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Glossary term: Gas

Description: In physics, gas is a state of matter where the molecules or atoms are not in any way bound to each other, but instead are in constant, chaotic motion, atoms and molecules going every which way at different speeds. The air we breath is a mixture of gasses such as nitrogen and oxygen. The mean energy of motion is a measure for the temperature of the gas, and the main effect responsible for a gas's pressure (exerted, for instance, upon the walls of a container) is gas particles hitting those walls and recoiling. In astronomy, one may encounter interstellar gas clouds, giant molecular clouds, intergalactic gas or the gas of planetary atmosphere. In a slight misuse of language, astronomers also refer to plasma (where the atoms in question are ionized) as gas – for example when they call stars "balls of gas" or refer to gas swirling in an accretion disk.

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Term and definition status: This term and its definition is still awaiting approval

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".