Solar System, Galaxy, & Universe: Definitions & Difference

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  • 0:02 The Universe
  • 1:32 Galaxies
  • 2:51 The Solar System
  • 4:07 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

Want to learn what the universe, galaxy, and solar system are as well as some cool facts about each one? This lesson will give you an overview of what these three things are in a relatable fashion.

The Universe

Let's imagine that we have a magical satellite that is able to snap pictures as it rotates outside and around our universe, the totality of all that exists, the cosmos. This satellite is called Moogle Universe. It constantly uploads stuff it snaps pictures of onto the web.

As you log on to this website, you'll see on your screen that you're able to use a mouse to zoom in on different parts of the universe (please see the video at 00:29). Additionally, some user has already tagged a bunch of stuff for us so we only have to mouse over to learn cool information. Before we zoom in to more detailed aspects of the universe, let's mouse over the tag at the center of the universe to see what it reads (please see the video at 00:49). The universe is flat and is composed of 4.6% atoms, 24% cold dark matter, and 71.4% dark energy.

There's also another tag to the left; let's mouse over to learn a bit more about our universe (please see the video at 01:06). The entire universe should not be confused with the observable universe, which is the part of the universe we can actually see.

Finally, there's one other tag at the far right of the screen. If you move your mouse to the right, you'll see that it tells us that the universe was once contained in an infinitely compact state and it has expanded ever since the Big Bang (please see the video at 01:20).


OK, now let's zoom in on the observable universe (please see the video beginning at 01:34). As we zoom in, more and more galaxies become apparent in all their splendor. A galaxy is a large collection of stars, gas, and dust kept together by gravity. If the universe is like our planet, then a galaxy is like a country contained within the planet.

There are three tags for the galaxies on the screen we should look at. As we mouse over one of them, it explains that although there may be close to 200 countries in the world, it's estimated there could be upwards of hundreds of billions of galaxies in the observable universe (please see the video at 02:03).

See that tag up at the top? Let's get to that one next (please see the video at 02:20). When 'galaxy' is written in lower case, it is meant as a general term, but when it is capitalized, it refers to our Galaxy, the Milky Way Galaxy, where our sun and Earth reside.

Finally, don't forget the tag on the right. As we mouse over, it tells us another new fact (please see the video at 02:36). Galaxies come in all sorts of different shapes and sizes. As shown on your screen, they can be elliptical, lenticular, spiral, dwarf, and irregular:

Different shapes of galaxies
image showing outer space with different galaxy shapes

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