Galactic spiral structure.
Bok
B J
BJ
D055580:Astronomical Phenomena; D001256:Astronomy; D005118:Extraterrestrial Environment / Q000737:chemistry*; D005740:Gases; D006859:Hydrogen / Q000032:analysis* / Q000737:chemistry; D008962:Models, Theoretical
D005740:Gases; D006859:Hydrogen