1. The totality of space, matter, and radiation that is potentially comprehensible.
2. The whole cosmic system of matter and energy of which earth, and therefore the human race, is a part.

Humanity has traveled a long road since societies imagined earth, the sun, and the moon as the main objects of creation, with the rest of the universe being formed almost as an afterthought.

Today it is known that the earth is only a small ball of rock in a space of unimaginable vastness and that the birth of the solar system was probably only one event among many that occurred against the backdrop of an already mature universe.

3. All of the space and its contents, the study of which is called cosmology.

The universe has been determined to be mostly empty space, dotted with stars collected into vast aggregations called galaxies for as far as telescopes can see.

The most distant detected galaxies and quasars (quasi-stellar objects) lie ten billion light-years or more from the earth, and are moving farther apart as the universe expands.

A feature of our universe deduced from the observation that the distant galaxies' light is red-shifted.

Observations so far have not succeeded in determining whether the universe is open (of infinite extent in space) or closed (of finite extent) and whether the universe in the future will continue to expand indefinitely or will eventually collapse back into an extremely dense, congested state.