hydrogen clouds A Map of the Milky Way http://www.atlasoftheuniverse.com/milkyway.html hydrogen clouds hydrogen clouds http://www.atlasoftheuniverse.com/milkyway.html hydrogen clouds http://www.atlasoftheuniverse.com/milkyway.html A Map of the Milky Way a couple of thousand light-years thick hydrogen clouds hydrogen clouds spiral arms http://www.atlasoftheuniverse.com/milkyway.html hydrogen clouds Milky Way Galaxy http://www.atlasoftheuniverse.com/milkyway.html http://www.atlasoftheuniverse.com/milkyway.html Kaart van de Melkweg hydrogen clouds hydrogen clouds 3000 light-years wide hydrogen clouds http://www.atlasoftheuniverse.com/milkyway.html Milky Way Galaxy