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Andromeda of Milky Way Galaxy and Goddard Space Flight Center (GSFC)
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Amazing Andromeda Galaxy
| Title |
Amazing Andromeda Galaxy |
| Description |
The many "personalities" of our great galactic neighbor, the Andromeda galaxy, are exposed in this new composite image from NASA's Galaxy Evolution Explorer and the Spitzer Space Telescope. The wide, ultraviolet eyes of Galaxy Evolution Explorer reveal Andromeda's "fiery" nature -- hotter regions brimming with young and old stars. In contrast, Spitzer's super-sensitive infrared eyes show Andromeda's relatively "cool" side, which includes embryonic stars hidden in their dusty cocoons. Galaxy Evolution Explorer detected young, hot, high-mass stars, which are represented in blue, while populations of relatively older stars are shown as green dots. The bright yellow spot at the galaxy's center depicts a particularly dense population of old stars. Swaths of red in the galaxy's disk indicate areas where Spitzer found cool, dusty regions where stars are forming. These stars are still shrouded by the cosmic clouds of dust and gas that collapsed to form them. Together, Galaxy Evolution Explorer and Spitzer complete the picture of Andromeda's swirling spiral arms. Hints of pinkish purple depict regions where the galaxy's populations of hot, high-mass stars and cooler, dust-enshrouded stars co-exist. Located 2.5 million light-years away, the Andromeda is our largest nearby galactic neighbor. The galaxy's entire disk spans about 260,000 light-years, which means that a light beam would take 260,000 years to travel from one end of the galaxy to the other. By comparison, our Milky Way galaxy's disk is about 100,000 light-years across. This image is a false color composite comprised of data from Galaxy Evolution Explorer's far-ultraviolet detector (blue), near-ultraviolet detector (green), and Spitzer's multiband imaging photometer at 24 microns (red). |
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Andromeda Island Universe
| Title |
Andromeda Island Universe |
| Explanation |
How far can you see? The most distant object easily visible to the unaided eye is M31 [ http://www.seds.org/messier/xtra/history/m-m31_42.html ], the great Andromeda Galaxy [ http://www.seds.org/messier/m/m031.html ] some two million light-years away. Without a telescope, even this immense spiral galaxy appears as an unremarkable, faint, nebulous cloud in the constellation Andromeda [ http://www.astronomical.org/constellations/and.html ]. But a bright yellow nucleus, dark winding dustlanes, gorgeous blue spiral arms and star clusters are recorded in this stunning telescopic digital [ http://www.geocities.com/CapeCanaveral/Hall/6432/ homepage.html ] mosaic of the nearby island universe. While even casual skygazers [ http://badastronomy.com/bitesize/galaxies.html ] are now inspired by the knowledge that there are many [ http://antwrp.gsfc.nasa.gov/apod/ap000709.html ] distant galaxies like M31, astronomers seriously debated [ http://adsbit.harvard.edu/cgi-bin/ nph-iarticle_query?1995PASP%2E%2E107%2E1133T ] this fundamental concept only 80 years ago. Were these "spiral nebulae" simply outlying components of our own Milky Way Galaxy or were they instead "island universes" -- distant systems of stars comparable to the Milky Way itself? This question was central to the famous Shapley-Curtis [ http://antwrp.gsfc.nasa.gov/diamond_jubilee/ debate20.html ] debate [ http://antwrp.gsfc.nasa.gov/diamond_jubilee/debate.html ] of 1920, which was later resolved by observations [ http://antwrp.gsfc.nasa.gov/apod/ap960406.html ] of M31 in favor of Andromeda, island universe [ http://www.astr.ua.edu/goodies/data_resources/galaxies.text ]. |
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M31: The Andromeda Galaxy
| Title |
M31: The Andromeda Galaxy |
| Explanation |
Andromeda is the nearest major galaxy [ http://www.seds.org/messier/galaxy.html] to our own Milky Way Galaxy [ http://cassfos02.ucsd.edu/public/tutorial/MW.html ]. Our Galaxy is thought to look much like Andromeda [ http://antwrp.gsfc.nasa.gov/apod/ap020518.html ]. Together these two galaxies dominate the Local Group [ http://www.seds.org/messier/more/local.html ] of galaxies. The diffuse light from Andromeda [ http://www.seds.org/messier/m/m031.html ] is caused by the hundreds of billions of stars [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#star ] that compose it. The several distinct stars that surround Andromeda [ http://antwrp.gsfc.nasa.gov/apod/ap010917.html ]'s image are actually stars in our Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap000518.html ] that are well in front of the background object. Andromeda [ http://www.noao.edu/image_gallery/html/im0424.html ] is frequently referred to as M31 since it is the 31st object [ http://antwrp.gsfc.nasa.gov/apod/ap960626.html ] on Messier [ http://www.seds.org/messier/xtra/history/biograph.html ]'s list of diffuse sky objects. M31 [ http://antwrp.gsfc.nasa.gov/apod/ap020412.html ] is so distant it takes about two million years for light to reach us from there. Although visible without aid, the above image [ http://www.robgendlerastropics.com/M31Page.html ] of M31 is a digital mosaic of 20 frames taken with a small telescope. Much about M31 remains unknown [ http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1995ApJ...444..157A ], including how the center acquired two nuclei [ http://antwrp.gsfc.nasa.gov/apod/ap961011.html ]. |
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Dwarf Elliptical Galaxy NGC
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| 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 ]. |
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Southwest Andromeda
| Title |
Southwest Andromeda |
| Explanation |
This new image composite [ http://www.subaru.naoj.org/Latestnews/200109/M31/index.html ] of the southwest region of M31 [ http://antwrp.gsfc.nasa.gov/apod/ap991114.html ] from the Subaru Telescope [ http://www.subaru.naoj.org/Introduction/outline.html ] shows many stars, nebulae, and star clusters never before resolved. An older population of stars near Andromeda's center [ http://antwrp.gsfc.nasa.gov/apod/ap961011.html ] causes the yellow hue visible on the upper right. Young blue stars stand out in the spiral arms [ http://fuse.pha.jhu.edu/~danforth/spiral/ ] on the lower left. Red emission nebula [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ], blue open clusters [ http://antwrp.gsfc.nasa.gov/apod/open_clusters.html ] of stars, and sweeping lanes of dark dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ] punctuate the swirling giant. Andromeda [ http://www.seds.org/messier/m/m031.html ], at about 2.5 million light years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] distant, and our Milky Way [ http://antwrp.gsfc.nasa.gov/apod/milky_way.html ] are the largest galaxies [ http://www.seds.org/messier/galaxy.html ] in the Local Group of Galaxies [ http://www.seds.org/messier/more/local.html ]. Understanding M31 [ http://antwrp.gsfc.nasa.gov/apod/ap000908.html ] helps astronomers to understand our own Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap000130.html ], since the two are so similar. |
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Elements of Nearby Spiral M3
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| Title |
Elements of Nearby Spiral M33 |
| Explanation |
Spiral galaxy [ http://www.seds.org/messier/spir.html ] M33 is a mid-sized member of our Local Group of Galaxies [ http://www.seds.org/messier/more/local.html ]. M33 [ http://antwrp.gsfc.nasa.gov/apod/ap980721.html ] is also called the Triangulum Galaxy [ http://www.seds.org/messier/m/m033.html ] for the constellation [ http://www.astronomical.org/constellations/tri.html ] in which it resides. About four times smaller (in radius) than our Milky Way Galaxy [ http://www.star.le.ac.uk/edu/mway/ ] and the Andromeda Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap991114.html ] (M31), it is much larger than the many of the local dwarf spheroidal [ http://antwrp.gsfc.nasa.gov/apod/ap991003.html ] galaxies. M33 [ http://antwrp.gsfc.nasa.gov/apod/ap960708.html ]'s proximity to M31 [ http://antwrp.gsfc.nasa.gov/apod/ap010917.html ] causes it to be thought by some to be a satellite galaxy of this more massive galaxy. M33 [ http://sirtf.caltech.edu/Education/Messier/m33.html ]'s proximity to our Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/milky_way.html ] causes it to appear more than twice the angular size of the Full Moon [ http://antwrp.gsfc.nasa.gov/apod/ap010218.html ], and be visible with a good pair of binoculars. The above high-resolution image [ http://www.lowell.edu/users/massey/lgsurvey.html ] highlights light emitted by hydrogen [ http://periodic.lanl.gov/elements/1.html ] in red and oxygen [ http://periodic.lanl.gov/elements/8.html ] in blue. It was taken to help separate stars from emission nebulae [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ], and therefore help study [ http://www.aas.org/publications/baas/v32n4/aas197/743.htm ] how galaxies form stars. |
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Andromeda Island Universe
| Title |
Andromeda Island Universe |
| Explanation |
The most distant object easily visible to the unaided eye is M31 [ http://www.seds.org/messier/xtra/history/m-m31_42.html ], the great Andromeda Galaxy [ http://www.seds.org/messier/m/m031.html ] some two and a half million light-years away. But without a telescope, even this immense spiral galaxy - spanning over [ http://antwrp.gsfc.nasa.gov/apod/ap061228.html ] 200,000 light years - appears as a faint, nebulous cloud in the constellation Andromeda [ http://www.hawastsoc.org/deepsky/and/index.html ]. In contrast, a bright yellow nucleus, dark winding dust lanes, gorgeous blue spiral arms and star clusters are recorded in this stunning telescopic digital mosaic [ http://astrophoto.com/M31.htm ]. While even casual skygazers [ http://badastronomy.com/bitesize/galaxies.html ] are now inspired by the knowledge that there are many [ http://antwrp.gsfc.nasa.gov/apod/ap070208.html ] distant galaxies like M31, astronomers seriously debated [ http://adsbit.harvard.edu/cgi-bin/ nph-iarticle_query?1995PASP%2E%2E107%2E1133T ] this fundamental concept less than 90 years ago. Were these "spiral nebulae" simply outlying components of our own Milky Way Galaxy or were they instead "island universes" -- distant systems of stars comparable to the Milky Way itself? This question was central to the famous Shapley-Curtis [ http://antwrp.gsfc.nasa.gov/diamond_jubilee/ debate20.html ] debate [ http://antwrp.gsfc.nasa.gov/diamond_jubilee/debate.html ] of 1920, which was later resolved by observations [ http://antwrp.gsfc.nasa.gov/apod/ap960406.html ] of M31 in favor of Andromeda, island universe [ http://www.astr.ua.edu/goodies/data_resources/galaxies.text ]. |
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Andromeda Island Universe
| Title |
Andromeda Island Universe |
| Explanation |
How far can you see? The most distant object easily visible to the unaided eye is M31 [ http://www.seds.org/messier/xtra/history/m-m31_42.html ], the great Andromeda Galaxy [ http://www.seds.org/messier/m/m031.html ] some two million light-years away. Without a telescope, even this immense spiral galaxy appears as an unremarkable, faint, nebulous cloud in the constellation Andromeda [ http://www.astronomical.org/constellations/and.html ]. But a bright yellow nucleus, dark winding dust lanes, gorgeous blue spiral arms and star clusters are recorded in this stunning telescopic digital [ http://www.robgendlerastropics.com/index.html ] mosaic of the nearby island universe. While even casual skygazers [ http://badastronomy.com/bitesize/galaxies.html ] are now inspired by the knowledge that there are many [ http://antwrp.gsfc.nasa.gov/apod/ap000709.html ] distant galaxies like M31, astronomers seriously debated [ http://adsbit.harvard.edu/cgi-bin/ nph-iarticle_query?1995PASP%2E%2E107%2E1133T ] this fundamental concept only 80 years ago. Were these "spiral nebulae" simply outlying components of our own Milky Way Galaxy or were they instead "island universes" -- distant systems of stars comparable to the Milky Way itself? This question was central to the famous Shapley-Curtis [ http://antwrp.gsfc.nasa.gov/diamond_jubilee/ debate20.html ] debate [ http://antwrp.gsfc.nasa.gov/diamond_jubilee/debate.html ] of 1920, which was later resolved by observations [ http://antwrp.gsfc.nasa.gov/apod/ap960406.html ] of M31 in favor of Andromeda, island universe [ http://www.astr.ua.edu/goodies/data_resources/galaxies.text ]. |
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Local Group Galaxy NGC 205
| Title |
Local Group Galaxy NGC 205 |
| Explanation |
The Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap950908.html ] is not alone. It is part of a gathering of about 25 galaxies known as the Local Group [ http://www.csc.fi/jpr/galaxy/lbang.html ]. Members include the Great Andromeda Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap950724.html ] (M31), M32 [ http://antwrp.gsfc.nasa.gov/apod/ap960106.html ], M33 [ http://seds.lpl.arizona.edu/messier/m/m033.html ], the Large Magellanic Clouds [ http://antwrp.gsfc.nasa.gov/apod/ap950918.html ], the Small Magellanic Clouds [ http://antwrp.gsfc.nasa.gov/apod/ap950919.html ], Dwingeloo 1 [ http://antwrp.gsfc.nasa.gov/apod/ap951017.html ], several small irregular galaxies [ http://antwrp.gsfc.nasa.gov/apod/ap950728.html ], and many dwarf elliptical galaxies [ http://www.physics.mcmaster.ca/Grads/PRD2.html ]. Pictured is one of the many dwarf ellipticals: NGC 205. Like M32, NGC 205 is a companion to the large M31, and can sometimes be seen to the south of M31 [ http://seds.lpl.arizona.edu/messier/m/m031.html ]'s center in photographs. The above image [ http://crux.astr.ua.edu/gifimages/m110r.html ] shows this galaxy to be unusual for an elliptical galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap950913.html ] in that it contains at least two dust clouds [ http://antwrp.gsfc.nasa.gov/apod/ap951107.html ] (at 7 and 11 o'clock - they are visible but hard to spot) and signs of recent star formation. This galaxy is sometimes known as M110, although it was actually not part of Messier [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#messier ]'s original catalog. |
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Dwarf Elliptical Galaxy M32
| Title |
Dwarf Elliptical Galaxy M32 |
| Explanation |
Being the largest galaxy around can sometimes make you popular. Pictured is M31's companion galaxy M32 [ http://crux.astr.ua.edu/gifimages/m32.html ]. M31 [ http://antwrp.gsfc.nasa.gov/apod/ap950724.html ], the Andromeda galaxy, is the largest galaxy in our Local Group [ http://www.csc.fi/jpr/galaxy/lbang.html ] of galaxies - even our tremendous Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap950908.html ] is smaller. Little M32 is visible in most pictures of M31 - it is the small circular spot north of M31's center. M32 is a dwarf elliptical galaxy [ http://www.physics.mcmaster.ca/Grads/PRD2.html ]. Elliptical galaxies [ http://sousun1.phys.soton.ac.uk/PH308/galaxies/ellipticals.html ] have little or no measurable gas [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#hydrogen ] or dust [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#dust ] - they are composed completely of stars [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#star ] and typically appear more red than spiral galaxies [ http://antwrp.gsfc.nasa.gov/apod/ap951218.html ]. Elliptical galaxies [ http://antwrp.gsfc.nasa.gov/apod/ap950913.html ] do not have disks - they generally have oblong shapes and therefore show elliptical profiles on the sky. |
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Nearby Spiral Galaxy NGC 494
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| Title |
Nearby Spiral Galaxy NGC 4945 |
| Explanation |
For such a close galaxy, NGC 4945 is easy to miss. NGC 4945 [ http://www.ast.cam.ac.uk/AAO/images/captions/aat101.html ] is a spiral galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap980525.html ] in the Centaurus Group of galaxies, located only six times farther away than the prominent Andromeda Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap991114.html ]. The thin disk galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap020703.html ] is oriented nearly edge-on, however, and shrouded in dark dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ]. Therefore galaxy-gazers searching the southern constellation of Centaurus [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Centaurus.html ] need a telescope to see it. The above picture [ http://www.eso.org/outreach/press-rel/pr-1999/phot-18-99.html ] was taken with a large telescope [ http://www.ls.eso.org/lasilla/Telescopes/2p2T/E2p2M/ ] testing a new wide-angle, high-resolution CCD camera [ http://www.ls.eso.org/lasilla/Telescopes/2p2T/E2p2M/WFI/ ]. Most of the spots scattered about the frame [ http://www.eso.org/outreach/epr/posters/ ] are foreground stars in our own Galaxy [ http://antwrp.gsfc.nasa.gov/apod/milky_way.html ], but some spots are globular clusters [ http://antwrp.gsfc.nasa.gov/apod/globular_clusters.html ] orbiting the distant galaxy. NGC 4945 [ http://astro.ph.unimelb.edu.au/central/images/mbrown/ngc4945.html ] is thought to be quite similar to our own Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap971229.html ]. X-ray [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html ] observations reveal, however, that NGC 4945 has an unusual, energetic, Seyfert [ http://antwrp.gsfc.nasa.gov/apod/ap010701.html ] 2 nucleus that might house a large black hole [ http://antwrp.gsfc.nasa.gov/apod/ap960911.html ]. |
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Island Universe, Cosmic Sand
| Title |
Island Universe, Cosmic Sand |
| Explanation |
On August 13, while counting Perseid meteors [ http://comets.amsmeteors.org/meteors/showers/ perseids.html ] under dark [ http://www.darksky.org/ida/darksky/ index.html ], early morning Arizona skies, Rick Scott set out to photograph [ http://members.cox.net/rmscott/ gallery_space_sky02.html ] their fleeting but fiery trails. The equipment he used included a telephoto lens and fast color film. After 21 pictures he'd caught only two meteors, but luckily this was one of them. Tracking the sky, his ten minute long exposure shows a field of many stars in our own Milky Way galaxy [ http://www.seds.org/messier/ more/mw.html ], most too faint to be seen by the unaided eye. Flashing [ http://antwrp.gsfc.nasa.gov/apod/ap990219.html ] from lower left to upper right, the bright meteor would have been an easy eyeful though, as friction with Earth's atmosphere vaporized [ http://antwrp.gsfc.nasa.gov/apod/ap020816.html ] the hurtling grain of cosmic sand [ http://antwrp.gsfc.nasa.gov/apod/ap001117.html ], a piece of dust from Comet Swift-Tuttle [ http://comets.amsmeteors.org/comets/pcomets/ 109p.html ]. Just above and left of center, well beyond the stars of the Milky Way, lies the island universe [ http://antwrp.gsfc.nasa.gov/apod/ap020518.html ] known as M31 or the Andromeda galaxy. The visible meteor trail begins about 100 kilometers above Earth's surface, one of the closest celestial objects seen in the sky. In contrast, Andromeda [ http://www.seds.org/messier/m/ m031.html ], about 2 million light-years away, is the most distant object easily visible to the naked-eye. |
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Nearby Spiral M33
| Title |
Nearby Spiral M33 |
| Explanation |
Spiral galaxy [ http://www.seds.org/messier/spir.html ] M33 is a mid-sized member of our Local Group of Galaxies [ http://www.seds.org/messier/more/local.html ]. M33 [ http://antwrp.gsfc.nasa.gov/apod/ap980721.html ] is also called the Triangulum Galaxy [ http://www.seds.org/messier/m/m033.html ] for the constellation [ http://www.astronomical.org/constellations/tri.html ] in which it resides. About four times smaller (in radius) than our Milky Way Galaxy [ http://www.star.le.ac.uk/edu/mway/ ] and the Andromeda Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap021021.html ] (M31), it is much larger than the many of the local dwarf spheroidal [ http://antwrp.gsfc.nasa.gov/apod/ap991003.html ] galaxies. M33 [ http://antwrp.gsfc.nasa.gov/apod/ap960708.html ]'s proximity to M31 [ http://antwrp.gsfc.nasa.gov/apod/ap010917.html ] causes it to be thought by some to be a satellite galaxy of this more massive galaxy. M33 [ http://sirtf.caltech.edu/Education/Messier/m33.html ]'s proximity to our Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/milky_way.html ] causes it to appear more than twice the angular size of the Full Moon [ http://antwrp.gsfc.nasa.gov/apod/ap010218.html ], and be visible with a good pair of binoculars. The above high-resolution image [ http://www.noao.edu/image_gallery/html/im0775.html ] from the 0.90-m telescope [ http://www.noao.edu/0.9m/manual.html ] at Kitt Peak National Observatory [ http://www.noao.edu/kpno/ ] is a four-color composite. |
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M33: The Triangulum Galaxy
| Title |
M33: The Triangulum Galaxy |
| Explanation |
The spiral galaxy [ http://www.astro.rug.nl/~jansen/www/articles/spectrum/spectrum.html ] M33 [ http://ftp.seds.org/messier/m/m033.html] is a mid-sized member of our Local Group of galaxies [ http://antwrp.gsfc.nasa.gov/apod/lib/local_group.html ]. M33 is also called the Triangulum Galaxy for the constellation [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Triangulum.html ] in which it resides. About four times smaller (in radius) than our Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap960213.html ] and the Andromeda Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap950724.html ] (M31), it is much larger than the many of the local dwarf spheroidal galaxies [ http://antwrp.gsfc.nasa.gov/apod/ap960519.html ]. M33's proximity to M31 causes it to be thought by some to be a satellite galaxy of this more massive galaxy. M33's proximity to our Milky Way galaxy causes it to appear more than twice the angular size of the full moon [ http://antwrp.gsfc.nasa.gov/apod/ap950821.html ], and visible with a good pair of binoculars [ http://jersey.uoregon.edu/~bdany/optics.html ]. In the above picture [ http://fondue.gsfc.nasa.gov/UIT/Astro1/Astro1_pictures.html ], visible light is shown in red and ultraviolet light superposed in blue [ http://antwrp.gsfc.nasa.gov/apod/ap960409.html ]. Stars in M33 are the most distant ever to be studied spectroscopically [ http://www.aas.org/ApJ/v455n2/5526/sc0.html ]. |
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The Aquarius Dwarf
| Title |
The Aquarius Dwarf |
| 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 50 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/ap021021.html ] (M31), M32 [ http://antwrp.gsfc.nasa.gov/apod/ap991103.html ], M33 [ http://antwrp.gsfc.nasa.gov/apod/ap021202.html ], the Large Magellanic Cloud [ http://antwrp.gsfc.nasa.gov/apod/ap010804.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 above is the Aquarius Dwarf [ http://www.seds.org/~spider/spider/LG/aqr_dw.html ], a faint dwarf irregular galaxy over 3 million light years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] away. An earlier [ http://antwrp.gsfc.nasa.gov/apod/ap970329.html ] APOD [ http://antwrp.gsfc.nasa.gov/apod/ap960204.html ] erroneously identified [ http://www.solstation.com/x-objects/sag-deg.htm ] the above image as the Sagittarius Dwarf [ http://www.seds.org/messier/more/sagdeg.html ]. |
|
Island Universe, Cosmic Sand
| Title |
Island Universe, Cosmic Sand |
| Explanation |
On August 13, 2002, while counting Perseid meteors [ http://science.nasa.gov/headlines/y2003/ 17jul_perseids2003.htm ] under dark [ http://www.darksky.org/ida/darksky/ index.html ], early morning Arizona skies, Rick Scott set out to photograph [ http://members.cox.net/rmscott/ gallery_space_sky02.html ] their fleeting but fiery trails. The equipment he used included a telephoto lens and fast color film. After 21 pictures he'd caught only two meteors, but luckily this was one of them. Tracking the sky, his ten minute long exposure shows a field of many stars in our own Milky Way galaxy [ http://www.seds.org/messier/ more/mw.html ], most too faint to be seen by the unaided eye. Flashing [ http://antwrp.gsfc.nasa.gov/apod/ap990219.html ] from lower left to upper right, the bright meteor would have been an easy eyeful though, as friction with Earth's atmosphere vaporized [ http://antwrp.gsfc.nasa.gov/apod/ap020816.html ] the hurtling grain of cosmic sand [ http://antwrp.gsfc.nasa.gov/apod/ap001117.html ], a piece of dust from Comet Swift-Tuttle [ http://comets.amsmeteors.org/comets/pcomets/ 109p.html ]. Just above and left of center, well beyond the stars of the Milky Way, lies the island universe [ http://antwrp.gsfc.nasa.gov/apod/ap020518.html ] known as M31 or the Andromeda galaxy. The visible meteor trail begins about 100 kilometers above Earth's surface, one of the closest celestial objects seen in the sky. In contrast, Andromeda [ http://www.seds.org/messier/m/ m031.html ], about 2 million light-years away, is the most distant object easily visible to the naked-eye. |
|
The Northern Milky Way
| Title |
The Northern Milky Way |
| Explanation |
Many of the stars in our home Milky Way Galaxy [ http://www.seds.org/messier/more/mw.html ] appear together as a dim band on the sky that passes nearly over the Earth's north [ http://antwrp.gsfc.nasa.gov/apod/ap020818.html ] and south poles. Pictured above [ http://www.astropix.com/HTML/SHOWCASE/NMW.HTM ] is the part of our Galaxy [ http://antwrp.gsfc.nasa.gov/apod/milky_way.html ] that passes closest over the north pole [ http://antwrp.gsfc.nasa.gov/apod/ap000715.html ]. Placing your cursor [ http://www.hyperdictionary.com/dictionary/cursor] over the image will bring up the names of several constellations [ http://www.adlerplanetarium.org/history/exhibits/constellations/timeline.html ] and bright stars [ http://www.astro.wisc.edu/~dolan/constellations/extra/brightest.html ]. The diffuse white Galaxy glow is created by billions of stars, while red patches are large emission nebulas [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ], usually marking areas where bright stars have recently formed. In the north, all of the lights visible at night and all lights that created this image were emitted within the past few thousand years from within the Milky Way Galaxy -- except one. On the upper right is a small faint patch designated M31, the Andromeda Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap021021.html ]. M31 is a spiral galaxy [ http://www.seds.org/messier/spir.html ] similar to our Milky Way [ http://antwrp.gsfc.nasa.gov/apod/ap990224.html ] but so distant it emits the oldest light distinguishable by the unaided eye -- light that takes over two million years to reach us. |
|
The Andromeda Galaxy from GA
…
| Title |
The Andromeda Galaxy from GALEX |
| Explanation |
Why does the Andromeda Galaxy have a giant ring? Viewed in ultraviolet light [ http://imagers.gsfc.nasa.gov/ems/uv.html ], the closest major galaxy to our Milky Way Galaxy [ http://www.seds.org/messier/more/mw.html ] looks more like a ring galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap020909.html ] than a spiral [ http://antwrp.gsfc.nasa.gov/apod/ap030911.html ]. The ring is highlighted beautifully in this newly released image mosaic of Andromeda [ http://antwrp.gsfc.nasa.gov/apod/ap021021.html ] (M31) taken by the GALaxy Evolution Explorer [ http://www.galex.caltech.edu/ABOUT/about.html ] (GALEX), a satellite launched into Earth orbit in April. In the above image [ http://www.galex.caltech.edu/popups/gallery-M31.html ], ultraviolet colors have been digitally shifted to the visual. Young blue stars [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1964ApJS....9...65V ] dominate the image, indicating the star forming ring [ http://antwrp.gsfc.nasa.gov/apod/ap010612.html ] as well as other star forming regions even further from the galactic center [ http://antwrp.gsfc.nasa.gov/apod/ap000121.html ]. The origin of the huge 150,000-light year [ http://chandra.harvard.edu/photo/cosmic_distance.html ] ring is unknown but likely related to gravitational interactions [ http://antwrp.gsfc.nasa.gov/apod/ap020506.html ] with small satellite galaxies [ http://antwrp.gsfc.nasa.gov/apod/ap021202.html ] that orbit near the galactic giant. M31 [ http://www.seds.org/messier/m/m031.html ] lies about three million light-years distant and is bright enough to be seen without binoculars toward the constellation [ http://en2.wikipedia.org/wiki/Constellations ] of Andromeda [ http://www.astronomical.org/constellations/and.html ]. |
|
M31: The Andromeda Galaxy
| Title |
M31: The Andromeda Galaxy |
| Explanation |
Andromeda is the nearest major galaxy to our own Milky Way Galaxy. Our Galaxy is thought to look much like Andromeda. Together these two galaxies dominate the Local Group of galaxies. The diffuse light from Andromeda is caused by the hundreds of billions of stars that compose it. The several distinct stars that surround Andromeda's image are actually stars in our Galaxy that are well in front of the background object. Andromeda is frequently referred to as M31 since it is the 31st object [ http://antwrp.gsfc.nasa.gov/apod/ap960626.html ] on Messier's [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#messier ] list of diffuse sky objects. M31 is so distant it takes about 2 million years for light to reach us from there. Much about M31 remains unknown, including why the center contains two nuclei. |
|
M31: The Andromeda Galaxy
| Title |
M31: The Andromeda Galaxy |
| Explanation |
Andromeda is the nearest major galaxy [ http://www.seds.org/messier/galaxy.html ] to our own Milky Way Galaxy [ http://cassfos02.ucsd.edu/public/tutorial/MW.html ]. Our Galaxy is thought to look much like Andromeda [ http://antwrp.gsfc.nasa.gov/apod/ap020518.html ]. Together these two galaxies dominate the Local Group [ http://www.seds.org/messier/more/local.html ] of galaxies. The diffuse light from Andromeda [ http://www.seds.org/messier/m/m031.html ] is caused by the hundreds of billions of stars [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#star ] that compose it. The several distinct stars that surround Andromeda [ http://antwrp.gsfc.nasa.gov/apod/ap010917.html ]'s image are actually stars in our Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap000518.html ] that are well in front of the background object. Andromeda [ http://www.noao.edu/image_gallery/html/im0424.html ] is frequently referred to as M31 since it is the 31st object [ http://antwrp.gsfc.nasa.gov/apod/ap960626.html ] on Messier [ http://www.seds.org/messier/xtra/history/biograph.html ]'s list of diffuse sky objects. M31 [ http://antwrp.gsfc.nasa.gov/apod/ap020412.html ] is so distant it takes about two million years for light to reach us from there. Although visible without aid, the above image [ http://www.robgendlerastropics.com/M31Page.html ] of M31 is a digital mosaic of 20 frames taken with a small telescope. Much about M31 remains unknown [ http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1995ApJ...444..157A ], including how the center acquired two nuclei [ http://antwrp.gsfc.nasa.gov/apod/ap961011.html ]. |
|
Andromeda's Core
| Title |
Andromeda's Core |
| Explanation |
The center of the Andromeda galaxy is beautiful but strange. Andromeda [ http://antwrp.gsfc.nasa.gov/apod/ap040718.html ], indexed as M31, is so close to our own Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/milky_way.html ] that it gives a unique perspective into galaxy composition by allowing us to see into its core. Billions of stars swarm around a center that has two nuclei [ http://antwrp.gsfc.nasa.gov/apod/ap961011.html ] and likely houses a supermassive black hole [ http://antwrp.gsfc.nasa.gov/apod/ap040908.html ] over 5 million times the mass of our Sun [ http://www.nineplanets.org/sol.html ]. M31 is about two million light years away and visible with the unaided eye towards the constellation [ http://www.astronomical.org/portal/modules/wfsection/article.php?articleid=1 ] of Andromeda, the princess [ http://www.windows.ucar.edu/tour/link=/the_universe/Constellations/andromeda.html ]. Pictured above [ http://www.robgendlerastropics.com/Andromedacore.html ], dark knots [ http://en.wikipedia.org/wiki/Knots ] of dust [ http://antwrp.gsfc.nasa.gov/apod/ap030706.html ] are seen superposed on the inner 10,000 light years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] of M31's core. The brighter stars are foreground stars located in our Milky Way Galaxy [ http://cassfos02.ucsd.edu/public/tutorial/MW.html ]. |
|
Nearby Spiral M33
| Title |
Nearby Spiral M33 |
| Explanation |
Spiral galaxy [ http://www.seds.org/messier/spir.html ] M33 is a mid-sized member of our Local Group of Galaxies [ http://www.seds.org/messier/more/local.html ]. M33 [ http://antwrp.gsfc.nasa.gov/apod/ap030924.html ] is also called the Triangulum Galaxy [ http://www.seds.org/messier/m/m033.html ] for the constellation [ http://www.astro.wisc.edu/~dolan/constellations/extra/constellations.html ] in which it resides. About four times smaller (in radius) than our Milky Way Galaxy [ http://www.star.le.ac.uk/edu/mway/ ] and the Andromeda Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap040718.html ] (M31), it is much larger than the many of the local dwarf spheroidal [ http://antwrp.gsfc.nasa.gov/apod/ap991003.html ] galaxies. M33 [ http://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search?m33 ]'s proximity to M31 [ http://antwrp.gsfc.nasa.gov/apod/ap010917.html ] causes it to be thought by some to be a satellite galaxy of this more massive galaxy. M33 [ http://coolcosmos.ipac.caltech.edu/cosmic_classroom/multiwavelength_astronomy/multiwavelength_museum/m33.html ]'s proximity to our Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/milky_way.html ] causes it to appear more than twice the angular size of the Full Moon [ http://antwrp.gsfc.nasa.gov/apod/ap040829.html ], and be visible with a good pair of binoculars. |
|
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. |
|
Nearby Spiral Galaxy NGC 494
…
| Title |
Nearby Spiral Galaxy NGC 4945 |
| Explanation |
For such a close galaxy, NGC 4945 is easy to miss. NGC 4945 [ http://www.aao.gov.au/local/www/dfm/aat101.html ] is a spiral galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap980525.html ] in the Centaurus Group of galaxies, located only six times farther away than the prominent Andromeda Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap971101.html ]. The thin disk galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap981220.html ] is oriented nearly edge-on, however, and shrouded in dark dust [ http://antwrp.gsfc.nasa.gov/apod/ap980104.html ]. Therefore galaxy-gazers searching the southern constellation of Centaurus [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Centaurus.html ] need a telescope to see it. The above picture [ http://www.eso.org/outreach/press-rel/pr-1999/phot-18-99.html ] was taken with a large telescope [ http://www.ls.eso.org/lasilla/Telescopes/2p2T/E2p2M/E2p2M.html ] testing a new wide-angle, high-resolution CCD camera [ http://www.ls.eso.org/lasilla/Telescopes/2p2T/E2p2M/WFI/WFI.html ]. Most of the spots scattered about the frame are foreground stars in our own Galaxy, but some spots are globular clusters [ http://antwrp.gsfc.nasa.gov/apod/ap980719.html ] orbiting the distant galaxy. NGC 4945 [ http://astro.ph.unimelb.edu.au/central/images/mbrown/ngc4945.html ] is thought to be quite similar to our own Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap971229.html ]. X-ray [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html ] observations reveal, however, that NGC 4945 has an unusual, energetic, Seyfert [ http://antwrp.gsfc.nasa.gov/apod/ap981023.html ] 2 nucleus that might house a large black hole [ http://antwrp.gsfc.nasa.gov/apod/ap960911.html ]. |
|
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 ]). |
|
The Andromeda Galaxy in Infr
…
| Title |
The Andromeda Galaxy in Infrared |
| Explanation |
What is the Andromeda galaxy really like? To find out, astronomers looked at our largest galactic neighbor [ http://www.seds.org/messier/m/m031.html ] in a different light: infrared [ http://en.wikipedia.org/wiki/Infrared ]. Astronomers [ http://www.aas.org/education/publications/careerbrochure.html ] trained the orbiting Spitzer Space Telescope [ http://ssc.spitzer.caltech.edu/geninfo/ ] at the Messier [ http://antwrp.gsfc.nasa.gov/apod/ap000311.html ] monster (M31) for over 18 hours, creating a mosaic that incorporated 11,000 separate exposures. The result, pictured above [ http://www.spitzer.caltech.edu/Media/releases/ssc2005-20/release.shtml ], shows M31 in greater infrared detail than ever before. Infrared light in this 24-micron color band is particularly sensitive to dust [ http://antwrp.gsfc.nasa.gov/apod/ap030706.html ] heated up by stars. Visible above are previously undiscovered features [ http://uanews.org/cgi-bin/WebObjects/UANews.woa/1/wa/SRStoryDetails?ArticleID=11798 ] including intricate structure in the spiral arms, a spiral arc near the center, an off center ring of star formation, and an unusual hole in the galaxy's disk. In contrast, the Andromeda galaxy appears much smoother in visible light [ http://antwrp.gsfc.nasa.gov/apod/ap040718.html ] and even ultraviolet light [ http://antwrp.gsfc.nasa.gov/apod/ap031222.html ]. Analyses and comparison of this image to other images will likely yield clues not only to the violent past of M31 [ http://antwrp.gsfc.nasa.gov/apod/ap041227.html ] but to our own Milky Way Galaxy [ http://cassfos02.ucsd.edu/public/tutorial/MW.html ] as well. |
|
Andromeda Island Universe
| Title |
Andromeda Island Universe |
| Explanation |
The most distant object easily visible to the unaided eye is M31 [ http://www.seds.org/messier/xtra/history/m-m31_42.html ], the great Andromeda Galaxy [ http://www.seds.org/messier/m/m031.html ] some two million light-years away. But without a telescope, even this immense spiral galaxy - spanning over 200,000 light years - appears as a faint, nebulous cloud in the constellation Andromeda [ http://www.hawastsoc.org/deepsky/and/index.html ]. In contrast, a bright yellow nucleus, dark winding dust lanes, gorgeous blue spiral arms and star clusters are recorded in this stunning telescopic digital mosaic [ http://www.robgendlerastropics.com/M31NMmosaic.html ] with a cumulative exposure of over 90 hours. While even casual skygazers [ http://badastronomy.com/bitesize/galaxies.html ] are now inspired by the knowledge that there are many [ http://antwrp.gsfc.nasa.gov/apod/ap000709.html ] distant galaxies like M31, astronomers seriously debated [ http://adsbit.harvard.edu/cgi-bin/ nph-iarticle_query?1995PASP%2E%2E107%2E1133T ] this fundamental concept only 80 years ago. Were these "spiral nebulae" simply outlying components of our own Milky Way Galaxy or were they instead "island universes" -- distant systems of stars comparable to the Milky Way itself? This question was central to the famous Shapley-Curtis [ http://antwrp.gsfc.nasa.gov/diamond_jubilee/ debate20.html ] debate [ http://antwrp.gsfc.nasa.gov/diamond_jubilee/debate.html ] of 1920, which was later resolved by observations [ http://antwrp.gsfc.nasa.gov/apod/ap960406.html ] of M31 in favor of Andromeda, island universe [ http://www.astr.ua.edu/goodies/data_resources/galaxies.text ]. |
|
M31: The Andromeda Galaxy
| Title |
M31: The Andromeda Galaxy |
| Explanation |
Andromeda is the nearest major galaxy to our own Milky Way Galaxy. Our Galaxy is thought to look much like Andromeda. Together these two galaxies dominate the Local Group of galaxies. The diffuse light from Andromeda is caused by the hundreds of billions of stars that compose it. The several distinct stars that surround Andromeda's image are actually stars in our Galaxy that are well in front of the background object. Andromeda is frequently referred to as M31 since it is the 31st object [ http://antwrp.gsfc.nasa.gov/apod/ap960626.html ] on Messier's [ http://antwrp.gsfc.nasa.gov/apod/ap960626.html ] list of diffuse sky objects. M31 is so distant it takes about two million years for light to reach us from there. Much about M31 remains unknown, including why the center contains two nuclei. |
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