Skip to ContentGo to accessibility pageKeyboard shortcuts menu
OpenStax Logo
Astronomy

Key Terms

AstronomyKey Terms

baryon cycle
the cycling of mass in and out of the interstellar medium, including accretion of gas from intergalactic space, loss of gas back into intergalactic space, and conversion of interstellar gas into stars
cosmic rays
atomic nuclei (mostly protons) and electrons that are observed to strike Earth’s atmosphere with exceedingly high energies.
H II region
the region of ionized hydrogen in interstellar space
interstellar dust
tiny solid grains in interstellar space thought to consist of a core of rocklike material (silicates) or graphite surrounded by a mantle of ices; water, methane, and ammonia are probably the most abundant ices
interstellar extinction
the attenuation or absorption of light by dust in the interstellar medium
interstellar medium (ISM)
(or interstellar matter) the gas and dust between the stars in a galaxy
Local Bubble
(or Local Hot Bubble) a region of low-density, million degree gas in which the Sun and solar system are currently located
Local Fluff
a slightly denser cloud inside the Local Bubble, inside which the Sun also lies
molecular cloud
a large, dense, cold interstellar cloud; because of its size and density, this type of cloud can keep ultraviolet radiation from reaching its interior, where molecules are able to form
nebula
a cloud of interstellar gas or dust; the term is most often used for clouds that are seen to glow with visible light or infrared
reddening (interstellar)
the reddening of starlight passing through interstellar dust because dust scatters blue light more effectively than red
Citation/Attribution

This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's permission.

Want to cite, share, or modify this book? This book uses the Creative Commons Attribution License and you must attribute OpenStax.

Attribution information
  • If you are redistributing all or part of this book in a print format, then you must include on every physical page the following attribution:
    Access for free at https://openstax.org/books/astronomy/pages/1-introduction
  • If you are redistributing all or part of this book in a digital format, then you must include on every digital page view the following attribution:
    Access for free at https://openstax.org/books/astronomy/pages/1-introduction
Citation information

© Jan 28, 2022 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License . The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.