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

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    Authors & editors: Robert Nemiroff [33] (MTU [34] ) & Jerry Bonnell [35]
                                  (UMCP [36] )
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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_...
  [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/as... cepheid.html#c2
  [13] http://en.wikipedia.org/wiki/Cosmic_distance_...
  [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/n... marshmal.htm
  [18] http://www.aavso.org/vsots_rspup
  [19] https://starchild.gsfc.nasa.gov/docs/StarChil...
question19.html
  [20] https://arxiv.org/abs/0802.1501
  [21] http://www.eso.org/sci/publications/messenger...
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/apo...
  [27] calendar/allyears.html
  [28] /apod.rss
  [29] lib/edlinks.html
  [30] lib/about_apod.html
  [31] http://asterisk.apod.com/discuss_apod.php?dat...
  [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/jbonnel...
  [36] http://www.astro.umd.edu/
  [37] lib/about_apod.html#srapply
  [38] https://www.nasa.gov/about/highlights/HP_Priv...
  [39] https://astrophysics.gsfc.nasa.gov/
  [40] https://www.nasa.gov/
  [41] https://www.nasa.gov/centers/goddard/
  [42] http://www.mtu.edu/

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