Glossary term: Hydrogen

Description: Hydrogen is the most abundant and lightest element in the Universe; it has the smallest nuclear charge (one proton). When hydrogen atoms are excited, for instance by a nearby hot star, they emit light in characteristic narrow regions of the spectrum. These hydrogen emission lines can be used to detect atomic hydrogen; in particular the hydrogen alpha line, with its rich red color, makes hydrogen clouds show up in splendid red in astronomical images.

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The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".