Explanation:
This dusty reflection nebula surrounds pulsating
star RS Pup, some 10 times more massive than the 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.
The otherwise overwhelming light from RS Pup itself is
hidden behind the dark central stripe in the color image.
Using
new 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.
digg_url = 'http://apod.nasa.gov/apod/ap080212.html'; digg_skin = 'compact';
