N 164, a bright nebula, the glow of which is caused by hot stars inside it. The heating of the gas by these stars increases the pressure and causes such nebulae to expand, pushing outwards against their surroundings. A careful look at this nebula reveals locations where the expansion is encountering resistance by denser clouds of gas, producing bright, thin rims. The sky field measures 3.6 x 3.5 arcmin. North is up and East is left.
Image Credit: ESO
Explanation from: http://www.eso.org/public/images/eso0437e/