Universe Vs. Galaxy – The Difference Explained

Each of us occupies only a small space on a small planet awash in a sea of stars. When we look out at the sky at night, it’s no surprise we wonder about our place within the galaxy and, ultimately, the universe. To do so, we first need to understand a universe vs. a galaxy.

Universe Vs. Galaxy – The Difference Explained

What Is the Difference Between a Universe and a Galaxy?

As enormous as both of these objects are, galaxies simply can’t compare to the sheer size of the universe. Galaxies contain a seemingly countless number of stars, but the universe has so much more. Let’s break down each to understand their differences in full.

What Is a Galaxy?

A galaxy is a massive cluster of dust, gas, and stars that range on average somewhere between 3,000 and 300,000 light-years across. These celestial objects contain hundreds of billions of stars and most likely the same number of planets.

Galaxies are held together by gravity emitted by a supermassive black hole that sits in its center. All objects within a galaxy revolve around this black hole. There are four different types of galaxies, each characterized by their shape.

A meteor and galactic center of Milky Way galaxy
A meteor and galactic center of Milky Way galaxy seen from Hawaii Volcanoes National Park. (Image credit: Brocken Inaglory, CC BY-SA 3.0, via Wikimedia Commons)

The Earth is one tiny part of the Milky Way Galaxy, named because its central disc looks like a streak of milk across our sky in areas of little to no light pollution. It contains over 200 billion stars and is over 100,000 light-years across.

The existence of galaxies wasn’t made known until the early 20th century when Edwin Hubble determined the “nebulae” he was looking at were far outside our own galaxy. Since that point, scientists have been on a quest to discover just how many galaxies are out there.

Hubble Space Telescope nears Shuttle Endeavour
Hubble Space Telescope nears Shuttle Endeavour. (Image credit: NASA)

We can use the Hubble Space Telescope, New Horizons spacecraft, and the newly launched James Webb telescope to search for new galaxies. The latest estimates put the total number of galaxies at around 200 billion.

How Is a Galaxy Formed?

Galaxies likely form out of massive clouds of stellar gas and dust. These particles are affected by gravity and centrifugal forces, causing them to collapse and spin. Gasses and dust begin to collide and grow hotter and denser until stars are formed.

It’s not uncommon for galaxies to evolve over time and merge with other galaxies, forming even greater structures. Although we don’t know for sure, new galaxies may be still forming out on the edges of the universe.

Hubble Space Telescope have taken advantage of gravitational lensing to reveal the largest sample of the faintest and earliest known <a href=
Hubble Space Telescope have taken advantage of gravitational lensing to reveal the largest sample of the faintest and earliest known galaxies in the universe. (Image credit: NASA)

What Is the Universe?

The universe is the term we use to describe everything. It contains all of space, from the tiniest particle to planets, stars, and galaxies. This includes everything we can feel, measure, smell, hear, see, and detect.

The Earth is a microscopic piece of the grand canvas that the universe covers. At present, it’s impossible to guess how many other planets or stars are out there. We can only just estimate the number of galaxies based on recent findings from the New Horizons probe.

At best guess, scientists believe the universe first began 13.8 billion years ago. It is not stationary and has been expanding ever since that moment. This expansion is happening in every direction and is moving faster than we think it should. At an approximate speed of 67 kilometers per second per megaparsec, it’s covering a lot of space in short order.

This movement is causing most objects within the universe to travel away from each other, and there’s already a lot of distance between them. From what we can see, the current universe is over 93 billion light-years across, but that’s only as far as we can see.

How Was the Universe Formed?

The most widely accepted theory surrounding the creation of the universe is the Big Bang. 13.8 billion years ago, a massive explosion occurred at a single point in space. Within a second of that explosion, things had cooled enough for protons, neutrons, electrons, protons, and neutrinos to form.

Over time, gravity worked to bring these particles together, forming the first stars, galaxies, and planets. Out of everything created, at least one world developed life. 

Where Does Our Solar System Fit In?

Our Solar System is vast from our standpoint on Earth. The nearest planet to us is almost 25 million miles (38 million kilometers) away at its closest. From the Sun, the beginning of the Oort Cloud is some 90 billion miles (144 billion kilometers). That insane distance is still only 0.015 light-years.

This little section of space is a small piece of the 100,000 light-years in diameter Milky Way Galaxy. Let’s not forget that the universe itself is over 93 billion light-years in diameter.

What Can We See From Earth?

A man stands in a field, gazing up at the star-studded night sky.
A man stands in a field, gazing up at the star-studded night sky.

When we look out into the cosmos from Earth at night, we’re able to see five planets, the Moon, and approximately the 5,000 brightest stars nearest to us. All these stars are in a small section of the Milky Way galaxy. The only object we can see with the naked eye outside our galaxy is the Andromeda Galaxy, 2.5 million light-years away.

Final Thoughts

It wasn’t until the 20th century that we were finally able to begin to wrap our heads around how big our galaxy, let alone our universe, is. We’re now acutely aware that the Earth is a speck in a galaxy 100,000 light-years across and one of likely 200 billion galaxies in the universe. Our knowledge of the universe is limited only to the 46 billion light-years we can see in any direction.

About Noah Zelvis

Noah is a content writer who has had a love of all things astronomy for as long as he can remember.
When not reaching for the stars, you’ll likely find Noah traveling or running.