NGC 1931 (Sh2-237) in H-alpha (December 2019)

This is the h-alpha stack, 6.5 hours worth.  The area is fun because it is actually covered with h-alpha, the glow of ionized hydrogen.  Studies of NGC 1931 suggest that two clouds of gas collide here, actually generating two swarms of stars.  You can see the bow shock of one of the clouds moving towards the other.