Subj : Daily APOD Report To : All From : Ben Ritchey Date : Wed May 15 2019 07:33:04 Astronomy Picture of the Day Astronomy Picture of the Day Discover the cosmos! [1] Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2019 May 15 [2] Anemic Spiral NGC 4921 from Hubble Image Credit: NASA [3] , ESA [4] , Hubble [5] ; Processing & Copyright: Kem Cook [6] (LLNL [7] ) & Leo Shatz [8] Explanation: How far away is spiral galaxy NGC 4921? It's surpringly important to know. Although presently estimated to be about 300 million light years [9] distant, a more precise determination could be coupled with its known recession speed [10] to help humanity better calibrate the expansion rate [11] of the entire visible universe [12] . Toward this goal [13] , several images were taken [14] by the Hubble Space Telescope [15] in order to help identify key stellar distance markers known as Cepheid [16] variable [17] stars. Since NGC 4921 [18] is a member of the Coma Cluster of Galaxies [19] , refining its distance [20] would also allow a better distance determination [21] to one of the largest nearby clusters in the local universe. The magnificent spiral NGC 4921 [22] has been informally dubbed anemic [23] because of its low rate of star [24] formation and low surface brightness [25] . Visible [26] in the featured image [27] are, from the center, a bright nucleus, a bright central bar [28] , a prominent ring [29] of dark dust [30] , blue clusters [31] of recently formed stars, several smaller companion galaxies [32] , unrelated galaxies in the far distant universe [33] , and unrelated stars in our Milky Way Galaxy [34] . 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[76] ---------- Site notes: [1] arcfhivepix.html [2] image/1905/NGC4921_HubbleShatz_4046.jpg [3] https://www.nasa.gov/ [4] https://www.esa.int/ESA [5] https://hla.stsci.edu/ [6] http://heritage.stsci.edu/2010/24/bio/bio_primary.html [7] https://st.llnl.gov/ [8] http://www.astrobin.com/users/spinlock/ [9] http://chandra.harvard.edu/photo/cosmic_distance.html [10] http://en.wikipedia.org/wiki/Metric_expansion_of_space [11] http://apod.nasa.gov/debate/debate96.html [12] ap180508.html [13] http://archive.stsci.edu/proposal_search.php?mission=hst&id=12476 [14] http://hla.stsci.edu/ hlaview. html#Inventory|filterText%3D%24filterTypes%3D|query_ string=NGC%204921&posfilename=&poslocalname=&posfilecount=&listdelimiter=whites pace&listformat=degrees&RA=195.358960&Dec=27.885940&Radius=0. 020833&inst- control=all&inst=ACS&inst=ACSGrism&inst=WFC3&inst=WFPC2&inst=NICMOS&inst=NICGRI SM&inst=COS&inst=WFPC2- PC&inst=STIS&inst=FOS&inst=GHRS&imagetype=best&prop_id=&spectral_ elt=&proprietary=both&preview=1&output_size=256&cutout_size=12. 8|ra=&dec=&sr=&level=&image=&inst=ACS%2CACSGrism%2CWFC3%2CWFPC2%2CNICMOS%2CNICG RISM%2CCOS%2CWFPC2-PC%2CSTIS%2CFOS%2CGHRS&ds= [15] http://en.wikipedia.org/wiki/Hubble_Space_Telescope [16] http://en.wikipedia.org/wiki/Cepheid_variable [17] http://www.phys.ufl.edu/~buchler/ceph/anim.html [18] http://en.wikipedia.org/wiki/NGC_4921 [19] ap180326.html [20] http://adsabs.harvard.edu/abs/2016ApJ...819...77L [21] http://abyss.uoregon.edu/~js/ast123/lectures/lec13.html [22] http://www.youtube.com/watch?v=6uAjKlkiQ_I [23] http://en.wikipedia.org/wiki/Anemic [24] https://spaceplace.nasa.gov/search/stars/ [25] http://nedwww.ipac.caltech.edu/level5/March01/Impey/frames.html [26] http://www.spacetelescope.org/news/html/heic0901.html [27] http://www.astrobin.com/403935/ [28] ap050825.html [29] ap991212.html [30] http://en.wikipedia.org/wiki/Cosmic_dust [31] ap081209.html [32] ap080909.html [33] ap180305.html [34] http://cass.ucsd.edu/public/tutorial/MW.html [35] http://www.apodar.com/ [36] http://www.apod.cat/ [37] http://www.bjp.org.cn/apod/today.html [38] http://sprite.phys.ncku.edu.tw/astrolab/mirrors/apod/apod.html [39] http://www.apod.rs/Croatia.html [40] http://www.astro.cz/apod/ [41] http://www.apod.nl/ [42] http://www.starobserver.org/ [43] http://www.cidehom.com/apod.php [44] https://www.apod.tv/ [45] http://www.astronomia2009.org.il/info/apod/apod.htm [46] http://apod.infoastronomy.org/ [47] http://home.u05.itscom.net/apodjpn/apodj/apodj0.htm [48] http://wouldyoulike.org/apod/ [49] http://www.apod.rs/Montenegro.html [50] http://apod.pl/apod/ [51] http://www.astronet.ru/db/apod.html [52] http://www.apod.rs/ [53] http://apod.fmf.uni-lj.si/ [54] http://observatorio.info/ [55] http://astronomy.pp.ua/ [56] ap190514.html [57] archivepix.html [58] lib/apsubmit2015.html [59] lib/aptree.html [60] https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search [61] calendar/allyears.html [62] /apod.rss [63] lib/edlinks.html [64] lib/about_apod.html [65] http://asterisk.apod.com/discuss_apod.php?date=190515 [66] ap190516.html [67] http://www.phy.mtu.edu/faculty/Nemiroff.html [68] http://www.phy.mtu.edu/ [69] https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html [70] http://www.astro.umd.edu/ [71] lib/about_apod.html#srapply [72] https://www.nasa.gov/about/highlights/HP_Privacy.html [73] https://astrophysics.gsfc.nasa.gov/ [74] https://www.nasa.gov/ [75] https://www.nasa.gov/centers/goddard/ [76] http://www.mtu.edu/ --- Mystic BBS v1.12 A43 (Windows/32) * Origin: FIDONet - The Positronium Repository (1:393/68) .