The Astronautics Vocabulary is a glossary of terms that pertain to the science and technology of spaceflight. This alphabetical list can be navigated by clicking on the letters A-Z displayed on this page.
Definition: An invisible form of matter whose nature is unknown. It is thought to exert a gravitational influence like ordinary matter, and to explain the permanence of large structures like galaxies or galaxy clusters in the universe. There is no unanimity within the scientific community about the existence of dark matter. (See dark energy and ordinary matter.)