Bull's, err, Cat's Eye - May 4, 2002
This detailed Hubble image of the Cat's Eye Nebula, discovered in 1786, reveals a bull's eye pattern of at least eleven concentric rings around the nebula’s glowing nucleus, a dying Sun-like star. Each 'ring' represents a spherical layer of gas and dust ejected by the star, an event that occurs in 1,500-year intervals. Why this happens is unknown. Some astronomers think that the pulses may occur in sync with the star’s magnetic activity or with the gravitational pull of stars orbiting nearby.