Between the Stars: Gas and Dust in Space (Astronomy)

Recall cards on the interstellar medium, the gas and dust between the stars. The mix: about 99% gas and 1% dust, mostly hydrogen and helium, totaling roughly 15% of the Galaxy's stellar mass. Interstellar gas: hot ionized H II regions and their red H-alpha glow, cool neutral hydrogen and the 21-centimeter line, ultra-hot supernova gas, and cold giant molecular clouds rich in molecules. Cosmic dust: tiny grains with rocky cores and icy mantles that cause extinction, reddening, and reflection and dark nebulae. Cosmic rays: high-speed nuclei and electrons, mostly protons, arriving near light speed. The life cycle of cosmic material as stars return enriched gas and dust to space. And the Sun's own neighborhood, the hot Local Bubble and the Local Fluff cloud around us.