Distance: 7500 Light Years
by Robert Gendler
The glowing emission clouds are thin blisters formed at the surface of several giant molecular clouds.
The clouds of initially cold neutral gas have fragmented and condensed in many areas, forming clusters of bright young stars collectively known as the Cas OB6 association. The bright O and B type giants of Cas OB6 illuminate the chain of giant HII clouds.
Star formation within these HII regions has occurred sequentially over time as young OB stars have triggered bursts of new star formation as the HII clouds they illuminate expand into and compress the surrounding denser gaseous medium. The oldest clusters formed first in IC 1805 some 4 million years ago.