Description:
Sh2-187 is a compact emission nebula (H II region) located in the constellation Cassiopeia, close to the rich star-forming regions of the Perseus arm. It is composed of ionized hydrogen gas excited by young, massive stars embedded within or just behind the nebula. As a result, Sh2-187 glows strongly in H-alpha, giving it a soft red appearance in narrowband images.
Unlike large, dramatic nebulae, Sh2-187 is relatively small and faint. It lies within a complex interstellar environment that includes molecular clouds and dust, indicating ongoing or recent star formation. Traces of O III emission can sometimes be detected, but hydrogen emission dominates its structure.