These pictures show a star before and after it has had a radical
makeover. The 'before' picture on the left is an artist's
drawing of where the different ingredients inside a massive star
used to be found. These ingredients are called chemical
elements. On the right, the 'after' picture is a real space
photo of the same star after a massive explosion blew away the
star's outer parts. Astronomers call an explosion like this a
supernova and all of the star material after the explosion is
called a supernova remnant. The supernova remnant shown here (in
the photo on the right) is called Cassiopeia A, or just Cas A
for short. In both pictures the same colors have been used to
show the different chemical elements in the star. Before the
explosion, astronomers think that the star had lots of the
chemical element iron (shown in blue) and sulphur and silicon
(shown in green) at its center. But afterwards, these chemical
elements were flung towards the outer edges of the star, as
shown by the blue and green colors arou