Exploring Nature Series. The Interstellar Chapter

Author: Editorial Committee of the Series
Publisher:
Publish Date: 2004-01-01
Features: Explore Nature Series. The universe refers to the vast space and the various celestial bodies and diffuse matter within it. There are concepts of the "observed universe" and the "physical universe." The "observed universe" is the entire cosmic space and the various celestial bodies and diffuse matter that can be observed by the naked eye or instruments. It has a boundary, which is the limit of contemporary detection tools. Currently, it is possible to observe stars up to 20 billion light-years away. This range contains over 1 billion galaxies.