Skip to ContentGo to accessibility pageKeyboard shortcuts menu
OpenStax Logo
Astronomy

Key Terms

AstronomyKey Terms

central bulge
(or nuclear bulge) the central (round) part of the Milky Way or a similar galaxy
dark matter
nonluminous mass, whose presence can be inferred only because of its gravitational influence on luminous matter; the composition of the dark matter is not known
dark matter halo
the mass in the Milky Way that extends well beyond the boundary of the luminous stars to a distance of at least 200,000 light-years from the center of the Galaxy; although we deduce its existence from its gravity, the composition of this matter remains a mystery
differential galactic rotation
the idea that different parts of the Galaxy turn at different rates, since the parts of the Galaxy follow Kepler’s third law: more distant objects take longer to complete one full orbit around the center of the Galaxy
halo
the outermost extent of our Galaxy (or another galaxy), containing a sparse distribution of stars and globular clusters in a more or less spherical distribution
Milky Way Galaxy
the band of light encircling the sky, which is due to the many stars and diffuse nebulae lying near the plane of the Milky Way Galaxy
population I star
a star containing heavy elements; typically young and found in the disk
population II star
a star with very low abundance of heavy elements; found throughout the Galaxy
spiral arm
a spiral-shaped region, characterized by relatively dense interstellar material and young stars, that is observed in the disks of spiral galaxies
supermassive black hole
the object in the center of most large galaxies that is so massive and compact that light cannot escape from it; the Milky Way’s supermassive black hole contains 4.6 millions of Suns’ worth of mass
Order a print copy

As an Amazon Associate we earn from qualifying purchases.

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.