The universe is everything: all matter, energy, space, and time. Galaxies are enormous collections of stars, gas, dust, and dark matter, bound together by gravity. Space is the vast expanse containing all of this.
1. The Universe: The Big Picture
The universe is the totality of everything that exists, including all matter, energy, space, and time. It's the biggest thing we know of and contains billions of galaxies [Reference 1, Reference 3, Reference 4]. Think of it as the ultimate container.
2. Galaxies: Island Universes
A galaxy is a massive system of stars, gas, dust, and dark matter, all held together by gravity [Reference 1, Reference 2, Reference 4]. Our own galaxy, the Milky Way, contains hundreds of billions of stars, and there are billions of other galaxies in the observable universe [Reference 2, Reference 3]. Galaxies come in different shapes and sizes, including spiral, elliptical, and irregular.
- Example: The Milky Way and Andromeda galaxies are two examples of spiral galaxies.
3. Space: The Void Between
Space refers to the three-dimensional expanse that exists between celestial objects [Reference 10]. It's not empty, however; it contains various forms of matter and energy, including dark matter and dark energy, which we're still trying to fully understand. Space is the medium within which the universe exists and galaxies are located. It's the emptiness between the things.
- Distinction: The universe includes space, while space is simply the area or volume within the universe.
In short: The universe encompasses everything; galaxies are massive star systems within the universe; and space is the three-dimensional expanse that fills the universe.
