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This festive Hubble Space Telescope image resembles a holiday wreath made of sparkling lights. The bright southern hemisphere star RS Puppis is at the center of the image and is surrounded within a cocoon of reflective dust that is illuminated by the star.
RS Puppis is one of the most luminous in the class of so-called Cepheid variable stars. It rhythmically brightens and dims over a six-week cycle. The surrounding nebula flickers in brightness as pulses of light from the Cepheid propagate outwards.
Hubble took a series of photos of light flashes rippling across the nebula in a phenomenon known as a light echo. Even though light travels through space fast enough to span the gap between the Earth and the Moon in a little over a second, the nebula is so large that light can actually be photographed traversing it.
By observing the fluctuation in RS Puppis itself as well as recording the faint reflections of light pulses moving across the nebula, astronomers are able to measure these "light echoes" and determine a very accurate distance. The distance to RS Puppis has been narrowed down to 6,500 light-years.
H. Bond (STScI and Pennsylvania State University)