By the term universe, astronomers mean

By the term universe, astronomers mean

A the collection of several dozen galaxies, of which the Milky Way is one.

B the realm inside the atom.

C everything that we can observe.

D the system of the Sun, its planets and moons, and small pieces of debris that surround it.

E the system of 200 to 400 billion stars, of which the Sun is one.

The correct answer and explanation is :

The correct answer is C: everything that we can observe.

This definition refers to the term “the universe.” The universe is the totality of all space, time, matter, energy, and the physical laws that govern them. It includes all galaxies, stars, planets, nebulae, black holes, and every other form of matter and energy that exists, whether we are currently able to observe it or not.

Explanation:

1. A: The collection of several dozen galaxies, of which the Milky Way is one.

• This refers to a galaxy cluster or supercluster, which is a large grouping of galaxies. The Milky Way is part of the Local Group of galaxies, and our galaxy itself is just one among many billions in the universe. While galaxies are a key component of the universe, the universe is far larger than just a few dozen galaxies.

1. B: The realm inside the atom.

• This refers to atomic structure, particularly the realm of subatomic particles like electrons, protons, and neutrons. It is on a microscopic scale and is not synonymous with the universe, which spans all scales, from the tiniest particles to the largest cosmic structures.

1. D: The system of the Sun, its planets and moons, and small pieces of debris that surround it.

• This refers to the solar system, a specific region of space within the universe. While the solar system is an essential component of the universe, it is only a small fraction of the larger cosmic structure. The universe contains countless solar systems, galaxies, and other celestial objects.

1. E: The system of 200 to 400 billion stars, of which the Sun is one.

• This refers to a galaxy, specifically the Milky Way, which contains hundreds of billions of stars. A galaxy is part of the universe but is still just one of billions within it.

The universe encompasses everything observable, including galaxies, stars, planets, and all matter and energy. It is the vast, all-encompassing reality that contains everything we can observe, from the smallest particles to the largest cosmic structures.