Subj : Daily APOD Report To : All From : Ben Ritchey Date : Wed Aug 29 2018 06:34:00 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. 2018 August 29 [2] Nearby Cepheid Variable RS Pup Image Credit: NASA [3] , ESA [4] , Hubble Heritage [5] Team; Acknowledgement: Howard Bond [6] (STScI [7] & Penn State U. [8] ) Explanation: In the center is one of the most important stars on the sky. This is partly because, by coincidence, it is surrounded by a dazzling reflection nebula [9] . Pulsating RS Puppis [10] , the brightest star in the image center, is some ten times more massive than our Sun and on average 15,000 times more luminous. In fact, RS Pup is a Cepheid type [11] variable star [12] , a class of stars whose brightness [13] is used to estimate distances to nearby galaxies as one of the first steps in establishing the cosmic distance [14] scale. As RS Pup pulsates [15] over a period of about 40 days, its regular changes in brightness are also seen along the nebula 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 [22] to galaxies beyond [23] the Milky Way. The featured image [24] was taken by the Hubble Space Telescope [25] . Tomorrow's picture: open space ------------------------------------------------------------------------------- < [26] | Archive [27] | Submissions [28] | Index [29] | Search [30] | Calendar [31] | RSS [32] | Education [33] | About APOD [34] | Discuss [35] | > [36] ------------------------------------------------------------------------------- Authors & editors: Robert Nemiroff [37] (MTU [38] ) & Jerry Bonnell [39] (UMCP [40] ) NASA Official: Phillip Newman Specific rights apply [41] . NASA Web Privacy Policy and Important Notices [42] A service of: ASD [43] at NASA [44] / GSFC [45] & Michigan Tech. U. [46] ---------- Site notes: [1] archivepix.html [2] image/1808/RSPup_HubbleBond_3981.jpg [3] http://www.nasa.gov/ [4] http://www.spacetelescope.org/ [5] http://heritage.stsci.edu/ [6] http://www.stsci.edu/~bond/ [7] http://www.stsci.edu/ [8] http://astro.psu.edu/ [9] http://apod.nasa.gov/apod/reflection_nebulae.html [10] http://en.wikipedia.org/wiki/RS_Pup [11] ap960110.html [12] http://www.aavso.org/types-variables [13] http://hyperphysics.phy-astr.gsu.edu/hbase/astro/ cepheid.html#c2 [14] http://en.wikipedia.org/wiki/Cosmic_distance_ladder [15] http://www.eso.org/public/news/eso0805/ [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] http://www.astro.ucla.edu/~wright/distance.htm [23] http://www.atlasoftheuniverse.com/virgo.html [24] http://www.spacetelescope.org/images/heic1323a/ [25] http://hubblesite.org/the_telescope/ [26] ap180828.html [27] archivepix.html [28] lib/apsubmit2015.html [29] lib/aptree.html [30] https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search [31] calendar/allyears.html [32] /apod.rss [33] lib/edlinks.html [34] lib/about_apod.html [35] http://asterisk.apod.com/discuss_apod.php?date=180829 [36] ap180830.html [37] http://www.phy.mtu.edu/faculty/Nemiroff.html [38] http://www.phy.mtu.edu/ [39] https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html [40] http://www.astro.umd.edu/ [41] lib/about_apod.html#srapply [42] https://www.nasa.gov/about/highlights/HP_Privacy.html [43] https://astrophysics.gsfc.nasa.gov/ [44] https://www.nasa.gov/ [45] https://www.nasa.gov/centers/goddard/ [46] http://www.mtu.edu/ --- Mystic BBS v1.12 A39 (Windows/32) * Origin: FIDONet - The Positronium Repository (1:393/68) .