An HII region in the northern parts of Perseus, NGC 1491 represents a part of a cloud of gas that is illuminated from within by the light of the hot O-typestar BD +50 886. In the heart of the nebula, the illuminated gas forms branching tendrils around the star, while the star's own stellar wind has carved out an expanding spherical bubble around it.
The illuminating star of the nebula, BD +50 886, can be seen slightly to the east (left) of centre in this image, within the spherical 'bubble' created by its stellar wind, eroding the gases of the nebula from within. Imagery provided by Aladin sky atlas
The gases of the nebula trail away to the eastward of its brighter regions, gradually fading from view as recede from the illuminating star, and dark patches obscure some regions of the surrounding cloud. Estimates of the distance to the nebula vary around a value of some ten thousand light years, and based on that distance the visible nebula would measure some fourteen light years across, although this brighter region represents only a small portion of the entire unilluminated cloud.