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M4: The Closest Known Globul
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| Title |
M4: The Closest Known Globular Cluster |
| Explanation |
M4 is a globular cluster [ http://www.seds.org/messier/glob.html ] visible in dark skies about one degree west of the bright star Antares [ http://antwrp.gsfc.nasa.gov/apod/ap980726.html ] in the constellation [ http://www.astro.wisc.edu/~dolan/constellations/extra/constellations.html ] Scorpius [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Scorpius.html ]. M4 is perhaps the closest globular cluster [ http://antwrp.gsfc.nasa.gov/apod/globular_clusters.html ] at 7000 light years [ http://www.treasure-troves.com/astro/Light-Year.html ], meaning that we see M4 [ http://www.seds.org/messier/m/m004.html ] only as it was 7000 years ago, near the dawn of recorded human history [ http://www.hyperhistory.com/online_n2/History_n2/a.html ]. Although containing hundreds of thousands of stars and spanning over 50 light-years, M4 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1993MNRAS.265..395D ] is one of the smallest and sparsest globular clusters [ http://ast.leeds.ac.uk/research/gcs.html ] known. A particularly unusual aspect for a globular cluster is M4 [ http://www.astr.ua.edu/gifimages/m4v.html ]'s central bar of stars. M4, pictured above [ http://www.noao.edu/image_gallery/html/im0598.html ], is one of the oldest objects for which astronomers can estimate age directly. Cluster white dwarfs [ http://antwrp.gsfc.nasa.gov/apod/ap971102.html ] appear to be at least nine billion years old - so ancient they limit the youth of our entire universe [ http://www.astro.ucla.edu/~wright/cosmology_faq.html ]. |
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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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Nova Over Iran
| Title |
Nova Over Iran |
| Explanation |
A bright new nova is being studied by astronomers. The officially dubbed Nova Scorpii 2007 [ http://www.aavso.org/publications/specialnotice/33.shtml ] has become so bright in recent days that it is now visible [ http://skytonight.com/observing/home/Nova-Sco-2007.html ] to the unaided eye. Adventurous early morning sky enthusiasts [ http://antwrp.gsfc.nasa.gov/apod/ap040808.html ] should look in dark skies toward the constellation of the Scorpion [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Scorpius.html ], just below Jupiter and Antares [ http://antwrp.gsfc.nasa.gov/apod/ap980726.html ]. The above image may help as a sky chart. A nova [ http://antwrp.gsfc.nasa.gov/apod/ap060224.html ] this bright occurs only every few [ http://en.wikipedia.org/wiki/Nova#Bright_novae_since_1890 ] years. Novas [ http://csep10.phys.utk.edu/astr162/lect/novae/novae.html ] are caused by thermonuclear explosions [ http://www.youtube.com/watch?v=1KoZS-PX3VM ] casting off the outer layers of a white dwarf [ http://en.wikipedia.org/wiki/White_dwarf ] star. Pictured above on Friday, the nova was being studied through a small telescope [ http://antwrp.gsfc.nasa.gov/apod/ap050413.html ] as it appeared over the Varzaneh Desert in Isfahan [ http://en.wikipedia.org/wiki/Isfahan ], Iran [ http://en.wikipedia.org/wiki/Iran ]. The nova [ http://curious.astro.cornell.edu/question.php?number=234 ] will likely fade but remain visible with binoculars [ http://www.aavso.org/cgi-bin/newql.pl?name=V1280%20Sco&output=html ] for at least a few more days. |
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A Scorpius Sky Spectacular
| Title |
A Scorpius Sky Spectacular |
| Explanation |
If Scorpius looked this good to the unaided eye, humans might remember it better. Scorpius [ http://www.allthesky.com/constellations/scorpius/ ] more typically appears as a few bright stars in a well known but rarely pointed out zodiacal [ http://en.wikipedia.org/wiki/Zodiac ] constellation [ http://www.fillingthesky.com/constellationhistory.html ]. To get a spectacular image like this [ http://astrosurf.com/sguisard/Pagim/Scorpius_constellation-LHRVB-50mm.html ], though, one needs a good camera [ http://electronics.howstuffworks.com/digital-camera.htm ], color filters [ http://en.wikipedia.org/wiki/Filter_%28optics%29 ], and a digital image processor. To bring out detail, the above image [ http://astrosurf.com/sguisard/Pagim/Scorpius_constellation-LHRVB-50mm.html ] not only involved long duration exposures taken in several colors, but one exposure in a very specific red color [ http://antwrp.gsfc.nasa.gov/apod/ap050930.html ] emitted by hydrogen [ http://periodic.lanl.gov/elements/1.html ] that brings out great detail. The resulting image [ http://astrosurf.com/sguisard/Pagim/Scorpius_constellation-LHRVB-50mm.html ] shows many breathtaking features. Vertically across the image left is part of the plane [ http://antwrp.gsfc.nasa.gov/apod/ap050605.html ] of our Milky Way Galaxy [ http://seds.org/messier/more/mw.html ]. Visible there are vast clouds of bright stars and long filaments of dark dust [ http://antwrp.gsfc.nasa.gov/apod/ap030706.html ]. Jutting out diagonally from the Milky Way [ http://antwrp.gsfc.nasa.gov/apod/ap070123.html ] in the image center are dark dust bands known as the Dark River [ http://antwrp.gsfc.nasa.gov/apod/ap040809.html ]. This river connects to several bright stars on the right that are part of Scorpius' head and claws [ http://www.ianridpath.com/startales/scorpius.htm ], and include the bright star Antares [ http://www.astro.uiuc.edu/~kaler/sow/antares.html ]. Above and right of Antares is an even brighter planet Jupiter. Numerous red emission nebulas [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ] and blue reflection nebulas [ http://en.wikipedia.org/wiki/Reflection_nebula ] are visible throughout the image. Scorpius [ http://en.wikipedia.org/wiki/Scorpion ] appears prominently in southern skies after sunset during the middle of the year. |
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Antares
| Title |
Antares |
| Explanation |
Antares [ http://scienceweb.dao.nrc.ca/astro/skygaze060696.html ] is a huge star. In a class called red supergiant [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1992AJ%2E%2E%2E%2E104%2E%2E821M&db_key=AST&nosetcookie=1 ], Antares is about 700 times the size of our own Sun [ http://antwrp.gsfc.nasa.gov/apod/lib/sun.html ], 15 times more massive, and 10,000 times brighter. Antares [ http://www.astro.wisc.edu/~dolan/constellations/hr/6134.html ] is the brightest star in the constellation of Scorpius [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Scorpius.html ] and one of the brighter stars [ http://www.astro.wisc.edu/~dolan/constellations/extra/brightest.html ] in all the night sky. Antares [ http://www.seds.org/billa/twn/antx.html ] is surrounded by a nebula [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983ApJ%2E%2E%2E275%2E%2E704H&db_key=AST&nosetcookie=1 ] of gas which it has itself expelled. Radiation from Antares [ http://stardate.utexas.edu/radio/StarDateDB.FM$RETRIEVE?value=06/11/1996&field=ScriptAirDate&html=Test+Request+Date ]' blue stellar companion helps cause the nebular gas to glow, as photographed above. Antares [ http://www.travel-net.com/mickey/mh41.html ] is located about 500 light years away. |
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Moon Lightning
| Title |
Moon Lightning |
| Explanation |
Moonsets [ http://antwrp.gsfc.nasa.gov/apod/ap020921.html ] are not often quite as exciting as this one. But amateur astronomer Marc-Andre Besel was impressed by the brilliant lighting displays that joined the first quarter [ http://antwrp.gsfc.nasa.gov/apod/ap010428.html ] Moon and stars of the constellation Scorpius [ http://hawastsoc.org/deepsky/sco/index.html ] in western skies. On August 22, 2004, his view looked [ http://people.freenet.de/besel/ Fotoalben/Blitz/PAGE1.HTM ] across the Gulf of Mexico from Anna Maria Island, Florida, USA, a region that would experience even more stormy [ http://antwrp.gsfc.nasa.gov/apod/ap040903.html ] weather in the coming days. The alluring digital image is a time exposure, by chance [ http://images.jsc.nasa.gov/luceneweb/ fullimage.jsp?photoId=S83-40452 ] capturing the details of a brief flash of lightning [ http://thunder.msfc.nasa.gov/primer/primer2.html ] along with an overexposed Moon and dramatic cloud formations. In fact, the exposure is long enough to show the background stars as short streaks or trails [ http://www.astropix.com/HTML/ I_ASTROP/I06/I0601/I0601.HTM ]. The bright yellowish star trail, just above and right of the lightning flash, is red giant star Antares [ http://www.astro.uiuc.edu/~kaler/sow/antares.html ]. |
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