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Spiral Galaxy NGC 2403 from …
Title Spiral Galaxy NGC 2403 from Subaru
Explanation Sprawling spiral arms dotted with bright red emission nebulas [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ] highlight this new and detailed image of nearby spiral galaxy [ http://antwrp.gsfc.nasa.gov/apod/spiral_galaxies.html ] NGC 2403. Also visible in the photogenic spiral galaxy [ http://en.wikipedia.org/wiki/Spiral_galaxy ] are blue open clusters [ http://antwrp.gsfc.nasa.gov/apod/open_clusters.html ], dark dust [ http://antwrp.gsfc.nasa.gov/apod/ap030706.html ] lanes [ http://antwrp.gsfc.nasa.gov/apod/ap020620.html ], and a bright but relatively small central nucleus [ http://antwrp.gsfc.nasa.gov/apod/ap001220.html ]. NGC 2403 is located just beyond the Local Group of Galaxies [ http://en.wikipedia.org/wiki/Local_group ], at a relatively close 10 million light years away toward the constellation [ http://www.astro.wisc.edu/~dolan/constellations/extra/constellations.html ] of the Giraffe [ http://www.kidsplanet.org/factsheets/giraffe.html ] (Camelopardalis [ http://www.astronomical.org/portal/modules/wfsection/article.php?articleid=11 ]). NGC 2403 has a designated Hubble type [ http://en.wikipedia.org/wiki/Hubble_sequence ] of Sc. In 2004, NGC 2403 was home to one of the brightest supernovas [ http://antwrp.gsfc.nasa.gov/apod/ap040907.html ] of modern times. The above image [ http://subarutelescope.org/Pressrelease/2005/10/13/index.html ], the highest resolution complete image of NGC 2403 ever completed, was taken by the Japan [ http://www.cia.gov/cia/publications/factbook/geos/ja.html ]'s 8.3-meter Subaru telescope [ http://www.schoolsobservatory.org.uk/astro/textb/tele/world/subaru.htm ] located on Mauna Kea [ http://antwrp.gsfc.nasa.gov/apod/ap051220.html ], Hawaii [ http://en.wikipedia.org/wiki/Hawaii ], USA [ http://www.cdc.noaa.gov/USclimate/states.fast.html ].
Unusual Starburst Galaxy NGC …
Title Unusual Starburst Galaxy NGC 1313
Explanation Why is this galaxy so discombobulated? Usually, galaxies this topsy-turvy [ http://video.google.com/videoplay?docid=5403974888855118935 ] result from a recent collision with a neighboring galaxy. Spiral galaxy [ http://antwrp.gsfc.nasa.gov/apod/spiral_galaxies.html ] NGC 1313, however, appears to be alone. Brightly lit with new and blue massive stars, star formation appears so rampant in NGC 1313 [ http://www.eso.org/outreach/press-rel/pr-2006/phot-43-06.html ] that it has been labeled a starburst galaxy [ http://en.wikipedia.org/wiki/Starburst_galaxy ]. Strange features of NGC 1313 [ http://www.aao.gov.au/images/deep_html/n1313_d.html ] include that its spiral arms are lopsided and its rotational axis is not at the center of the nuclear bar. Pictured above [ http://www.eso.org/outreach/press-rel/pr-2006/pr-43-06.html ], NGC 1313 spans about 50,000 light years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] and lies only about 15 million light years away toward the constellation [ http://en.wikipedia.org/wiki/Constellation ] of Reticulum [ http://en.wikipedia.org/wiki/Reticulum_constellation ]. Continued numerical modeling [ http://ifa.hawaii.edu/~barnes/transform.html ] of galaxies like NGC 1313 might shed some light on its unusual nature.
Dwarf Elliptical Galaxy NGC …
Title Dwarf Elliptical Galaxy NGC 205 in the Local Group
Explanation Our Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/milky_way.html ] is not alone. It is part of a gathering of about 25 galaxies known as the Local Group [ http://www.seds.org/messier/more/local.html ]. Members include the Great Andromeda Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap991114.html ] (M31), M32 [ http://antwrp.gsfc.nasa.gov/apod/ap991103.html ], M33 [ http://antwrp.gsfc.nasa.gov/apod/ap980721.html ], the Large Magellanic Cloud [ http://antwrp.gsfc.nasa.gov/apod/ap000222.html ], the Small Magellanic Cloud [ http://antwrp.gsfc.nasa.gov/apod/ap000430.html ], Dwingeloo 1 [ http://antwrp.gsfc.nasa.gov/apod/ap000109.html ], several small irregular galaxies [ http://www.seds.org/messier/irre.html ], and many dwarf elliptical [ http://nedwww.ipac.caltech.edu/level5/Ferguson/frames.html ] and dwarf spheroidal galaxies [ http://www.astro.uu.se/~ns/review.html ]. Pictured [ http://www.cfht.hawaii.edu/Science/Astros/Imageofweek/ciw061299.html ] on the lower left is one of the many dwarf ellipticals [ http://www.astro.psu.edu/users/pdurrell/dE.html ]: NGC 205 [ http://www.seds.org/messier/m/m110.html ]. Like M32 [ http://www.seds.org/messier/m/m032.html ], NGC 205 [ http://nedwww.ipac.caltech.edu/level5/Hodge/Hodge5_5.html ] is a companion to the large M31, and can sometimes be seen to the south of M31 [ http://www.seds.org/messier/m/m031.html ]'s center in photographs. The above image [ http://www.cfht.hawaii.edu/Science/Astros/Imageofweek/ciw061299.html ] shows NGC 205 to be unusual [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998ApJ...499..209W ] for an elliptical galaxy [ http://antwrp.gsfc.nasa.gov/apod/elliptical_galaxies.html ] in that it contains at least two dust clouds [ http://antwrp.gsfc.nasa.gov/apod/ap990919.html ] (at 1 and 4 o'clock - they are visible but hard to spot) and signs of recent star formation [ http://antwrp.gsfc.nasa.gov/apod/stellar_nurseries.html ]. This galaxy is sometimes known as M110, although it was actually not part of Messier [ http://antwrp.gsfc.nasa.gov/apod/ap960626.html ]'s original catalog [ http://antwrp.gsfc.nasa.gov/apod/messier.html ].
NGC 2244: A Star Cluster in …
Title NGC 2244: A Star Cluster in the Rosette Nebula
Explanation In the heart of the Rosette Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap000111.html ] lies a bright open cluster [ http://antwrp.gsfc.nasa.gov/apod/open_clusters.html ] of stars that lights up the nebula. The stars of NGC 2244 [ http://www.seds.org/messier/xtra/ngc/n2244.html ] formed from the surrounding gas only four million years ago [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1993ApJ...414..664K ] and emit light and wind that define the nebula's appearance [ http://www.cfht.hawaii.edu/Science/Astros/Imageofweek/ciw310100.html ] today. High energy light from the bright young stars [ http://antwrp.gsfc.nasa.gov/apod/ap010506.html ] of NGC 2244 ionizes the surrounding hydrogen gas [ http://pearl1.lanl.gov/periodic/elements/1.html ] clouds to create the red emission nebula [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ] appearance. The hot wind [ http://science.msfc.nasa.gov/ssl/pad/solar/sun_wind.htm ] of particles that streams away from the cluster stars contributes to an already complex menagerie of gas and dust [ http://antwrp.gsfc.nasa.gov/apod/ap010813.html ] filaments while slowly evacuating the cluster center. NGC 2244 [ http://antwrp.gsfc.nasa.gov/apod/ap980214.html ] measures about 50 light-years [ http://einstein.stcloudstate.edu/Dome/constellns/lightyear.html ] across, lies about 4500 light-years away [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26A...358..553H ], and is visible with binoculars towards the constellation [ http://www.physics.csbsju.edu/astro/asp/constellation.faq.html ] of Monoceros [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Monoceros.html ].
NGC 3621: Far Beyond the Loc …
Title NGC 3621: Far Beyond the Local Group
Explanation Far beyond [ http://arxiv.org/abs/astro-ph/0012372 ] the local group [ http://www.anzwers.org/free/universe/localgr.html ] of galaxies lies NGC 3621 [ http://www.seds.org/~spider/ngc/ngc.cgi?3621 ], some 22 million light-years away. Found in the serpentine southern constellation Hydra [ http://www.astronomical.org/constellations/hya.html ], the loose spiral arms of this gorgeous island universe [ http://www.astr.ua.edu/goodies/data_resources/ galaxies.text ] are loaded with luminous young star clusters and dark dust lanes. Still, for earthbound astronomers NGC 3621 is not just another [ http://antwrp.gsfc.nasa.gov/apod/ap011004.html ] pretty face-on spiral galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap010427.html ]. Some of its brighter stars [ http://www.ipac.caltech.edu/H0kp/n3621/n3621.html ] have been used as standard candles [ http://www.powersof10.com/powers/tools/station_232.html ] to establish [ http://oposite.stsci.edu/pubinfo/PR/1999/19/ background.html ] important estimates of extragalactic distances [ http://casswww.ucsd.edu/public/tutorial/ Distances.html ] and the scale of the Universe [ http://antwrp.gsfc.nasa.gov/debate/debate96.html ]. This color picture was constructed from astronomical image data recorded with the Very Large Telescope Antu [ http://antwrp.gsfc.nasa.gov/apod/ap000707.html ], at Paranal Observatory in Chile. At the original resolution, individual, hot supergiant stars [ http://www.usm.uni-muenchen.de/people/kud/ windsfromhotstars/winds.html ] can be identified and studied across NGC 3621.
Interstellar Dust Bunnies of …
Title Interstellar Dust Bunnies of NGC 891
Explanation What is going on in NGC 891 [ http://antwrp.gsfc.nasa.gov/apod/ap970228.html ]? This galaxy appeared previously to be very similar to our own Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap000130.html ]: a spiral galaxy [ http://www.astr.ua.edu/goodies/data_resources/galaxies.text ] seen nearly edge-on. However, recent [ http://www.cfht.hawaii.edu/HawaiianStarlight/English/Poster-NGC891.html ] high-resolution images [ http://antwrp.gsfc.nasa.gov/apod/ap990919.html ] of NGC 891 [ http://www.seds.org/messier/xtra/ngc/n0891.html ]'s dust show unusual filamentary patterns extending well away from its Galactic disk. This interstellar dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ] was probably thrown out of the galactic disk toward the halo [ http://www.eso.org/outreach/press-rel/pr-1999/pr-04-99.html ] by stellar supernovae explosions [ http://heasarc.gsfc.nasa.gov/docs/snr.html ]. Because dust is so fragile, its appearance after surviving disk expulsion can be very telling [ http://antwrp.gsfc.nasa.gov/apod/ap020703.html http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26A...362..138P ]. Newly discovered phenomena, however, sometimes appear so complex [ http://antwrp.gsfc.nasa.gov/apod/ap980310.html ] that more questions are raised than are answered.
Open Cluster NGC 6520 from C …
Title Open Cluster NGC 6520 from CFHT
Explanation Did you ever have a day when it felt like a dark cloud [ http://antwrp.gsfc.nasa.gov/apod/ap010923.html ] was following you around? For the open cluster [ http://www.seds.org/messier/open.html ] of stars NGC 6520, every day is like this. On the left of the above picture [ http://www.cfht.hawaii.edu/HawaiianStarlight/AIOM/English/CFHT-Coelum-AIOM.html ] are many of NGC 6520's bright blue stars. They formed only millions of years ago - much more recently than our ancient Sun which formed billions of years ago. On the right is an absorption nebula [ http://antwrp.gsfc.nasa.gov/apod/dark_nebulae.html ], molecular cloud [ http://origins.jpl.nasa.gov/poster/bigbang3.html ] Barnard 86 [ http://astro.uchicago.edu/yerkes/virtualmuseum/Barnard.html ], from which the stars of NGC 6520 surely formed. This nebula contains much opaque dust [ http://antwrp.gsfc.nasa.gov/apod/ap010813.html ] that blocks light from the many stars that would have been visible in the background. Surrounding NGC 6520 [ http://www.ast.cam.ac.uk/AAO/images/captions/aat092.html ] is part of the tremendously dense starscape in the bulge of our Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap970315.html ], the extended halo of stars that surrounds the center [ http://antwrp.gsfc.nasa.gov/apod/ap010708.html ] of our Galaxy. NGC 6520 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1982S%26T....63..254M ] spans about 10 light years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] and lies about 5500 light years away toward the direction of Sagittarius [ http://www.astronomical.org/constellations/sgr.html ].
The Supermassive Black Holes …
Title The Supermassive Black Holes of NGC 6240
Explanation The Hubble [ http://www.ifa.hawaii.edu/~barnes/hon6240.html ] optical image on the left shows NGC 6240 [ http://crux.astr.ua.edu/gifimages/ngc6240.html ] in the throes [ http://antwrp.gsfc.nasa.gov/apod/ap020411.html ] of a titanic galaxy - galaxy collision 400 million light-years away. As the cosmic catastrophe plays out, the merging galaxies spew forth distorted tidal tails [ http://antwrp.gsfc.nasa.gov/apod/ap020502.html ] of stars, gas, and dust and undergo frantic bursts [ http://antwrp.gsfc.nasa.gov/apod/ap020711.html ] of star formation. Using the orbiting Chandra [ http://chandra.harvard.edu/chronicle/ ] Observatory's x-ray vision to peer within the bright central regions of NGC 6240 astronomers believe they have uncovered, for the first time [ http://chandra.harvard.edu/photo/2002/0192/index.html ], not one but two enormous orbiting black holes [ http://antwrp.gsfc.nasa.gov/apod/ap000914.html ], by detecting the characteristic x-ray radiation from the interstellar debris swirling [ http://antwrp.gsfc.nasa.gov/apod/ap020927.html ] toward them. In the false-color close-up view at right, the x-ray data clearly show the black hole sources (shaded blue) separated by about 3,000 light-years. Einstein's theory of gravity predicts that such a pair of black holes must spiral closer together, and ultimately coalesce [ http://chandra.harvard.edu/photo/2002/0192/ animations.html ] into a single, even more massive black hole after [ http://chandra.harvard.edu/photo/cosmic_lookback.html ] several hundred million years [ http://chandra.harvard.edu/photo/cosmic_lookback.html ]. In the final moments the merging supermassive black holes will produce an extremely powerful burst of gravitational radiation [ http://archive.ncsa.uiuc.edu/Cyberia/NumRel/ GravWaves.html ].
NGC 281: Cluster, Clouds, an …
Title NGC 281: Cluster, Clouds, and Globules
Explanation NGC 281 [ http://www.seds.org/~spider/ngc/ngc.cgi?ngc281 ] is a busy workshop of star formation. Prominent features include a small open cluster [ http://antwrp.gsfc.nasa.gov/apod/ap010909.html ] of stars, a diffuse red-glowing emission nebula [ http://www.seds.org/messier/nebula.html ], large lanes of obscuring gas [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#hydrogen ] and dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ], and dense knots of dust and gas in which stars may still be forming. The open cluster [ http://antwrp.gsfc.nasa.gov/apod/open_clusters.html ] of stars IC 1590 visible around the center has formed only in the last few million years. The brightest member of this cluster is actually a multiple-star system [ http://antwrp.gsfc.nasa.gov/apod/ap970219.html ] shining light that helps ionize the nebula's gas, causing the red glow visible throughout. The lanes of dust [ http://antwrp.gsfc.nasa.gov/apod/ap980121.html ] visible below the center are likely homes of future star formation [ http://antwrp.gsfc.nasa.gov/apod/ap011125.html ]. Particularly striking in the above photograph [ http://www.cfht.hawaii.edu/HawaiianStarlight/AIOM/English/CFHT-Coelum- AIOM-Apr2003.html ] are the dark Bok globules [ http://antwrp.gsfc.nasa.gov/apod/ap030127.html ] visible against the bright nebula. Stars are surely forming there right now. The entire NGC 281 [ http://adsabs.harvard.edu/cgi-bin/nph- bib_query?bibcode=1996AAS...188.4206G ] system lies about 10 thousand light years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] distant.
Spiral Galaxy NGC 253 Almost …
Title Spiral Galaxy NGC 253 Almost Sideways
Explanation NGC 253 is a normal spiral galaxy [ http://www.seds.org/messier/spir.html ] seen here almost sideways. It is the largest member of the Sculptor Group of Galaxies [ http://www.seds.org/messier/xtra/ngc/sclgr.html ], the nearest group [ http://csep10.phys.utk.edu/astr162/lect/gclusters/groups.html ] to our own Local Group [ http://csep10.phys.utk.edu/astr162/lect/gclusters/localg.html ] of Galaxies. NGC 253 [ http://antwrp.gsfc.nasa.gov/apod/ap030316.html ], pictured above [ http://www.cfht.hawaii.edu/HawaiianStarlight/AIOM/English/CFHT-Coelum-AIOM-May2003.html ], appears visually as one of the brightest spirals [ http://antwrp.gsfc.nasa.gov/apod/spiral_galaxies.html ] on the sky, and is easily visible in southern hemisphere [ http://antwrp.gsfc.nasa.gov/apod/ap021222.html ] with a good pair of binoculars [ http://www.birdwatching.com/optics/binoculars1.html#How%20Binoculars%20Work ]. The type Sc galaxy [ http://zebu.uoregon.edu/~js/ast123/lectures/lec13.html ] is about 10 million light years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] distant. NGC 253 [ http://antwrp.gsfc.nasa.gov/apod/ap010607.html ] is considered a starburst galaxy [ http://chandra.harvard.edu/xray_sources/starburst.html ] because of high star formation rates and dense dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ] clouds in its nucleus. The energetic nuclear region is seen to glow in X-ray [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#X-ray ] and gamma-ray [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html ] light.
NGC 3621: Far Beyond the Loc …
Title NGC 3621: Far Beyond the Local Group
Explanation Far beyond [ http://arxiv.org/abs/astro-ph/0012372 ] the local group [ http://www.anzwers.org/free/universe/localgr.html ] of galaxies lies NGC 3621 [ http://www.seds.org/~spider/ngc/ngc.cgi?3621 ], some 22 million light-years away. Found in the serpentine southern constellation Hydra [ http://www.astronomical.org/constellations/hya.html ], the loose spiral arms of this gorgeous island universe [ http://www.astr.ua.edu/goodies/data_resources/ galaxies.text ] are loaded with luminous young star clusters and dark dust lanes. Still, for earthbound astronomers NGC 3621 is not just another [ http://antwrp.gsfc.nasa.gov/apod/ap011004.html ] pretty face-on spiral galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap010427.html ]. Some of its brighter stars [ http://www.ipac.caltech.edu/H0kp/n3621/n3621.html ] have been used as standard candles [ http://www.powersof10.com/powers/tools/station_232.html ] to establish [ http://oposite.stsci.edu/pubinfo/PR/1999/19/ background.html ] important estimates of extragalactic distances [ http://casswww.ucsd.edu/public/tutorial/ Distances.html ] and the scale of the Universe [ http://antwrp.gsfc.nasa.gov/debate/debate96.html ]. This color picture was constructed from astronomical image data recorded with the Very Large Telescope Antu [ http://antwrp.gsfc.nasa.gov/apod/ap000707.html ], at Paranal Observatory in Chile. At the original resolution, individual, hot supergiant stars [ http://www.usm.uni-muenchen.de/people/kud/ windsfromhotstars/winds.html ] can be identified and studied across NGC 3621.
Copyright: AURA [ http://www …
Title Copyright: AURA [ http://www.aura-astronomy.org/ ] Explanation: This galaxy is having a bad millennium. In fact, the past 100 million years haven't been so good, and probably the next billion or so should be quite tumultuous. NGC 4039 [ http://adsbit.harvard.edu/cgi-bin/nph-article_query?bibcode=1995AJ%2E%2E%2E%2E109%2E%2E960W&page=1&plate_select=NO&type=GIF&nosetcookie=1 ] was a normal spiral galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap970419.html ], minding its own business, when NGC 4038 [ http://antwrp.gsfc.nasa.gov/apod/ap970506.html ] crashed into it. The evolving wreckage, known as the "Antennae [ http://galileo.ifa.hawaii.edu/~hibbard/n4038/n4038.html ]", is pictured above. As gravity [ http://loner.ccsr.uiuc.edu/cyberprof/physics/101/Lecture/L13P3.html ] pulls each galaxy apart, clouds of gas slam into each other and bright blue knots are formed. These knots are large clusters of stars imbedded in vast regions of ionized hydrogen gas [ http://www.phys.unm.edu/~duric/l2h/l6/node1.html ]. The high abundance of relatively dim star clusters is quite unlike our Milky Way's globular cluster system [ http://www.limber.org/globs.html ], though. Perhaps some of these young star cluster [ http://antwrp.gsfc.nasa.gov/apod/ap970214.html ]s will go on to form globular clusters [ http://antwrp.gsfc.nasa.gov/apod/ap961004.html ], while others will disperse through close gravitational encounters. The above picture [ http://archive.stsci.edu/cgi-bin/hst_proposal_search?proposal_id=304&action=search&show=data+abs ] is centered around the larger of the two interacting galaxies: NGC 4038. The diagonal streak across the upper left is unrelated to the colliding galaxies. The color contrast [ http://oposite.stsci.edu/pubinfo/LookLike/ ] in the above three-color mosaic was chosen to highlight extended features.
Open Star Clusters M35 and N …
Title Open Star Clusters M35 and NGC 2158
Explanation Open clusters of stars can be near or far, young or old, and diffuse or compact. Open clusters [ http://www.seds.org/messier/open.html ] may contain from 100 to 10,000 stars, all of which formed at nearly the same time. Bright blue stars [ http://antwrp.gsfc.nasa.gov/apod/ap021201.html ] frequently distinguish younger open clusters. M35 [ http://www.seds.org/messier/m/m035.html ], pictured above [ http://www.cfht.hawaii.edu/HawaiianStarlight/AIOM/English/CFHT-Coelum-AIOM.html ] on the upper left, is relatively nearby at 2800 light years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] distant, relatively young at 150 million years old, and relatively diffuse, with about 2500 stars spread out over a volume 30 light years across. An older and more compact open cluster, NGC 2158 [ http://www.seds.org/~spider/spider/MWGC/n2158.html ], is visible above [ http://www.cfht.hawaii.edu/HawaiianStarlight/AIOM/English/CFHT-Coelum-AIOM.html ] on the lower right. NGC 2158 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.332..705C ] is four times more distant that M35 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001ApJ...546.1006B ], over 10 times older, and much more compact as it contains many more stars in roughly the same volume of space. NGC 2158 [ http://antwrp.gsfc.nasa.gov/apod/ap021129.html ]'s bright blue stars have self-destructed [ http://heasarc.gsfc.nasa.gov/docs/snr.html ], leaving cluster light to be dominated by older and yellower star [ http://antwrp.gsfc.nasa.gov/apod/ap000815.html ]s. Both clusters are visible toward the constellation [ http://www.adlerplanetarium.org/history/exhibits/constellations/ ] of Gemini [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Gemini.html ] -- M35 with binoculars and NGC 2158 with a small telescope.
The Stars of NGC 300
Title The Stars of NGC 300
Explanation Like grains of sand [ http://astronomy.swin.edu.au/staff/gmackie/billions.html ] on a cosmic beach, individual stars of large spiral galaxy NGC 300 [ http://heritage.stsci.edu/2004/13/ ] are resolved in this sharp image from the Hubble Space Telescope's Advanced Camera for Surveys (ACS [ http://hubblesite.org/sci.d.tech/nuts_.and._bolts/ instruments/acs/ ]). The inner region of the galaxy is pictured [ http://hubblesite.org/newscenter/newsdesk/archive/releases/ 2004/13/fastfacts/ ], spanning about 7,500 light-years. At its center is the bright, densely packed galactic core surrounded by a loose array of dark dust lanes mixed with the stars in the galactic plane. NGC 300 lies 6.5 million light-years away and is part of a group of galaxies [ http://www.seds.org/messier/xtra/ngc/sclgr.html ] named for the southern constellation Sculptor. Hubble's unique ability to distinguish so many stars [ http://hubblesite.org/newscenter/newsdesk/archive/releases/ 2004/13/ ] in NGC 300 [ http://antwrp.gsfc.nasa.gov/apod/ap020821.html ] can be used to hone techniques [ http://www.ifa.hawaii.edu/%7Ebresolin/Araucaria/ ] for making distance measurements [ http://www.astro.ucla.edu/~wright/ distance.htm ] on extragalactic scales [ http://antwrp.gsfc.nasa.gov/diamond_jubilee/ debate96.html ].
NGC 6823: Cloud Sculpting St …
Title NGC 6823: Cloud Sculpting Star Cluster
Explanation Star cluster NGC 6823 is ready for its close-up. The center of the open cluster, visible [ http://www.cfht.hawaii.edu/HawaiianStarlight/AIOM/English/CFHT-Coelum-AIOM-Oct2004.html ] on the upper right, formed only about two million years ago and is dominated in brightness by a host of bright young blue stars [ http://antwrp.gsfc.nasa.gov/apod/ap031227.html ]. Outer parts of the cluster, visible above [ http://www.cfht.hawaii.edu/HawaiianStarlight/AIOM/English/CFHT-Coelum-AIOM-Oct2004.html ] in the image center as the stars and pillars of emission [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ] nebula NGC 6820 [ http://www.rc-astro.com/nebulae/ngc6820.htm ], contain even younger stars. The huge pillars [ http://antwrp.gsfc.nasa.gov/apod/ap031026.html ] of gas and dust [ http://antwrp.gsfc.nasa.gov/apod/ap030706.html ] likely get their elongated shape by erosion [ http://antwrp.gsfc.nasa.gov/apod/ap031228.html ] from hot radiation emitted from the brightest cluster stars. Striking dark globules [ http://antwrp.gsfc.nasa.gov/apod/ap030816.html ] of gas and dust are also visible across the bottom of this image by the 25 year old [ http://www.cfht.hawaii.edu/News/Anniversary/ ] Canada France Hawaii Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap000905.html ]. Open star cluster NGC 6823 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1988AJ.....96.1389S ] spans about 50 light years and lies about 6000 light years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] away toward the constellation [ http://www.iolaks.com/softech/astro/astro3.htm ] of Vulpecula [ http://www.astronomical.org/portal/modules/wfsection/article.php?articleid=88 ] (The Fox).
NGC 1808: A Nearby Starburst …
Title NGC 1808: A Nearby Starburst Galaxy
Explanation NGC 1808 is a galaxy in turmoil. A barred spiral [ http://antwrp.gsfc.nasa.gov/apod/ap970519.html ] with marked similarities to our home Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap971229.html ], NGC 1808 [ http://www.atnf.csiro.au/~bkoribal/phd_thesis.html ] is distinguished by a peculiar nucleus [ http://antwrp.gsfc.nasa.gov/apod/ap980323.html ], an unusually warped disk [ http://galileo.ifa.hawaii.edu/faculty/barnes/ast626/wdg.html ], and strange flows [ http://www.atnf.csiro.au/~bkoribal/n1808_hi.html ] of hydrogen [ http://cst.lanl.gov/CST/imagemap/periodic/1.html ] gas out from the central regions. Amidst all of this, NGC 1808 is undergoing so much star formation it has been deemed a starburst galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap951016.html ]. In the above color-enhanced photograph [ http://sol.stsci.edu/~mutchler/ngc1808/ngc1808b.html ], regions of active star formation and shown by their blue glow. Here bright blue stars have recently formed and are energizing large clouds of surrounding hydrogen gas. The reddish brown regions indicate dense interstellar dust [ http://astro.gmu.edu/classes/a10695/notes/l08/l08.html ]. NGC 1808 is a relatively close 40 million light-years away, and stretches about 35,000 light-years across. The peculiar state of NGC 1808 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=J76-06426&db_key=AST&high=34f6e1de7f22220 ] may be caused by the gravity of neighboring galaxy NGC 1792 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=A95-71214&db_key=AST&high=34f6e1de7f22233 ].
NGC 6946: The Fireworks Gala …
Title NGC 6946: The Fireworks Galaxy
Explanation Why is this galaxy so active? Nearby spiral galaxy NGC 6946 [ http://www.noao.edu/outreach/aop/observers/n6946.html ] is undergoing a tremendous burst of star formation with no obvious cause. In many cases spirals light up when interacting with another galaxy, but NGC 6946 [ http://antwrp.gsfc.nasa.gov/apod/ap040410.html ] appears relatively isolated in space. Located just 10 million light years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] away toward the constellation [ http://www.fillingthesky.com/id8.html ] of Cepheus [ http://www.astronomical.org/portal/modules/wfsection/article.php?articleid=20 ], this beautiful face-on spiral [ http://antwrp.gsfc.nasa.gov/apod/ap041216.html ] spans about 20,000 light years and is seen through a field of foreground stars from our Milky Way Galaxy [ http://cassfos02.ucsd.edu/public/tutorial/MW.html ]. The center of NGC 6946 [ http://www.gemini.edu/index.php?option=content&task=view&id=116 ] is home to a nuclear starburst itself, and picturesque dark dust is seen lacing the disk along with bright blue stars [ http://antwrp.gsfc.nasa.gov/apod/ap031227.html ], red emission nebulas [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ], fast moving gas clouds, and unusually frequent supernovas [ http://heasarc.gsfc.nasa.gov/docs/snr.html ]. The 8-meter Gemini North Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap990629.html ] in Hawaii, USA [ http://www.cia.gov/cia/publications/factbook/geos/us.html ], took the above image [ http://www.gemini.edu/index.php?set_albumName=Previous-Featured-Images&id=ngc6946_Small&option=com_gallery&Itemid=39&include=view_photo.php ]. A suggested explanation [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000MNRAS.319..821P ] for the high star formation rate is the recent accretion of many primordial low-mass neutral hydrogen clouds [ http://www.universetoday.com/am/publish/clouds_hydrogen_swarm_andromeda.html?422004 ] from the surrounding region.
Stars, Dust and Nebula in NG …
Title Stars, Dust and Nebula in NGC 6559
Explanation When stars form, pandemonium reigns. A textbook [ http://zebu.uoregon.edu/text.html ] case is the star forming region NGC 6559 [ http://antwrp.gsfc.nasa.gov/apod/ap040629.html ]. Visible above are red glowing emission nebulas [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ] of hydrogen [ http://periodic.lanl.gov/elements/1.html ], blue reflection nebulas [ http://en.wikipedia.org/wiki/Reflection_nebula ] of dust [ http://antwrp.gsfc.nasa.gov/apod/ap030706.html ], dark absorption nebulas [ http://www.glyphweb.com/esky/concepts/absorptionnebula.html ] of dust, and the stars that formed from them. The first massive stars formed from the dense gas will emit energetic light [ http://imagers.gsfc.nasa.gov/ems/uv.html ] and winds [ http://www.peripatus.gen.nz/Astronomy/SteWin.html ] that erode, fragment, and sculpt [ http://antwrp.gsfc.nasa.gov/apod/ap050425.html ] their birthplace. And then they explode [ http://heasarc.gsfc.nasa.gov/docs/snr.html ]. The resulting morass [ http://antwrp.gsfc.nasa.gov/apod/ap020424.html ] can be as beautiful as it is complex. After tens of millions of years, the dust boils away, the gas gets swept away, and all that is left is a naked open cluster [ http://antwrp.gsfc.nasa.gov/apod/ap040222.html ] of stars.
The Colliding Galaxies of NG …
Title The Colliding Galaxies of NGC 520
Explanation Is this one galaxy or two? The jumble of stars, gas, and dust [ http://antwrp.gsfc.nasa.gov/apod/ap030706.html ] that is NGC 520 is now thought to incorporate the remains of two separate galaxies. A combination of observations and simulations indicate the NGC 520 [ http://www.kopernik.org/images/archive/n520.htm ] is actually the collision of two disk galaxies. Interesting features of NGC 520 include an unfamiliar looking tail of stars [ http://antwrp.gsfc.nasa.gov/apod/ap040515.html ] at the image bottom and a perhaps more familiar looking band of dust [ http://antwrp.gsfc.nasa.gov/apod/ap031008.html ] running diagonally across the image center. A similar looking collision might be expected were our disk Milky Way Galaxy [ http://www.seds.org/messier/more/mw.html ] to collide [ http://www.cita.utoronto.ca/~dubinski/merger/bigmerger.html ] with our large galactic neighbor Andromeda [ http://antwrp.gsfc.nasa.gov/apod/ap040718.html ] (M31). The collision that defines NGC 520 [ http://www.cv.nrao.edu/~jhibbard/n520/n520.html ] started about 300 million years ago and continues today. Although the speeds of stars are fast, the distances are so vast that the interacting pair will surely not change its shape noticeably during our lifetimes. NGC 520 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005MNRAS.359..455R ], at visual magnitude [ http://en.wikipedia.org/wiki/Apparent_magnitude ] 12, has been noted to be one of the brightest interacting galaxies on the sky, after interacting pairs of galaxies known as the Antennae [ http://antwrp.gsfc.nasa.gov/apod/ap971022.html ]. NGC 520 was imaged above [ http://www.gemini.edu/index.php?option=content&task=view&id=150&Itemid=0&limit=1&limitstart=1 ] in spectacular fashion by the Gemini Observatory [ http://antwrp.gsfc.nasa.gov/apod/ap030909.html ] in Hawaii [ http://en.wikipedia.org/wiki/Hawaii ], USA [ http://www.cia.gov/cia/publications/factbook/geos/us.html ]. Also known as Arp [ http://www.haltonarp.com/ ] 157, NGC 520 lies about 100 million light years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] distant, spans about 100 thousand light years, and can be seen with a small telescope toward the constellation [ http://www.astro.wisc.edu/~dolan/constellations/extra/constellations.html ] of the Fish (Pisces [ http://www.astronomical.org/portal/modules/wfsection/article.php?articleid=66 ]).
NGC 6934 from Gemini North
Title NGC 6934 from Gemini North
Explanation What's going on near the center of globular cluster [ http://antwrp.gsfc.nasa.gov/apod/ap981107.html ] NGC 6934? The blur caused by the Earth's atmosphere [ http://www.aspire.cs.uah.edu/~jonesj/r.html ] has prevented astronomers from discerning individual stars in this unusual environment. Telescopes in space [ http://antwrp.gsfc.nasa.gov/apod/ap970306.html ] can help [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999AJ....117..264P ], but the new Gemini North telescope [ http://antwrp.gsfc.nasa.gov/apod/ap990629.html ] took the above picture [ http://www.gemini.edu/dedication/ngc6934.html ] from the ground. In infrared light [ http://www.ipac.caltech.edu/Outreach/Edu/discovery.html ], Gemini was able to use its adaptive optic mirrors [ http://claret.kpno.noao.edu/wiyn/wttm.html ] to resolve stars even near the globular cluster's center. NGC 6934 [ http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?1973AJ.....78..242H ] is a 15 billion-year-old ball of hundreds of thousands of stars. Dating stars in ancient globular clusters [ http://antwrp.gsfc.nasa.gov/apod/ap990117.html ] like NGC 6934 provide valuable constraints on the minimum age of the universe [ http://www.ess.sunysb.edu/~simswg/siswg/node19.html ].
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