HII Regions and Star Forming Regions (Intro Astronomy module 8, lecture 4)
Tutorial on Stroemgren Sphere ionization
Incredibly Accurate Map of Nearby 10 Parsec Around The Solar System
In theoretical astrophysics, there can be a sphere of ionized hydrogen around a young star of the spectral classes O or B. The theory was derived by Bengt Strömgren in 1937 and later named Strömgren sphere after him. The Rosette Nebula is the most prominent example of this type of emission nebula from the H II-regions.