The Hubble telescope has given astronomers their best look yet at a rapidly ballooning bubble of gas blasted off a star.

The shell surrounds Nova Cygni 1992, which erupted Feb. 19, 1992. A nova is a thermonuclear explosion that occurs on the surface of a white dwarf star in a double-star system. The image [right], taken after Hubble's near-sightedness had been corrected, reveals an elliptical and slightly lumpy ring-like structure. The ring is the edge of a bubble of hot gas blasted into space by the nova. Another Hubble picture taken 467 days after the explosion [left] provided the first glimpse of the ring and a mysterious bar-like structure. But the image interpretation was severely hampered by the telescope's blurred vision.