The Differences Between a Solar System, Universe and Galaxy

The Differences Between a Solar System, Universe and Galaxy

Space is a fascinating thing, one that’s captured humanity’s imagination for hundreds of thousands of years. You look to the night sky and view a sea of stars, no doubt filled with questions. How’d it all get here? There are other fascinating questions too, regarding galaxies and the universe. For instance, what are the differences between a solar system vs. a galaxy?

While breaking down everything there is to know about a galaxy (not to mention the universe) would take a long time, we’re happy to go over some fascinating basics in hopes to assist your curious mind. And if this article doesn’t satisfy your curiosity, we’ve got some great solar system books for kids right here!

Defining the Terms

Before we establish the key differences between a solar system, galaxy, and our universe, let’s briefly define them!

Solar System

Typically this refers to our own solar system – a collection of eight planets and stellar objects orbiting the Sun. It can also refer to systems of planets orbiting a star, such as the kinds astronomers observe today. (Looking for a great solar system mobile? Click here!)


Galaxies are systems composed of billions upon billions of stars. They are also clusters of stellar objects like planets, asteroids, comets, and other different objects.


The collection of all known living and stellar objects. Contains all galaxies, stars, and planets. It is unknown of the universe has a limit.

That sounds pretty big, doesn’t it? Well, it is. The amount of stars in the known universe are more than the grains of sand here on Earth. It’s difficult to comprehend all that in one go!

Between a Galaxy and a Solar System

Between a Galaxy and a Solar System

So you have a basic idea about how a solar system and galaxy are different: most notably in size. Since a solar system contains one star and a galaxy contains billions of them, it’s easy to see that the latter is far bigger in stellar scope. Not to mention, there are thousands of galaxies in the observable universe (and that’s a low number).

Some of the smaller differences come down to distance. In a solar system, planets are held together by a sun’s gravity, which is also true for a galaxy. A galaxy holds itself together by gravity as well, though the distance between different suns, stars, and planets are immense. (If you’re looking to get a close up view of our local star, check out these solar telescopes!)

For instance, we cannot realistically travel to another star system. The closest star to our own is Proxima Centauri, about 4.5 light years away (a light year is the total distance light travels in one year). That’s a lot of distance! For a comparison, it might take a spacecraft 30 years to reach Mars given our current technology. (Looking for some info about eclipses? Check out the differences between solar and lunar eclipses here!)

What about the universe?

Comparing our solar system to the universe is like an ant with a mountain. It’s vast, filled with everything we’ve ever known or will ever know. Astronomers have been making observations about the universe since the invention of the telescope, slowly piecing together bits and fragments of the cosmos.

A big universe has big questions, and even bigger answers. While scientists and astronomers still strive to learn everything about it, we still don’t know it all. However, through examinations, probe imagery, and scientific methods, scientists have put together a basic profile about our known universe.

We’ve discussed at length how the solar system, but we’ll take a moment to describe the universe’s origin (or the current accepted theory). This, in part, will also explain how large it is, and how we determine.

It starts with the Big Bang Theory. While we’d love to know what occurred before the bang, our current understanding is superhot material collided together producing a gigantic cosmic explosion which seeded the empty universe with all the material needed for creating stars, planets, and life.

The process by which stars and planets formed is also complicated, but all that stellar material – over the course of billions of years – allowed for the birth of suns and eventually galaxies, then solar systems. As far as how “big” the universe is, astronomers observe an expansion of about 46 billion light years. Essentially, using super powerful telescopes, they peer back into space to see ancient stars.

However, it’s believed the universe is still expanding, so what’s currently observed may no longer be accurate.

Now, that’s the general idea about the universe’s (current) size, but what about age? As is stands, astronomers and scientists estimate the known cosmos is about 13.8 billion years old. How do they determine that? Primarily through observing how it expands, and also by looking at ancient objects. Said objects are old stars, so astronomers use telescopes to record the oldest stars in the known universe. From these observations, they’ve found globular solar clusters and stars between the ages of 10-14 billion years, so this allows scientists to form a proper number to the universe’s age.

Our Galaxy

Our Galaxy

Feeling small? It’s easy to get swept up in the sheer size of everything. So, let’s bring it down to something more local. Our galaxy, the Milky Way, has its own unique characteristics. Though we’re much smaller in comparison to said galaxy, it’s still our home.

Like the universe, the galaxy is about 14 billion years old, distinguished by its long “milky” spiral arms which have a diameter of around 150,000 light years. Within it is not only our star and solar system, but hundreds of billions of other stars. Each of those stars contains its own planets, likely counting in yet hundreds of billions more. That’s a big number! No wonder solar system puzzles are so hard!


As you can see, though things some large on Earth and our solar system a big place, it’s still quite small. The solar system vs. the galaxy is but one example of how frail and tiny our Earth is, and that’s nothing to say how we stack up compared to the sheer infinity of the known universe. The good news is it just means there’s a whole universe to learn about and explore! If technology allows, perhaps one day humans will venture into the stars. Then we’ll really know just how big (or small) we really are.

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