It is one of the most important stars in the sky. This is partly because, by
coincidence, it is surrounded by a dazzling reflection nebula.
Pulsating RS Puppis, 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 variable star, a class of stars
whose brightness
is used to estimate distances to nearby galaxies as one of the first steps in
establishing the cosmic distance
scale. As RS Pup pulsates
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. Using
measurements of the time delay and angular size of the nebula, the known speed of
light allows astronomers to geometrically determine the distance to RS Pup to be 6,500 light-years, with
a remarkably small error of plus or minus 90 light-years. An impressive
achievement for stellar astronomy, the echo-measured distance also more
accurately establishes the true brightness of RS
Pup, and by extension other Cepheid stars, improving the knowledge of distances
to galaxies beyond the
Milky Way.
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