edge of this cosmic cloud of glowing hydrogen gas. Covered in this 41 degree-wide [ http://canopus.physik.uni-potsdam.de/~axm/ photo.cgi?Image=images/Vela_50mm_HaRGB_1000 ] mosaic of H-alpha [ http://antwrp.gsfc.nasa.gov/apod/ap051223.html ] images, the faint emission region is otherwise easy to lose against the background of Milky Way stars. The complex [ http://adsabs.harvard.edu/cgi-bin/ nph-bib_query?bibcode=1993A%26A...280..231S ] nebula is thought to be a supernova remnant [ http://chandra.harvard.edu/xray_sources/ supernovas.html ] over a million years old, sprawling across [ http://hawastsoc.org/deepsky/car/index.html#Myth ] the southern constellations Vela and Puppis. Sliding your cursor over this spectacular wide field view will reveal the location of objects embedded in The Gum Nebula, including the Vela supernova remnant [ http://www.aao.gov.au/images/captions/ uks002.html ]. |
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IC 4406: A Seemingly Square
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| Title |
IC 4406: A Seemingly Square Nebula |
| Explanation |
How can a round star make a square nebula? This conundrum came to light with the discovery of planetary nebulae [ http://zebu.uoregon.edu/~imamura/208/feb22/feb22.html ] like IC 4406. IC 4406 [ http://www.astro.psu.edu/users/rbc/IC4406.html ] is most probably cylindrical, with its square appearance the result of our vantage point in viewing the cylinder. Hot gas is known [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1991A%26A...251..560S ] to be flowing out the ends of the cylinder, while filaments of dark dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ] and molecular gas [ http://antwrp.gsfc.nasa.gov/apod/ap970430.html ] lace the bounding walls. The star primarily responsible for this interstellar sculpture [ http://oposite.stsci.edu/pubinfo/pr/97/pn/ ] can be found in the planetary nebula's center. In a few million years, the only thing left visible in IC 4406 [ http://www.iras.ucalgary.ca/cgi-bin/zhang/webpn?IC4406 ] will be a fading white dwarf star [ http://antwrp.gsfc.nasa.gov/apod/ap971102.html ]. |
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NGC 6164: A Bipolar Emission
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| Title |
NGC 6164: A Bipolar Emission Nebula |
| Explanation |
How did a star form this beautiful nebula? In the middle of emission nebula [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ] NGC 6164-5 is an unusually massive star nearing the end of its life. The star, visible in the center of the above image [ http://www.gemini.edu/dualneb ] and catalogued as HD 148937, is so hot that the ultraviolet light [ http://imagers.gsfc.nasa.gov/ems/uv.html ] it emits heats up gas that surrounds it. That gas was likely thrown off from the star, possibly by its fast rotation, like a rotating lawn sprinkler. Expelled material might have been further channeled by the magnetic field [ http://antwrp.gsfc.nasa.gov/apod/ap980629.html ] of the star, creating the symmetric shape [ http://antwrp.gsfc.nasa.gov/apod/ap060326.html ] of the bipolar nebula [ http://antwrp.gsfc.nasa.gov/apod/ap030113.html ]. Several cometary knots [ http://antwrp.gsfc.nasa.gov/apod/ap960416.html ] of gas are also visible on the lower left. NGC 6164-5 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1985PASP...97..780F&] spans about four light years [ http://en.wikipedia.org/wiki/Light_years ] and is located about 4,000 light years away toward the southern constellation Norma [ http://www.seds.org/Maps/Stars_en/Fig/norma.html ]. |
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The Eskimo Nebula from Hubbl
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| Title |
The Eskimo Nebula from Hubble |
| Explanation |
In 1787, astronomer William Herschel [ http://www.windows.ucar.edu/cgi-bin/tour_def/people/enlightenment/herschel.html ] discovered the Eskimo Nebula [ http://www.seds.org/billa/twn/n2392x.html ]. From the ground, NGC 2392 resembles a person's head surrounded by a parka [ http://www.oregonlink.com/arctic/cormorant_parka.html ] hood. In 2000, the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap021124.html ] imaged the Eskimo Nebula [ http://www.noao.edu/outreach/aop/observers/n2392.html ]. From space, the nebula displays gas clouds so complex they are not fully understood. The Eskimo Nebula [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1990ApJ...362..226O ] is clearly a planetary nebula [ http://antwrp.gsfc.nasa.gov/apod/planetary_nebulae.html ], and the gas seen above composed the outer layers of a Sun [ http://antwrp.gsfc.nasa.gov/apod/sun.html ]-like star only 10,000 years ago. The inner filaments visible above [ http://hubblesite.org/newscenter/newsdesk/archive/releases/2000/07/image/a ] are being ejected by strong wind [ http://www-istp.gsfc.nasa.gov/Education/wsolwind.html ] of particles from the central star. The outer disk contains unusual light-year [ http://en.wikipedia.org/wiki/Light_year ] long orange filaments. |
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The North America Nebula
| Title |
The North America Nebula |
| Explanation |
Here's a familiar shape in an unfamiliar location! This emission nebula [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ] is famous partly because it resembles Earth's continent of North America. To the right of the North America Nebula [ http://www.seds.org/messier/xtra/ngc/n7000.html ], cataloged as NGC 7000 [ http://aspsky.org/ngc/ngc_6-7k.html ], is a less luminous Pelican Nebula [ http://voltaire.csun.edu/pelican.html ]. The two emission nebula [ http://www.seds.org/messier/nebula.html ] measure about 50 light-years across, are located about 1500 light-years [ http://www.treasure-troves.com/astro/Light-Year.html ] away, and are separated by a dark absorption [ http://antwrp.gsfc.nasa.gov/apod/dark_nebulae.html ] cloud. The nebulae can be seen with binoculars from a dark location. Look for a small nebular patch [ http://antwrp.gsfc.nasa.gov/apod/ap971009.html ] north-east of bright star Deneb [ http://www.astro.wisc.edu/~dolan/constellations/hr/7924.html ] in the constellation of Cygnus [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Cygnus.html ]. It is still unknown which star or stars ionize the red-glowing hydrogen [ http://pearl1.lanl.gov/periodic/elements/1.html ] gas. |
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Reflection Nebula M78
| Title |
Reflection Nebula M78 |
| Explanation |
An eerie blue glow and ominous columns of dark dust highlight M78, a bright reflection nebula [ http://antwrp.gsfc.nasa.gov/apod/reflection_nebulae.html ] in the constellation of Orion [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Orion.html ]. The dust [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#dust ] not only absorbs light, but also reflects the light of several bright blue stars that formed recently [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1975ApJ...196..489S ] in the nebula. The same type of scattering that colors the daytime sky [ http://math.ucr.edu/home/baez/physics/blue_sky.html ] further enhances the blue color. M78 [ http://www.seds.org/messier/m/m078.html ] is about five light-years [ http://www.glyphweb.com/esky/concepts/lightyear.html ] across and visible through a small telescope. M78 appears above [ http://www.sdss.org/gallery/gal_data.html ] only as it was 1600 years ago, however, because that is how long it takes light to go from there [ http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?1975ApJ...195L..23B ] to here. M78 [ http://www.airdigital.com/M78.html ] belongs to the larger Orion Molecular Cloud Complex [ http://antwrp.gsfc.nasa.gov/apod/ap971201.html ] that contains the Great Nebula in Orion [ http://antwrp.gsfc.nasa.gov/apod/ap980127.html ] and the Horsehead Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap990519.html ]. |
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Horse Head Shaped Reflection
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| Title |
Horse Head Shaped Reflection Nebula IC 4592 |
| Explanation |
Do you see the horse's head? What you are seeing is not the famous Horsehead nebula [ http://antwrp.gsfc.nasa.gov/apod/ap051130.html ] toward Orion but rather a fainter nebula that only takes on a familiar form with deeper imaging. The main part of the above imaged [ http://www.robgendlerastropics.com/IC4592JM.html ] molecular cloud [ http://antwrp.gsfc.nasa.gov/apod/ap060409.html ] complex is a reflection nebula [ http://en.wikipedia.org/wiki/Reflection_nebula ] cataloged as IC 4592 [ http://aisig.sdaa.org/astroblogDetail.asp?imgID=1035&UserID=66 ]. Reflection nebulas are actually made up of very fine dust [ http://antwrp.gsfc.nasa.gov/apod/ap030706.html ] 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 [ http://en.wikipedia.org/wiki/Nu_Scorpii ], one of the brighter star systems toward the constellation of Scorpius [ http://www.astro.uiuc.edu/~kaler/sow/sco-t.html ]. A second reflection nebula [ http://antwrp.gsfc.nasa.gov/apod/reflection_nebulae.html ] dubbed IC 4601 is visible surrounding two stars on the far right. |
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The Carina Nebula in Infrare
…
| Title |
The Carina Nebula in Infrared |
| Explanation |
About three million years ago, the stars in the Keyhole Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap990523.html ] began to form. The above picture [ http://www.ipac.caltech.edu/2mass/gallery/powarc.html ] of the Keyhole Nebula [ http://www.seds.org/nineplanets/twn/n3324x.html ], also known as the Carina Nebula or NGC 3372, shows in infrared light [ http://www.ipac.caltech.edu/Outreach/Edu/infrared.html ] many facets of this dramatic stellar nursery [ http://antwrp.gsfc.nasa.gov/apod/stellar_nurseries.html ] which lies only 9,000 light-years away. Fine dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ] reflects starlight while being heated and emitting light of its own. Open clusters [ http://antwrp.gsfc.nasa.gov/apod/open_clusters.html ] Trumpler 14 and Trumpler [ http://www.treasure-troves.com/bios/Trumpler.html ] 16 are visible in the lower left and upper right of the nebula. The bright star near Trumpler 14 [ http://www.aao.gov.au/images/captions/aat037.html ] is called Eta Carinae [ http://www.seds.org/billa/twn/n3372x.html ] and is one of the most unusual [ http://www.bris.ac.uk/Depts/Chemistry/MOTM/silly/sillymols.htm ] stars known. A candidate for a supernova [ http://msgc.engin.umich.edu/cgi-bin/tour.cgi?link=/the_universe/supernova.html ] in the next few thousand years, Eta Carinae [ http://antwrp.gsfc.nasa.gov/apod/ap980816.html ] faded from being one of the brightest stars in the sky during the 1800s. Despite intensive study [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000ApJ...530L.107D ], astronomers remain unsure whether Eta Carinae [ http://heasarc.gsfc.nasa.gov/docs/objects/heapow/archive/stars/etacar_pspc_19990525.html ] is part of a binary star [ http://antwrp.gsfc.nasa.gov/apod/ap970219.html ] system. |
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MyCn18: An Hourglass Nebula
| Title |
MyCn18: An Hourglass Nebula |
| Explanation |
The sands of time are running out for the central star of this hourglass-shaped planetary nebula [ http://fusedweb.pppl.gov/CPEP/ Chart_Pages/5.Plasmas/Nebula/Planetary.html ]. With its nuclear fuel [ http://fusedweb.pppl.gov/default.html ] exhausted, this brief, spectacular, closing phase of a Sun-like star's life [ http://observe.ivv.nasa.gov/nasa/space/stellardeath/stellardeath_contents.html ] occurs as its outer layers are ejected - its core becoming a cooling, fading White Dwarf [ http://antwrp.gsfc.nasa.gov/apod/ap971102.html ]. Astronomers have recently used the Hubble Space Telescope [ http://hubble.stsci.edu/ ] (HST) to make a series of images of planetary nebulae [ http://antwrp.gsfc.nasa.gov/apod/planetary_nebulae.html ], including the one above [ http://www.stsci.edu/pubinfo/PR/96/07.html ]. Here, delicate rings of colorful glowing gas (nitrogen-red, hydrogen-green, and oxygen-blue) outline the tenuous walls of the "hourglass". The unprecedented sharpness of the HST images has revealed surprising details [ http://www.stsci.edu/pubinfo/gif/Hourgls.txt ] of the nebula ejection process [ http://antwrp.gsfc.nasa.gov/apod/ap960117.html ] and may help resolve the outstanding mystery of the variety of complex shapes and symmetries of planetary nebulae [ http://www.astro.washington.edu/balick/WFPC2/index.html ]. |
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Shapley 1: An Annular Planet
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| Title |
Shapley 1: An Annular Planetary Nebula |
| Explanation |
What happens when a star runs out of nuclear fuel? The center condenses into a white dwarf [ http://antwrp.gsfc.nasa.gov/apod/ap971102.html ] while the outer atmospheric layers are expelled into space and appear as a planetary nebula. This particular planetary nebula, designated Shapley 1 [ http://www.aao.gov.au/images/captions/aat095.html ] after the famous astronomer Harlow Shapley, has a very apparent annular ring like structure. Although some of these nebulae appear like planets on the sky (hence their name), they actually surround stars far outside our Solar System. |
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Pelican Nebula Ionization Fr
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| Title |
Pelican Nebula Ionization Front |
| Explanation |
The Pelican Nebula is slowly being transformed. IC 5070, the official designation, is divided from the larger North America Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap000501.html ] by a molecular cloud [ http://antwrp.gsfc.nasa.gov/apod/ap990511.html ] filled with dark dust [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#dust ]. The Pelican [ http://www.usit.com/mccubbin/Pelican.html ], however, receives much study because it is a particularly active mix of star formation [ http://antwrp.gsfc.nasa.gov/apod/ap990502.html ] and evolving gas clouds. The above picture [ http://www.noao.edu/image_gallery/html/im0555.html ] was produced in two specific colors to better understand these interactions. Here, hot hydrogen [ http://chemlab.pc.maricopa.edu/periodic/h.html ] gas glows in red, while cooler Sulfur [ http://chemlab.pc.maricopa.edu/periodic/S.html ] glows blue-green. The light from young energetic stars is slowly transforming the cold gas to hot gas, with the advancing boundary [ http://antwrp.gsfc.nasa.gov/apod/ap981118.html ] between the two known as an ionization [ http://csep10.phys.utk.edu/astr162/lect/light/ionization.html ] front. Particularly dense filaments of cold gas are seen to still remain. Millions of years from now this nebula might no longer be known as the Pelican [ http://www.phillyzoo.org/pz0012.htm ], as the balance and placement of stars and gas [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1980ApJ...239..121B ] will leave something that appears completely different. |
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The Crab Nebula in Blue and
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| Title |
The Crab Nebula in Blue and White |
| Explanation |
The Crab Nebula is a complex shell of expanding gas. The Crab Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap991122.html ] formed from a star that was seen to explode in a supernova [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/supernovae.html ] about 1000 years ago. This two color composite image [ http://www.noao.edu/image_gallery/html/im0466.html ] taken with the WIYN 3.5-meter telescope [ http://www.noao.edu/wiyn/wiynis.html ] shows in great detail filamentary structure of the glowing hydrogen [ http://pearl1.lanl.gov/periodic/elements/1.html ] gas. Also known as M [ http://www.seds.org/messier/xtra/history/CMessier.html ]1, the center is home to a dense neutron star [ http://www.astro.umd.edu/~miller/nstar.html ], a star as massive as our Sun [ http://www.seds.org/nineplanets/nineplanets/sol.html ] but only the size of a city [ http://antwrp.gsfc.nasa.gov/apod/ap970408.html ]. The neutron star [ http://antwrp.gsfc.nasa.gov/apod/neutron_stars.html ] is a pulsar [ http://lheawww.gsfc.nasa.gov/users/padi/Pulse/crab.html ] that spins thirty times a second and spits out energy that powers the nebula. The nebula [ http://nineplanets.org/twn/n1952x.html ] is named from its likeness to a crab [ http://www.clever.net/kerry/creature/helmet.htm ] in an early drawing. The Crab Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap981122.html ] still presents mysteries [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995ApJ...454L.129F ] today as the total mass of the nebula and pulsar [ http://www.jb.man.ac.uk/~pulsar/Education/Sounds/sounds.html ] appears much less than the mass of the original pre-supernova star [ http://antwrp.gsfc.nasa.gov/apod/ap970812.html ]! |
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Light from the Heart Nebula
| Title |
Light from the Heart Nebula |
| Explanation |
What powers the Heart Nebula? The large emission nebula [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ] dubbed IC 1805 [ http://antwrp.gsfc.nasa.gov/apod/ap040917.html ] looks, in whole, like a human heart [ http://www.pbs.org/wgbh/nova/heart/heartmap.html ]. The nebula glows brightly in red light emitted by its most prominent element: hydrogen [ http://en.wikipedia.org/wiki/Hydrogen ]. The red glow and the larger shape are all created by a small group of stars near the nebula's center [ http://antwrp.gsfc.nasa.gov/apod/ap060922.html ]. A close up spanning about 30 light years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] contains many of these stars is shown above [ http://www.telescopes.cc/ic1805large.htm ] . This open cluster [ http://antwrp.gsfc.nasa.gov/apod/open_clusters.html ] of stars contains a few bright stars [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2006A%26A...456.1121D ] nearly 50 times the mass of our Sun, many dim stars only a fraction of the mass of our Sun, and an absent microquasar [ http://antwrp.gsfc.nasa.gov/apod/ap040916.html ] that was expelled millions of years ago. The Heart Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap031022.html ] is located about 7,500 light years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] away toward the constellation [ http://www.mallorcaweb.net/masm/descon1.htm ] of Cassiopeia [ http://www.seds.org/Maps/Stars_en/Fig/cassiopeia.html ]. |
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NGC 1499: The California Neb
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| Title |
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 [ http://www.anzwers.org/free/universe/nebulae/ ngc1499.html ] by chance echoes the outline of California [ http://en.wikipedia.org/wiki/California ] on the west coast of the United States [ https://www.cia.gov/cia/publications/factbook/geos/us.html ]. Our own Sun also lies within the Milky Way's Orion Arm [ http://www.anzwers.org/free/universe/5000lys.html ], only about 1,500 light-years from the California Nebula [ http://en.wikipedia.org/wiki/California_Nebula ]. Also known as NGC 1499 [ http://www.seds.org/~spider/spider/ Misc/n1499.html ], the classic emission nebula is around 100 light-year [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ]s long. It glows with the red light characteristic of hydrogen atoms recombining with long lost [ http://antwrp.gsfc.nasa.gov/apod/lib/lament.html ] electrons, stripped away (ionized [ http://csep10.phys.utk.edu/ astr162/lect/light/ionization.html ]) 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 [ http://www.astro.caltech.edu/~wsk/ngc1499.html ] picture was made with images from a telescope in California - the 48-inch (1.2-meter) Samuel Oschin Telescope [ http://www.astro.caltech.edu/~wsk/sot.html ] - taken as a part of the second National Geographic Palomar [ http://antwrp.gsfc.nasa.gov/apod/ap030807.html ] Observatory Sky Survey [ http://www.astro.caltech.edu/~wws/poss2.html ]. |
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At the Edge of the Crescent
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| Title |
At the Edge of the Crescent Nebula |
| Explanation |
The Crescent Nebula is a rapidly expanding shell of gas surrounding a dying star. In this recently released image [ http://oposite.stsci.edu/pubinfo/PR/2000/23/pr-photos.html ] by the Hubble Space Telescope [ http://oposite.stsci.edu/pubinfo/HSToverview.html ], a bright dynamic part of the nebula three light-years across is shown in representative color. The Crescent Nebula [ http://www.ne.jp/asahi/stellar/scenes/object_e/ngc6888.htm ] began to form about 250,000 years ago as central Wolf-Rayet [ http://antwrp.gsfc.nasa.gov/apod/ap970928.html ] star WR 136 began to shed its outer envelope in a strong stellar wind [ http://www-istp.gsfc.nasa.gov/Education/wsolwind.html ], expelling the equivalent of our Sun's mass every 10,000 years. This wind [ http://science.msfc.nasa.gov/ssl/pad/solar/sun_wind.htm ] has been impacting surrounding interstellar gas [ http://antwrp.gsfc.nasa.gov/apod/ap000412.html ], compacting it into a series of complex shells, and lighting it up. The Crescent Nebula [ http://www.astro.uni-bonn.de/~maltmann/n6888colinfo.html ], also known as NGC 6888, lies about 4,700 light-years [ http://www.howstuffworks.com/question94.htm ] away in the constellation [ http://www.eaglequest.net/~bondono/iconst.html ] of Cygnus [ http://www.seds.org/Maps/Stars_en/Fig/cygnus.html ] and can only be seen through a telescope. Star WR 136 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996A%26A...316..133G ] will probably undergo a supernova [ http://antwrp.gsfc.nasa.gov/apod/supernova_remnants.html ] explosion sometime in the next million years. |
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Star EGGs in the Eagle Nebul
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| Title |
Star EGGs in the Eagle Nebula |
| Explanation |
Where do stars form? One place, star forming regions known as "EGGs", are uncovered at the end of this giant pillar [ http://antwrp.gsfc.nasa.gov/apod/ap050424.html ] of gas and dust [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#dust ] in the Eagle Nebula [ http://en.wikipedia.org/wiki/Eagle_Nebula ] (M [ http://antwrp.gsfc.nasa.gov/apod/messier.html ]16). EGGs, short for evaporating gaseous globules [ http://antwrp.gsfc.nasa.gov/apod/ap030816.html ], are dense regions of mostly molecular hydrogen [ http://periodic.lanl.gov/elements/1.html ] gas that fragment and gravitationally collapse to form stars [ http://antwrp.gsfc.nasa.gov/apod/ap060403.html ]. Light from the hottest and brightest of these new stars [ http://antwrp.gsfc.nasa.gov/apod/ap060109.html ] heats the end of the pillar and causes further evaporation of gas - revealing yet more EGGs [ ftp://ftp.hq.nasa.gov/pub/pao/pressrel/1995/95-190.txt ] and more young stars. This picture [ http://hubblesite.org/newscenter/newsdesk/archive/releases/1995/44/image/b ] was taken by the Wide Field and Planetary Camera [ http://www.stsci.edu/instruments/wfpc2/wfpc2_top.html ] on board the Hubble Space Telescope [ http://www.stsci.edu/hst/HST_overview/ ]. |
|
Emerging Planetary Nebula CR
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| Title |
Emerging Planetary Nebula CRL 618 |
| Explanation |
CRL 618 may look to some like an Olympian [ http://www.olympics.com/ ] declaring victory. Only a few hundred years ago, however, CRL 618 [ http://hubble.esa.int/hubble/news/index.cfm?oid=24527 ] appeared as a relatively modest red giant star [ http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/971016.html ]. Since then it has run out of core material to fuse [ http://fusedweb.pppl.gov/CPEP/Chart.html ] and so has started to become a planetary nebula [ http://antwrp.gsfc.nasa.gov/apod/planetary_nebulae.html ]. In its current proto-planetary nebula [ http://www.astro.washington.edu/palen/Research/nsf/intro.html ] phase, CRL 618 [ http://hubble.esa.int/content/news/index.cfm?aid=18&cid=599&oid=12850 ] is evolving quickly, expelling hot gasses in complex jets [ http://antwrp.gsfc.nasa.gov/apod/ap960129.html ] and rings moving outwards faster than 700,000 kilometers per hour. In a few thousand years, the glowing core of the cool red giant [ http://www.historyoftheuniverse.com/starold.html ] will be bare, revealing a hot white dwarf star [ http://antwrp.gsfc.nasa.gov/apod/ap971102.html ]. Much remains unknown about planetary nebulae [ http://antwrp.gsfc.nasa.gov/apod/ap990321.html ] formation, including details of how geometries like this form. Perhaps one day some part of this nebula will be able to declare victory - CRL 618 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999ESASP.427..285C ] has an extraordinary abundance of carbon-chain molecules [ http://www.ifa.hawaii.edu/~wynnwill/110/16_life.htm ]. |
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NGC 6960: The Witch's Broom
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| Title |
NGC 6960: The Witch's Broom Nebula |
| Explanation |
Ten thousand years ago, before the dawn of recorded human history [ http://news.bbc.co.uk/hi/english/sci/tech/newsid_334000/334517.stm ], a new light must suddenly have appeared in the night sky and faded after a few weeks. Today we know this light was an exploding star [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/supernovae.html ] and record the colorful expanding cloud as the Veil Nebula [ http://nineplanets.org/twn/cygnusx.html ]. Pictured above [ http://robgendler.astrodigitals.com/Nebulas.html ] is the west end of the Veil Nebula [ http://www.astropix.com/HTML/E_SUM_N/VEIL.HTM ] known technically as NGC [ http://www.ngcic.com/dss/dss_images.htm ] 6960 but less formally as the Witch's Broom Nebula. The rampaging gas gains its colors by impacting and exciting existing [ http://antwrp.gsfc.nasa.gov/apod/ap960307.html ] nearby gas. The supernova remnant [ http://antwrp.gsfc.nasa.gov/apod/supernova_remnants.html ] lies about 1400 light-years away towards the constellation of Cygnus [ http://www.multimania.com/cdadfs/constellation/cygne/cygnus.htm ]. This Witch's Broom actually spans over three times the angular size of the full Moon [ http://antwrp.gsfc.nasa.gov/apod/moon.html ]. The bright blue star 52 Cygnus [ http://www.seds.org/Maps/Stars_en/Fig/cygnus.html ] is visible with the unaided eye from a dark location but unrelated to the ancient supernova [ http://www.chapman.edu/oca/benet/intro_sn.htm ]. |
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The Helix Nebula from CFHT
| Title |
The Helix Nebula from CFHT |
| Explanation |
One day our Sun may look like this. The Helix Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap960417.html ] is the closest example of a planetary nebula [ http://antwrp.gsfc.nasa.gov/apod/planetary_nebulae.html ] created at the end of the life of a Sun-like star. The outer gasses of the star expelled into space [ http://www.seds.org/messier/planetar.html ] appear from our vantage point as if we are looking down a helix [ http://mathworld.wolfram.com/Helix.html ]. The remnant central stellar core, destined to become a white dwarf star [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/dwarfs.html ], glows in light so energetic [ http://snoopy.gsfc.nasa.gov/~orfeus2/ultraviolet.html ] it causes the previously expelled gas to fluoresce [ http://www.exploratorium.edu/xref/exhibits/fluorescent_tube.html ]. The Helix Nebula [ http://www-personal.umich.edu/~jstys/nebulae/ngc7293.html ], given a technical designation of NGC 7293 [ http://www.seds.org/messier/xtra/ngc/n7293.html ], lies 450 light-years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] away towards the constellation [ http://www.emufarm.org/~cmbell/myth/myth.html ] of Aquarius [ http://www.astronomical.org/constellations/aqr.html ] and spans 1.5 light-years. The above image was taken with the Canada-France-Hawaii Telescope [ http://www.cfht.hawaii.edu/ ] (CFHT) located atop a dormant volcano in Hawaii [ http://www.state.hi.us/ ], USA. A close-up of the inner edge [ http://antwrp.gsfc.nasa.gov/apod/ap970720.html ] of the Helix Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap970901.html ] shows unusual gas knots of unknown origin [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998ApJ...503..792B ]. |
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SH2 136: A Spooky Nebula
| Title |
SH2 136: A Spooky Nebula |
| Explanation |
The dark nebula SH2-136 appears to be celebrating Halloween [ http://en.wikipedia.org/wiki/Halloween ] all of the time. The complex process of star formation [ http://antwrp.gsfc.nasa.gov/apod/ap050621.html ] create dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ] clouds of many shapes [ http://antwrp.gsfc.nasa.gov/apod/ap050425.html ] and sizes [ http://antwrp.gsfc.nasa.gov/apod/ap050424.html ] -- it is human perception [ http://www.johnsadowski.com/big_spanish_castle.php ] that might identify a ghoulish creature [ http://www.benjerry.com/fun_stuff/holidays/halloween/games/whack_a_ghoul/index.cfm ], on the right of the above image [ http://www.caelumobservatory.com/obs/sh2-136.html ], chasing humans. Halloween's modern celebration retains historic roots in dressing to scare away the spirits of the dead. Since the fifth century BC, Halloween [ http://teacherlink.ed.usu.edu/TLRESOURCES/units/Byrnes-celebrations/halloween.html ] has been celebrated as a cross-quarter day [ http://www.astronomy.ohio-state.edu/~pogge/Ast161/Unit2/time.html ], a day halfway between an equinox [ http://antwrp.gsfc.nasa.gov/apod/ap040320.html ] (equal day / equal night) and a solstice [ http://www.candlegrove.com/solstice.html ] (minimum day / maximum night in the northern hemisphere). With our modern calendar, however, the real cross-quarter day [ http://en.wikipedia.org/wiki/Cross-quarter_day ] will occur next week. Other cross-quarter markers include Groundhog Day [ http://www.groundhog.org/faq/history.shtml ] and Walpurgis Night [ http://en.wikipedia.org/wiki/Walpurgis_Night ]. |
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IC 4628: The Prawn Nebula
| Title |
IC 4628: The Prawn Nebula |
| Explanation |
South of Antares [ http://antwrp.gsfc.nasa.gov/apod/ap060714.html ], in the tail of the nebula-rich [ http://antwrp.gsfc.nasa.gov/apod/ap060628.html ] constellation Scorpius, lies emission nebula IC 4628 [ http://www.aao.gov.au/images/captions/aat105.html ]. Nearby hot, massive stars, millions of years young, radiate the nebula [ http://en.wikipedia.org/wiki/H_II_region ] with invisible ultraviolet light, stripping electrons from atoms. The electrons eventually recombine with the atoms to produce the visible nebular glow [ http://vis.sdsc.edu/research/hayden2.html ]. This narrow band [ http://antwrp.gsfc.nasa.gov/apod/ap060324.html ] image adopts a typical false-color mapping [ http://hubblesite.org/gallery/behind_the_pictures/ meaning_of_color/eagle.shtml ] of the atomic emission, showing hydrogen emission in green hues, sulfur as red and oxygen as blue. At an estimated distance of 6,000 light-years, the region shown is about 250 light-years across. The nebula is also cataloged as [ http://antwrp.gsfc.nasa.gov/apod/ap060519.html ] Gum 56 for Australian astronomer Colin Stanley Gum, but seafood-loving astronomers might know [ http://seds.lpl.arizona.edu/messier/xtra/supp/ d-names.html ] this cosmic cloud as The Prawn Nebula [ http://www.martinpughastrophotography.id.au/ Nebulae/IC4628.htm ]. |
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Orion's Horsehead Nebula
| Title |
Orion's Horsehead Nebula |
| Explanation |
The Horsehead Nebula is one of the most famous nebulae on the sky. It is visible as the black indentation to the red emission nebula [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ] seen just to the right of center of the above photograph. The bright star near the center is located in the belt of the familiar constellation of Orion. The horse-head [ http://antwrp.gsfc.nasa.gov/apod/ap990519.html ] feature is dark because it is really an opaque dust [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#dust ] cloud which lies in front of the bright red emission nebula. Like clouds in Earth's atmosphere, this cosmic cloud has assumed a recognizable shape by chance. After many thousands of years, the internal motions of the cloud will alter its appearance. The emission nebula [ http://www.seds.org/billa/twn/types.html ]'s red color is caused by electrons [ http://www.aip.org/history/electron/ ] recombining with protons [ http://www.neutron.anl.gov/proton.htm ] to form hydrogen [ http://pearl1.lanl.gov/periodic/elements/1.html ] atoms. Also visible in the picture are blue reflection nebulae [ http://antwrp.gsfc.nasa.gov/apod/reflection_nebulae.html ], which preferentially reflect the blue light [ http://antwrp.gsfc.nasa.gov/apod/ap000227.html ] from nearby stars. |
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M17: Omega Nebula Star Facto
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| Title |
M17: Omega Nebula Star Factory |
| Explanation |
In the depths of the dark clouds of dust and molecular gas known as M17, stars continue to form. Visible in the above recently released representative-color photograph [ http://www.eso.org/outreach/press-rel/pr-2000/phot-24-00.html ] of M17 [ http://www.seds.org/messier/m/m017.html ] by the New Technology Telescope [ http://www.ls.eso.org/lasilla/Telescopes/NEWNTT/telescope/esontt.html ] are clouds so dark that they appear almost empty of near infrared light [ http://www.ipac.caltech.edu/Outreach/Edu/discovery.html ]. The darkness of these molecular clouds [ http://antwrp.gsfc.nasa.gov/apod/ap990511.html ] results from background starlight being absorbed by thick carbon-based smoke-sized dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ]. As bright massive stars form, they produce intense and energetic light that slowly boils away [ http://antwrp.gsfc.nasa.gov/apod/ap990502.html ] the dark shroud. M17 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999AAS...195.7914K ]'s unusual appearance [ http://www.limber.org/m17fid.html ] has garnered it such nicknames as the Omega Nebula, the Horseshoe Nebula, and the Swan Nebula. M17 [ http://antwrp.gsfc.nasa.gov/apod/ap990126.html ], visible with binoculars towards the constellation of Sagittarius [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Sagittarius.html ], lies 5000 light-years [ http://www.howstuffworks.com/question94.htm ] away and spans 20 light-years across. |
|
The Cat's Eye Nebula
| Title |
The Cat's Eye Nebula |
| Explanation |
Three thousand light-years away, a dying star throws off shells of glowing gas. This image [ http://hubblesite.org/newscenter/archive/releases/1995/01/image/a/ ] from the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap010806.html ] reveals the Cat's Eye Nebula [ http://en.wikipedia.org/wiki/Cat%27s_Eye_Nebula ] to be one of the most complex [ http://www.astro.washington.edu/balick/WFPC2/ ] planetary nebulae [ http://en.wikipedia.org/wiki/Planetary_nebula ] known. In fact [ http://antwrp.gsfc.nasa.gov/apod/ap990916.html ], the features seen in the Cat's Eye [ http://antwrp.gsfc.nasa.gov/apod/ap010111.html ] are so complex that astronomers suspect the bright central object may actually be a binary star system [ http://antwrp.gsfc.nasa.gov/apod/ap970219.html ]. The term planetary nebula [ http://antwrp.gsfc.nasa.gov/apod/ap010805.html ], used to describe this general class of objects, is misleading. Although these objects may appear round and planet-like in small telescopes, high resolution images [ http://www.noao.edu/jacoby/pn_gallery.html ] reveal them to be stars surrounded by cocoons of gas blown off in the late stages of stellar evolution [ http://instruct1.cit.cornell.edu/courses/astro101/java/evolve/evolve.htm ]. |
|
M42: Wisps of the Orion Nebu
…
| Title |
M42: Wisps of the Orion Nebula |
| Explanation |
The Great Nebula in Orion [ http://www.seds.org/billa/twn/n1976x.html ], an immense, nearby starbirth region [ http://antwrp.gsfc.nasa.gov/apod/stellar_nurseries.html ], is probably the most famous of all astronomical nebulas [ http://www.seds.org/billa/twn/ ]. Here, glowing gas [ http://fusedweb.pppl.gov/CPEP/Chart_Pages/5.Plasmas/Nebula/Emission.html ] surrounds hot young stars at the edge of an immense [ http://antwrp.gsfc.nasa.gov/apod/ap971201.html ] interstellar molecular cloud [ http://antwrp.gsfc.nasa.gov/apod/ap030202.html ] only 1500 light-years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] away. In the above deep image [ http://christensenastroimages.com/nebula/m42_2005.htm ], faint wisps and sheets of dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ] and gas are particularly evident. The Great Nebula in Orion [ http://www.seds.org/messier/m/m042.html ] can be found with the unaided eye just below and to the left of the easily identifiable [ http://antwrp.gsfc.nasa.gov/apod/ap021225.html ] belt of three stars in the popular constellation [ http://www.astro.wisc.edu/~dolan/constellations/extra/constellations.html ] Orion [ http://www.astronomical.org/portal/modules/wfsection/article.php?articleid=60 ]. In addition to housing a bright open cluster [ http://antwrp.gsfc.nasa.gov/apod/open_clusters.html ] of stars known as the Trapezium [ http://antwrp.gsfc.nasa.gov/apod/ap971118.html ], the Orion Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap061120.html http://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search?Orion+Nebula ] contains many stellar nurseries [ http://archive.ncsa.uiuc.edu/Cyberia/Bima/StarForm.html ]. These nurseries contain hydrogen [ http://periodic.lanl.gov/elements/1.html ] gas, hot young stars, proplyds [ http://antwrp.gsfc.nasa.gov/apod/ap961017.html ], and stellar jets [ http://antwrp.gsfc.nasa.gov/apod/ap991129.html ] spewing material at high speeds. Also known as M42 [ http://antwrp.gsfc.nasa.gov/apod/ap020213.html ], the Orion Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap980421.html ] spans about 40 light years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] and is located in the same spiral arm [ http://www.anzwers.org/free/universe/5000lys.html ] of our Galaxy [ http://adc.gsfc.nasa.gov/mw/mmw_images.html ] as the Sun [ http://www.nineplanets.org/sol.html ]. |
|
IC 418: The Spirograph Nebul
…
| Title |
IC 418: The Spirograph Nebula |
| Explanation |
What is creating the strange texture of IC 418? Dubbed the Spirograph Nebula [ http://heritage.stsci.edu/public/2000sept7/ic418table.html ] for its resemblance to drawings from a cyclical drawing tool [ http://www.wordsmith.org/~anu/java/spirograph.html ], planetary nebula [ http://www.noao.edu/jacoby/pn_gallery.html ] IC 418 shows patterns [ http://mathworld.wolfram.com/Spirograph.html ] that are not well understood. Perhaps they are related to chaotic winds [ http://www-spof.gsfc.nasa.gov/Education/wsolwind.html ] from the variable central star, which changes brightness unpredictably [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997A%26A...320..125H ] in just a few hours. By contrast, evidence indicates that only a few million years ago, IC 418 [ http://www.skyhound.com/sh/archive/jan/IC_418.html ] was probably a well-understood star similar to our Sun [ http://www.seds.org/nineplanets/nineplanets/sol.html ]. Only a few thousand years ago, IC 418 was probably a common red giant [ http://www.historyoftheuniverse.com/starold.html ] star. Since running out of nuclear fuel [ http://csep10.phys.utk.edu/astr162/lect/energy/ppchain.html ], though, the outer envelope has begun expanding outward leaving a hot remnant core destined to become a white-dwarf star [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/dwarfs.html ], visible in the image [ http://heritage.stsci.edu/public/2000sept7/displayic418.html ] center. The light from the central core excites surrounding atoms [ http://www.pbs.org/wgbh/aso/tryit/atom/ ] in the nebula [ http://antwrp.gsfc.nasa.gov/apod/planetary_nebulae.html ] causing them to glow. IC 418 lies about 2000 light-years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] away and spans 0.3 light-years across. This recently released false-color image [ http://heritage.stsci.edu/public/2000sept7/ic418table.html ] taken from the Hubble Space Telescope [ http://www.stsci.edu/hst/ ] reveals the unusual details. |
|
The Nebula And The Neutron S
…
| Title |
The Nebula And The Neutron Star |
| Explanation |
The lonely RX J1856.5-3754 [ http://www.eso.org/outreach/press-rel/pr-2000/pr-19-00.html ] was formed from the collapsed core of an exploding star. At a distance of 180 light-years it is the closest known [ http://arXiv.org/abs/astro-ph/?0009031 ] neutron star. More massive than the Sun but only 20 kilometers across, this tiny stellar juggernaut plows through the hydrogen gas and dust clouds of interstellar space at about 200 kilometers per second. The surface of the neutron star [ http://www.astro.umd.edu/~miller/nstar.html ] is fantastically hot, around 700,000 degrees Celsius, making it detectable with orbiting x-ray telescopes. But optical astronomers were recently surprised to discover that RX J1856.5-3754 is also surrounded by a cone-shaped nebula. Indicated in this deep image from the European Southern Observatory's Kueyen telescope [ http://antwrp.gsfc.nasa.gov/apod/ap000707.html ], the nebula glows in the red light of ionized hydrogen atoms recombining with [ http://csep10.phys.utk.edu/astr162/lect/light/ absorption.html ] electrons. Its cone shape is analogous [ http://antwrp.gsfc.nasa.gov/apod/ap991127.html ] to the bow wave of a ship plowing through water. A faint blue dot near the tip of the cone is the neutron star itself. The nebula appears to have formed very near the surface [ http://antwrp.gsfc.nasa.gov/htmltest/rjn_bht.html ] of the neutron star and astronomers are trying to determine if the observed densities and temperatures can indeed explain the nebula's appearance. |
|
IC 2118: The Witch Head Nebu
…
| Title |
IC 2118: The Witch Head Nebula |
| Explanation |
Double, double toil and trouble, Fire burn, and cauldron bubble -- maybe Macbeth [ http://the-tech.mit.edu/Shakespeare/macbeth/ ] should have consulted the Witch Head Nebula. This suggestively shaped reflection nebula [ http://antwrp.gsfc.nasa.gov/apod/reflection_nebulae.html ] is associated with the bright star Rigel [ http://www.astro.uiuc.edu/~kaler/sow/rigel.html ] in the constellation Orion [ http://www.astro.uiuc.edu/~kaler/sow/orion-p.html ]. More formally known as IC 2118 [ http://www.astrocruise.com/ic2118.htm ], the Witch Head Nebula glows primarily by light reflected from bright star Rigel [ http://adsabs.harvard.edu/cgi-bin/ nph-bib_query?bibcode=1997MNRAS.290..521I ], located just off the upper right edge of the full image. Fine dust [ http://antwrp.gsfc.nasa.gov/apod/ap030706.html ] in the nebula reflects the light. The blue color is caused not only by Rigel [ http://en.wikipedia.org/wiki/Rigel ]'s blue color but because the dust grains reflect blue light [ http://leo.astronomy.cz/mix/mix.html ] more efficiently than red. The same physical process [ http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html ] causes Earth's daytime sky to appear blue [ http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html ], although the scatterers in Earth's atmosphere [ http://liftoff.msfc.nasa.gov/academy/space/atmosphere.html ] are molecules of nitrogen [ http://periodic.lanl.gov/elements/7.html ] and oxygen [ http://periodic.lanl.gov/elements/8.html ]. The nebula lies about 1000 light-years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] away. |
|
NGC 2174: Emission Nebula in
…
| Title |
NGC 2174: Emission Nebula in Orion |
| Explanation |
A lesser known sight in the nebula-rich [ http://antwrp.gsfc.nasa.gov/apod/ap061015.html ] constellation Orion, NGC 2174 [ http://www.astropix.com/HTML/B_WINTER/NGC2174.HTM ] can be found with binoculars near the head of the celestial hunter [ http://www.windows.ucar.edu/tour/link=/the_universe/ Constellations/orion.html&edu=high ]. About 6,400 light-years distant, the glowing cosmic cloud surrounds loose clusters of young stars. Covering an area larger than the full Moon on the sky, this stunning narrow band image [ http://www.photonhunter.com/nebulae/NGC2174.html ] adopts a typical color mapping of the atomic emission from NGC 2174. The false-color mapping [ http://hubblesite.org/gallery/behind_the_pictures/ meaning_of_color/eagle.shtml ] shows otherwise red hydrogen emission in green hues and emphasizes sulfur emission in red and oxygen in blue. Placing your cursor on the image will reveal an alternative image of the nebula made through broad band filters [ http://hubblesite.org/gallery/behind_the_pictures/ meaning_of_color/filters.shtml ]. The broad band image combines filters in a closer analogy [ http://hubblesite.org/gallery/behind_the_pictures/ meaning_of_color/rgb.shtml ] to human vision, dominated by the red glow [ http://antwrp.gsfc.nasa.gov/apod/ap060324.html ] of hydrogen. |
|
The Gum Nebula Supernova Rem
…
| Title |
The Gum Nebula Supernova Remnant |
| Explanation |
Because the Gum Nebula is the closest supernova remnant [ http://antwrp.gsfc.nasa.gov/apod/supernova_remnants.html ], it is actually hard to see. Spanning 40 degrees [ http://math.rice.edu/~pcmi/sphere/drg_txt.html ] across the sky, the nebula is so large and faint [ http://antwrp.gsfc.nasa.gov/apod/ap000412.html ] it is easily lost in the din of a bright and complex background. The Gum Nebula [ http://www.britannica.com/bcom/eb/article/idxref/3/0,5716,363760,00.html ], highlighted nicely in the above wide angle photograph [ http://www.celestialimage.com/page107.html ], is so close that we are much nearer the front edge than the back edge, each measuring 450 and 1500 light years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] respectively. The complex nebula [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1993A%26A...280..231S ] lies in the direction of the constellations [ http://aibn47.astro.uni-bonn.de/~gallery/constellations/const.html ] of Puppis [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Puppis.html ] and Vela [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Vela.html ]. Oddly, much remains unknown about the Gum Nebula [ http://www.edpsciences.org/articles/astro/abs/1997/07/ads1235/ads1235.html ], including the timing and even number of supernova explosions [ http://observe.ivv.nasa.gov/nasa/space/stellardeath/stellardeath_3.html ] that formed it. |
|
NGC 6960: The Witch's Broom
…
| Title |
NGC 6960: The Witch's Broom Nebula |
| Explanation |
Ten thousand years ago, before the dawn of recorded human history [ http://news.bbc.co.uk/hi/english/sci/tech/newsid_334000/334517.stm ], a new light must suddenly have appeared in the night sky and faded after a few weeks. Today we know this light was an exploding star [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/supernovae.html ] and record the colorful expanding cloud as the Veil Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap010928.html ]. Pictured above [ http://www.noao.edu/image_gallery/html/im0852.html ] is the west end of the Veil Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap030204.html ] known technically as NGC [ http://en.wikipedia.org/wiki/New_General_Catalog ] 6960 but less formally as the Witch [ http://antwrp.gsfc.nasa.gov/apod/ap061211.html ]'s Broom [ http://www.broomshop.com/history/ ] Nebula. The rampaging gas gains its colors by impacting and exciting existing [ http://www.seds.org/billa/twn/cygnusx.html ] nearby gas. The supernova remnant [ http://antwrp.gsfc.nasa.gov/apod/supernova_remnants.html ] lies about 1400 light-years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] away towards the constellation of Cygnus [ http://www.multimania.com/cdadfs/constellation/cygne/cygnus.htm ]. This Witch's Broom actually spans over three times the angular size [ http://imagine.gsfc.nasa.gov/YBA/HTCas-size/more-ang_size.html ] of the full Moon [ http://antwrp.gsfc.nasa.gov/apod/ap030810.html ]. The bright star 52 Cygnus [ http://www.seds.org/Maps/Stars_en/Fig/cygnus.html ] is visible with the unaided eye from a dark location but unrelated to the ancient supernova [ http://en.wikipedia.org/wiki/Supernova ]. |
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The Eagle Nebula in Infrared
| Title |
The Eagle Nebula in Infrared |
| Explanation |
In visible light, the whole thing looks like an eagle [ http://video.google.com/videoplay?docid=-4639730101975502715&q=eagle&hl=en ]. The region was captured recently in unprecedented detail in infrared light [ http://imagers.gsfc.nasa.gov/ems/infrared.html ] by the robotic orbiting Spitzer Space Telescope [ http://en.wikipedia.org/wiki/Spitzer_space_telescope ] (SSC). Shown above [ http://www.spitzer.caltech.edu/Media/releases/ssc2007-01/ssc2007-01a.shtml ], the infrared image allows observers to peer through normally opaque dust [ http://antwrp.gsfc.nasa.gov/apod/ap060409.html ] and so better capture the full complexity of the Eagle Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap060226.html ] star forming region. In particular, the three famous pillars [ http://antwrp.gsfc.nasa.gov/apod/ap050424.html ] near the image center are seen bathed in dust likely warmed by a supernova [ http://en.wikipedia.org/wiki/Supernova ] explosion. The warm dust is digitally assigned the false color of red. Also visible, near the bottom of the image, is ten light-year long pillar sometimes dubbed the Fairy [ http://antwrp.gsfc.nasa.gov/apod/ap050425.html ] of Eagle Nebula. The greater Eagle emission nebula [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ], tagged M16, lies about 6500 light years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] away, spans about 20 light-years, and is visible with binoculars [ http://www.birdwatching.com/optics/binoculars1.html#How Binoculars Work ] toward the constellation [ http://www.astro.wisc.edu/~dolan/constellations/extra/constellations.html ] of Serpens [ http://www.astronomical.org/portal/modules/wfsection/article.php?articleid=76 ]. |
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IC 5067: Emission Nebula Clo
…
| Title |
IC 5067: Emission Nebula Close-up |
| Explanation |
This amazing skyscape [ http://www.rc-astro.com/php/displayImage.htm?id=1013 ] lies along a bright ridge of emission in IC 5067, also known as The Pelican Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap061130.html ]. Appropriately, the Pelican Nebula itself is part of a much larger, complex star-forming region about 2,000 light-years away in the high flying constellation Cygnus, the Swan [ http://www.windows.ucar.edu/tour/link=/the_universe/ Constellations/summer/cygnus.html&edu=high ]. Cosmic dust clouds that span light-years seem to rise like mountains in the mist in this natural color view, recorded through broadband filters to produce [ http://hubblesite.org/gallery/behind_the_pictures/ meaning_of_color/rgb.shtml ] an analogy to human color vision [ http://en.wikipedia.org/wiki/Color_vision ]. The fantastic shapes are sculpted by winds and radiation from a hot, massive stars and the dominant red emission is due to atomic hydrogen [ http://antwrp.gsfc.nasa.gov/apod/ap051223.html ] gas. Placing your cursor on the image will bring up a false color image of the nebula made through narrowband filters that also map specific emission from sulfur and oxygen atoms. The mapped color [ http://antwrp.gsfc.nasa.gov/apod/ap060324.html ] image reveals even more details of the cosmic clouds and their composition. |
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The Orion Nebula in Hydrogen
| Title |
The Orion Nebula in Hydrogen |
| Explanation |
The Great Nebula in Orion [ http://nineplanets.org/twn/n1976x.html ] can be found just below and to the left of the easily identifiable belt of three stars in the popular constellation Orion [ http://www.seds.org/Maps/Stars_en/Fig/orion.html ]. This fuzzy patch, visible to the unaided eye [ http://antwrp.gsfc.nasa.gov/apod/ap970825.html ], contains one of the closest stellar nurseries [ http://antwrp.gsfc.nasa.gov/apod/stellar_nurseries.html ], lying at a distance of about 1500 light years [ http://www.howstuffworks.com/question94.htm ]. The above picture [ http://robgendler.astrodigitals.com/Nebulas.html ] highlights red light emitted by the nebula's hydrogen [ http://school.discovery.com/homeworkhelp/worldbook/atozscience/h/268980.html ] gas. Dark dust [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#dust ] filaments punctuate regions of this glowing hydrogen gas and reflect light from the nebula's brightest stars [ http://antwrp.gsfc.nasa.gov/apod/ap971118.html ]. Recent observations of the Orion Nebula [ http://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search?m42 ] by the Hubble Space Telescope [ http://www.stsci.edu/hst/ ] have located solar-system sized regions [ http://antwrp.gsfc.nasa.gov/apod/ap990228.html ] that are thought to be planet-forming circumstellar disks. |
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Composing the Omega Nebula
| Title |
Composing the Omega Nebula |
| Explanation |
The Omega Nebula is a massive, complex cloud of dust [ http://eta.pha.jhu.edu/~danforth/superfit/superfit.html ] and gas from which new stars are continually forming. The similarity to the Greek letter [ http://www.nadin00.freeserve.co.uk/maths/greek.htm ] capital Omega gives the molecular cloud [ http://antwrp.gsfc.nasa.gov/apod/ap990511.html ] its popular name, but the nebula is also known as the Swan [ http://www.encarta.msn.com/index/conciseindex/58/0589E000.htm ] Nebula, the Horseshoe Nebula, and M17 [ http://antwrp.gsfc.nasa.gov/apod/ap000919.html ]. Detailed features such as thin filaments [ http://antwrp.gsfc.nasa.gov/apod/ap980208.html ] of emission by diffuse dust and dark clouds [ http://antwrp.gsfc.nasa.gov/apod/ap960925.html ] of absorption by dense dust are visible in this recently released picture [ http://www.noao.edu/image_gallery/html/im0627.html ]. The image highlights infrared light [ http://www.ktca.org/newtons/11/infrared.html ] emitted by large molecules [ http://www.exploratorium.edu/xref/phenomena/atoms_and_molecules.html ] known as polycyclic aromatic hydrocarbons [ http://www-space.arc.nasa.gov/~sloan/research/pah_info.html ] (PAHs), a gas similar to car exhaust [ http://www.ns.ec.gc.ca/epb/envfacts/pah.html ] that traces carbon [ http://pearl1.lanl.gov/periodic/elements/6.html ] and interstellar dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ]. PAHs [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996A%26A...315..194H ] may be an intermediate step between smaller molecules and large interstellar dust [ http://antwrp.gsfc.nasa.gov/apod/ap990919.html ] grains. The origin of PAHs [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999AAS...194.4106S ] is currently unknown but thought by some astronomers to form in the cool atmospheres of young carbon stars [ http://www.itss.raytheon.com/cafe/qadir/q995.html ] and to be dispersed by their stellar winds [ http://antwrp.gsfc.nasa.gov/apod/ap000318.html ]. |
|
Flame Nebula Close-Up
| Title |
Flame Nebula Close-Up |
| Explanation |
Of course, the Flame Nebula is not on fire. Also known as NGC 2024 [ http://www.astropix.com/HTML/B_WINTER/NGC2024.HTM ], the nebula's suggestive reddish color is due to the glow of hydrogen [ http://antwrp.gsfc.nasa.gov/apod/lib/lament.html ] atoms at the edge of the giant Orion [ http://antwrp.gsfc.nasa.gov/apod/ap070125.html ] molecular cloud complex some 1,500 light-years away. The hydrogen atoms have been ionized [ http://csep10.phys.utk.edu/astr162/lect/light/ ionization.html ], or stripped of their electrons, and glow as the atoms and electrons recombine. But what ionizes the hydrogen [ http://casswww.ucsd.edu/public/tutorial/ISM.html ] atoms? In this close-up view [ http://www.robgendlerastropics.com/FlameNM.html ], a dark lane of absorbing interstellar dust stands out in silhouette against the hydrogen glow [ http://vis.sdsc.edu/research/hayden2.html ] and actually hides the true source of the Flame Nebula's energy from optical telescopes. Behind the dark lane lies a cluster of hot, young stars, seen at infrared wavelengths [ http://www.astro.caltech.edu/palomar/flame.html ] through the obscuring dust. A young, massive star in that cluster is the likely source [ http://arxiv.org/abs/astro-ph/0303029 ] of energetic ultraviolet radiation that ionizes the hydrogen gas in the Flame Nebula. |
|
The Dark Horsehead Nebula
| Title |
The Dark Horsehead Nebula |
| Explanation |
While drifting through the cosmos this magnificent interstellar dust cloud, sculpted by stellar winds and radiation, has chanced to assume a recognizable shape. Fittingly named The Horsehead Nebula [ http://www.seds.org/billa/twn/b33x.html ] it is embedded in the immense complex of star forming gas and dust [ http://antwrp.gsfc.nasa.gov/apod/ap000924.html ] surrounding the Orion Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap990522.html ] some 1,500 light-years distant. The dark nebula [ http://antwrp.gsfc.nasa.gov/apod/dark_nebulae.html ] is cataloged as Barnard [ http://astro.uchicago.edu/yerkes/ virtualmuseum/Barnard.html ] 33 and is visible only because its obscuring dust is silhouetted against the bright emission nebulae [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ] which lie behind it. In fact, the prominent horse head portion [ http://antwrp.gsfc.nasa.gov/apod/ap980806.html ] of the nebula is really just part of a larger cloud of dust which can be seen extending off the bottom of the picture. A potentially rewarding but difficult object to view with a small instrument, this gorgeous color image [ http://www.ghg.net/akelly/ ] is a composite of exposures made with a digital camera and astronomical BVR filters [ http://herbie.ucolick.org/techdocs/ filters/phot_filt_curves.html ] using a 1-meter diameter telescope. |
|
M8: In the Center of the Lag
…
| Title |
M8: In the Center of the Lagoon Nebula |
| Explanation |
In the center of the Lagoon Nebula [ http://www.seds.org/messier/m/m008.html ] one finds glowing gas [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ], star clusters, and dense knots of gas and dust [ http://antwrp.gsfc.nasa.gov/apod/ap961229.html ] just now forming stars. The young open cluster [ http://antwrp.gsfc.nasa.gov/apod/open_clusters.html ] of stars, designated NGC 6523, can be seen in the center of the above image [ http://www.janis.or.jp/users/kitahara/e-m8-95.jpg.html ]. These stars emit energetic light [ http://snoopy.gsfc.nasa.gov/~orfeus2/ultraviolet.html ] that ionizes [ http://csep10.phys.utk.edu/astr162/lect/light/ionization.html ] the surrounding hydrogen [ http://pearl1.lanl.gov/periodic/elements/1.html ] gas. As this gas reacquires electrons [ http://www.aip.org/history/electron/ ], it emits red light [ http://csep10.phys.utk.edu/astr162/lect/light/absorption.html ]. The Lagoon Nebula [ http://www.seds.org/billa/twn/n6523x.html ] lies about 5000 light-years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] away and spans about 100 light-years across. The nebula [ http://antwrp.gsfc.nasa.gov/apod/ap980707.html ] occupies an area on the sky larger than a full moon [ http://antwrp.gsfc.nasa.gov/apod/ap991108.html ], and can be seen even without binoculars from a dark location towards the constellation [ http://www.allthesky.com/constellations/const.html ] of Sagittarius [ http://www.astronomical.org/constellations/sgr.html ]. |
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Planetary Nebula NGC 2440
| Title |
Planetary Nebula NGC 2440 |
| Explanation |
Planetary nebula [ http://en.wikipedia.org/wiki/Planetary_nebula ] NGC 2440 has an intriguing bow-tie [ http://www.folds.net/bowtie/ ] shape in this stunning view [ http://hubblesite.org/newscenter/archive/releases/2007/09/ ] from space. The nebula is composed of material cast off by a dying sun-like star as it enters its white dwarf phase [ http://antwrp.gsfc.nasa.gov/apod/ap060507.html ] of evolution. Details of remarkably complex structures are revealed within [ http://adsabs.harvard.edu/abs/1998ApJ...493..803L ] NGC 2440, including dense ridges of material swept back from the nebula's central star. Near the center of the view, the star itself is one of the hottest known [ http://antwrp.gsfc.nasa.gov/apod/ap951130.html ], with a surface temperature of about 200,000 kelvins [ http://lamar.colostate.edu/~hillger/temps.htm ]. About 4,000 light-years from planet Earth toward the nautical constellation Puppis [ http://hawastsoc.org/deepsky/pup/index.html ], the nebula spans over a light-year and is energized by ultraviolet light from the central star. The false-color image [ http://archive.stsci.edu/prepds/heritage/ngc2440/index.html ] was recorded earlier this month using the Hubble's Wide-Field Planetary Camera 2(WFPC2), demonstrating still impressive imaging capabilities following the failure of the Advanced Camera for Surveys. |
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X-rays and the Eagle Nebula
| Title |
X-rays and the Eagle Nebula |
| Explanation |
The premier Chandra X-ray Observatory images of M16 [ http://chandra.harvard.edu/photo/2007/m16/ ], the Eagle Nebula, show many bright x-ray sources in the region. Most of the x-ray sources [ http://chandra.harvard.edu/xray_astro/medxray.html ] are energetic young stars. They are seen here as colored spots superimposed on the Hubble's well-known optical view of M16's light-year long Pillars of Creation [ http://antwrp.gsfc.nasa.gov/apod/ap070218.html ]. For example, a blue source near [ http://chandra.harvard.edu/photo/2007/m16/zoom.html ] the tip of the large pillar at the upper left is estimated to be an embedded young star 4 or 5 times as massive as the Sun [ http://www.sunblock99.org.uk/sb99/fact/ heavy.html ]. Still, most of the x-ray sources are not coincident with the pillars themselves, indicating that embedded stars are not common in the dusty structures. The mostly empty pillars are thought to be an indication [ http://arxiv.org/abs/astro-ph/0610279 ] that star formation actually peaked millions of years ago within [ http://arxiv.org/abs/astro-ph/0201292 ] the Eagle Nebula [ http://seds.lpl.arizona.edu/messier/m/m016.html ]. |
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