RS Puppis (or RS Pup) is a Cepheid variable star around 6,000 light years away in the constellation of Puppis. It is one of the biggest and brightest known Cepheids in the Milky Way galaxy and has one of the longest periods for this class of star at 41.5 days.
RS Puppis is a supergiant with a spectral classification of G2Ib, although its spectral type varies between F9 and G7 as its temperature changes. It lies on the instability strip and based on the rate of change of its period is thought to be crossing it for the third time. The third crossing occurs as a star is evolving towards cooler temperatures for the second time after performing a blue loop. The third crossing of the instability strip occurs much more slowly than the first crossing just after a star leaves the main sequence.
The distance to RS Puppis is important because Cepheids serve as a marker for distances within the Milky Way galaxy and for nearby galaxies.
Credits: Wikipedia, NASA, ESA, Hubble
Heritage Team; Acknowledgement: Howard Bond (STScl & Penn State U.)
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