Subj : Daily APOD Report To : All From : Ben Ritchey Date : Fri May 17 2019 07:19:01 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 17 [2] RS Puppis Image Credit & Copyright [3] : Image Data: NASA [4] , ESA [5] , Hubble Legacy Archive [6] ; Processing & Copyright: Rogelio Bernal Andreo [7] (DeepSkyColors.com [8] ) Explanation: Pulsating RS Puppis [9] , the brightest star in the image center [10] , is some ten times more massive than our Sun and on average 15,000 times more luminous. In fact, RS Pup is a Cepheid variable star [11] , a class of stars whose brightness [12] is used to estimate distances to nearby galaxies as one of the first steps in establishing the cosmic distance [13] scale. As RS Pup pulsates [14] over a period of about 40 days, its regular changes in brightness are also seen along its surrounding nebula [15] delayed in time, effectively a light echo [16] . Using measurements of the time delay and angular size of the nebula, the known speed of light [17] allows astronomers to geometrically determine the distance to RS Pup [18] to be 6,500 light-years, with a remarkably small error of plus or minus 90 light-years [19] . An impressive achievement for stellar astronomy, the echo-measured [20] distance also more accurately establishes the true brightness of RS Pup [21] , and by extension other Cepheid stars, improving the knowledge of distances to galaxies beyond the Milky Way. Tomorrow's picture: pixels in space ------------------------------------------------------------------------------- < [22] | Archive [23] | Submissions [24] | Index [25] | Search [26] | Calendar [27] | RSS [28] | Education [29] | About APOD [30] | Discuss [31] | > [32] ------------------------------------------------------------------------------- Authors & editors: Robert Nemiroff [33] (MTU [34] ) & Jerry Bonnell [35] (UMCP [36] ) NASA Official: Phillip Newman Specific rights apply [37] . NASA Web Privacy Policy and Important Notices [38] A service of: ASD [39] at NASA [40] / GSFC [41] & Michigan Tech. U. [42] ---------- Site notes: [1] archivepix.html [2] image/1905/RSPuppis_Hubble_rba.jpg [3] lib/about_apod.html#srapply [4] https://www.nasa.gov/ [5] https://www.esa.int/About_Us/Welcome_to_ESA [6] https://hla.stsci.edu/ [7] https://en.wikipedia.org/wiki/Rogelio_Bernal_Andreo [8] http://www.deepskycolors.com/ [9] http://en.wikipedia.org/wiki/RS_Pup [10] https://www.facebook.com/DeepSkyColors/photos/ a.511542708913047/2161804837220151/?type=3&theater [11] http://www.aavso.org/types-variables [12] http://hyperphysics.phy-astr.gsu.edu/hbase/astro/ cepheid.html#c2 [13] http://en.wikipedia.org/wiki/Cosmic_distance_ladder [14] http://www.eso.org/public/news/eso0805/ [15] http://hubblesite.org/video/748 [16] http://en.wikipedia.org/wiki/Light_echo [17] http://www.physics.umd.edu/icpe/newsletters/n34/ marshmal.htm [18] http://www.aavso.org/vsots_rspup [19] https://starchild.gsfc.nasa.gov/docs/StarChild/questions/ question19.html [20] https://arxiv.org/abs/0802.1501 [21] http://www.eso.org/sci/publications/messenger/archive/ no.150-dec12/messenger-no150-46-48.pdf [22] ap190516.html [23] archivepix.html [24] lib/apsubmit2015.html [25] lib/aptree.html [26] https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search [27] calendar/allyears.html [28] /apod.rss [29] lib/edlinks.html [30] lib/about_apod.html [31] http://asterisk.apod.com/discuss_apod.php?date=190517 [32] ap190518.html [33] http://www.phy.mtu.edu/faculty/Nemiroff.html [34] http://www.phy.mtu.edu/ [35] https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html [36] http://www.astro.umd.edu/ [37] lib/about_apod.html#srapply [38] https://www.nasa.gov/about/highlights/HP_Privacy.html [39] https://astrophysics.gsfc.nasa.gov/ [40] https://www.nasa.gov/ [41] https://www.nasa.gov/centers/goddard/ [42] http://www.mtu.edu/ --- Mystic BBS v1.12 A43 (Windows/32) * Origin: FIDONet - The Positronium Repository (1:393/68) .