Difference Between Galaxy and Universe

Galaxy vs Universe
 

If someone says that the difference between galaxy and universe is in the size of each, that statement is completely true. Have you ever thought about that? We human beings frequently talk about our universe, but do we understand what the term really means? Giant strides made by science in the last few decades have meant that we perhaps know a lot more about our neighbors and cousins (earth’s) than our ancestors. However, what we know is a still miniscule in comparison to what really exists. We may talk about the universe and galaxy, but these words are confusing for many as they think of these words as synonyms, and even use them interchangeably. Reality is totally different. Let us take a closer look.

What is a Galaxy?

A galaxy is a huge system containing lots of stars and dark matter that are gravitationally bound. The size of galaxies varies from very small (containing ten million stars) to giant galaxies that may contain up to hundred trillion stars. The sun is just one of the stars in our galaxy known as Milky Way. For those who think of earth as being of some significance, let me tell you that our solar system, which includes our sun (yes ours) and other 7 planets is no more than an oasis in our galaxy, which in itself is like a tiny spot in the universe.

Milky Way is the name of the galaxy that our solar system hangs on. This Milky Way is just one of innumerable galaxies in the universe. To be frank, there are some 100 billion stars, many of which are many times larger than our sun. The star that is closest to the sun is about 4 light years away, which is considered as a very short distance in galactic terms. Now, this Milky Way Galaxy, which has about 100 billion stars, is known as a small galaxy. Our neighbor, the Andromeda Galaxy is much larger than our Milky Way. Depending on their appearance, these galaxies are divided into three main categories as elliptical, spiral and irregular.

As the name suggests, elliptical galaxy is elliptical in shape. Or, in other words, these types of galaxies are elongated. Then, the spiral galaxies are in the shape of a spiraling pinwheel. Irregular galaxy is a galaxy that does not have a distinctive shape like the two former types, elliptical and spiral galaxies.

In the picture given below, you can see light specks. As NASA says each of these specks is a galaxy.

What is the Universe?

The universe is vaster than we can ever imagine. It is a combination of all the galaxies. So, it would be correct to say that our solar system that holds so much significance for us and our planet is no more than a tiny spec in a huge universe that exists well beyond our solar system and the Milky Way. Thus, it is clear that the universe is much, much larger than all the galaxies combined together. It is believed that there are about 200 billion galaxies in the Observable Universe. Observable Universe is the part of universe that we can observe from the earth.

Just imagine million of such stars in our galaxy, and then think of billions of galaxies existing in our universe, and you will come to realize of the size of the universe. With the tools available and our knowledge, it is impossible even to surmise the size of the universe. May be in times to come, we would be better off to predict the size of this universe.

What is the difference between Galaxy and Universe?

• The differentiation between a galaxy and universe begins and ends with size only.

• Our solar system is a part of our galaxy, which contains millions of stars like our sun.

• There are billions of such galaxies in the universe.

• It is impossible to conjecture about the size of the universe with current knowledge and tools.

• It would help to think of our galaxy, the Milky Way, as just a speck in the Universe.

So, our earth is a part of the solar system. Our solar system is a part of our galaxy, the Milky Way. Milky Way has billons of stars. Once billions of galaxies like the Milky Way come together, that is known as the universe.

Images Courtesy:

1. Hubble eXtreme Deep Field “XDF” (2012) view via Wikicommons (Public Domain)
2. Constituent spatial scales of the observable universe by Andrew Z. Colvin (CC BY-SA 3.0)