Westerhout 5

Westerhout 5 is an emission nebula located in Cassiopeia. Several small open clusters are embedded in the nebula: Collinder 33 and 34 in the head and IC 1848 in the body.
The small emission nebula IC 1871 is present just left of the top of the head, and Sh2 199 is just below the lower back area.
The object is often called by the cluster designation IC 1848. W5 with W3 and W4 forms part of the larger W3/W4/W5 Complex.
The galaxies Maffei 1 and Maffei 2 are both located in apparent proximity to the nebula, although light extinction from the Milky Way makes them very hard to see.
Once thought to be part of the Local Group, they are now known to belong to their own group – the IC 342/Maffei Group.
Westerhout 5 is the eastern neighbor of IC 1805 and the two are often mentioned together as the "Heart and Soul".

Star formation

W5, a radio source within the nebula, spans an area of sky equivalent to four full moons and is about 6,500 light-years away in the constellation Cassiopeia. Like other massive star-forming regions, such as Orion and Carina, W5 contains large cavities that were carved out by radiation and winds from the region's most massive stars. According to the theory of triggered star formation, the carving out of these cavities pushes gas together, causing it to ignite into successive generations of new stars. The image in the gallery above contains some of the best evidence yet for the triggered star formation theory. Scientists analyzing the photo have been able to show that the ages of the stars become progressively and systematically younger with distance from the center of the cavities.