Cometary Knots in the Helix Nebula . ... Credit Copyright: R. O'Dell and K. Handron (Rice University ), NASA Explanation: Four hundred fifty light-years from Earth, the wind from a dying, sun-like star produced a planetary nebula popularly known as the Helix . ... Previously known from ground based observations, the sheer number of cometary knots found in this single nebula is astonishing . ... NASA Web Site Statements, Warnings, and Disclaimers . ... U. Based on Astronomy Picture Of the Day ...