HI shells
type: Concept
broader: H I regions

Nebulae
type: Concept
narrower: H I regions

H I regions
type: Concept
modified: 2020-11-02T15:57:58.504Z
modified: 2020-11-02T15:58:10.217Z
broader: Nebulae
narrower: HI shells
definition: A region of neutral (atomic) hydrogen in interstellar space. At least 95 percent of interstellar hydrogen is H I. It emits radio waves that are 21 cm long.
alternative label: HI regions
contributor: AAS Frey.Katie Admin
related: Astrochemistry

Astrochemistry
type: Concept
related: H I regions