Galaxy Facts

GALAXY FACTS

The home of interesting galaxy facts for kids and adults.

Interesting facts about galaxies.

Galaxies can be divided into three shape classifications.

Some of the galaxies within the local group

What is a galaxy?

What is a galaxy? Well, a galaxy is a collection of dust, gas, dark matter, stars and of course planets that are all bound by gravity. The word galaxy comes from the word galaxias (Greek), which means "milky".

IHowever, if you want the official definition. 

A galaxy is a gravitationally bound collection of stars whose properties cannot be explained by a combination of baryons and Newton’s laws of gravity.

Did you know?
Up until the new definition Pluto was classed as a planet within our solar system. It is now defined as a Dwarf planet.

Photograph of the milkyway galaxy

10 Facts about galaxies you didn't know.

1. Galaxies have their own satellites

Our galaxy, as an example, has smaller galaxies that are in orbit around it. These 'satellite galaxies' are called dwarf galaxies and they contain several billion stars each. That's a lot of stargazing!

Did you know?
There are galaxies even smaller than dwarf galaxies, called hobbit galaxies.


Photograph of the night sky
Photo of the andromeda galaxy

2. The Andromeda galaxy is not our closest neighbour

The Canis Major Dwarf Galaxy is 100 times closer to us than the Andromeda galaxy is. The Canis Major galaxy is 42,000 light-years away from the galactic centre, and it is also a satellite dwarf of the Milky Way (the galaxy where we live).

Did you know?
Canis Major is Latin for ‘greater dog’.

3. The Milky Way is colliding with another galaxy

Our very own Milky Way is currently in the process of colliding with another, smaller, galaxy. This smaller galaxy is called the Sagittarius Dwarf elliptical galaxy, and it is one of our satellite galaxies. The Sagittarius Dwarf Galaxy is roughly 78,300 light-years away.

Did you know?
These two galaxies have ‘met’ 3 times before, the last time being 1 billion years ago.


Photograph of the milky way galaxy
Stature of Immanuel Kant against green tree

4. Galaxies are ‘island universes’?

The Prussian eighteenth-century philosopher Immanuel Kant was one of the very first people in the world to theorise that our galaxy was not the only one of its kind in the universe. Kant thought of galaxies as being self-contained universes – coining the term 'island universe' to describe a galaxy.

Did you know?
Kant acknowledges English astronomer Sir William Herschel as a source of inspiration.

5. Do you know why our galaxy is called the Milky Way?

We know that galaxy comes from the word galaxias (Milky), so what about the rest? One of the earliest recorded uses of 'Milky Way' is in Geoffrey Chaucer's poem 'The House of Fame'. He likened our galaxy to a celestial roadway. The Milky Way.

Did you know?
The Milky Way makes a full rotation every 200 million years.


Pencil sketch of Geoffrey Chaucer
Photograph of shooting star in night sky

6. Many galaxies are speeding away from us

Because the universe is expanding, most other galaxies within it are moving away from us. They are not all moving at the same speed either; galaxies that are further from us are pulling away faster than the ones closest to us.

Did you know?
It is thought that there are approximately 100 billion galaxies in the observable universe.


7. There is a black hole in the centre of the Milky Way

Although you can't see the black hole that resides at the centre of our galaxy, if you have ever looked at the constellation named Sagittarius, the centaur archer, then you have been gazing in the right direction.

Did you know?
Most galaxies contain a black hole, and they are all consistently 1/1000th the mass of the galaxy they call home.


Photograph of a telescope in shadow against the night sky
Photograph emulating the spin of stars as they move across the sky

8. Galaxies rotate much fast than predicted

Galaxies spin faster than previously predicted, based solely on the gravity of their stars. Astronomers believe now that the additional gravitational pull is emanating from dark matter.

Did you know?
Dark matter neither reflects nor emits light and is thought to make up around 1/4th of the total energy density of the universe.


9. Apples and oranges – a galactic size comparison

If the stars of a galaxy were the size of oranges, they would be separated from each other by around 3,000 miles. However, if galaxies were the size of apples, they would be mere metres away from each other.

Did you know?
When galaxies collide, because of the vast distances between them, stars rarely collide.


Photograph of some apples and oranges lying on tartan blanket
Photograph of a black Ellipsoid diagram

10. Our galaxy is merging with another

In roughly 4 billion years, our galaxy is going to merge with the Andromeda galaxy. The result of this merger, which will take a hundred million years, at least – will be an ellipsoidal galaxy, whereas right now the Milky Way is a spiral galaxy.

Did you know?
The coming ellipsoidal galaxy has been nicknamed ‘Milkomeda’.


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