NASA says the Hubble Space Telescope has been observing a "super" star in the southern hemisphere whose rhythmic brightening provides a holiday light show. The star RS Puppis is swaddled in a gossamer cocoon of reflective dust, illuminated by the glittering star that brightens and dims over a six-week cycle, the Space Telescope Science Institute reported Tuesday. Ten times as massive as the sun, and 200 times larger, RS Puppis is one of the most luminous in the class of so-called Cepheid variable stars, with an average brightness 15,000 times greater than the sun's, astronomers said. The surrounding nebula flickers in brightness as pulses of light from the star propagate outward, crossing distances so large that reflected light can be photographed traversing the nebula, they said. The fluctuations of light within the nebular have allowed astronomers to pin down a very accurate distance for RS Puppis, now determined to be 6,500 light years from Earth.