Complex sentence: The Veil Nebula is one component of the large but relatively faint spherical residue of a supernova; the source star exploded some 5,000 to 8,000 years ago.
Split into simpler sentences: The Veil Nebula is one component of the residue of a large but relatively faint supernova remnant. The source supernova exploded some 5,000 to 8,000 years ago.