Galaxies are truly extraordinary objects.
It’s almost a cliche to talk about their size, scale, and distance, but, unless you really sit and work it out, it’s hard to comprehend just how alien these gigantic bodies of stars are to our everyday lives.
In this article, we’ve turned the remarkable statistics and facts that accompany these behemoths of the universe into a scale that is easier for our human brains to grasp.
Sit back, grab a coffee and work your way through our incredible list, or use the table below to jump to one that grabs your interest. Table Of Contents
- 1: Galaxies Are Unimaginably Far Away
- 2: We Can’t See Much of Our Own Galaxy – Even With a Telescope
- 3: Black Holes Lie at The Heart of Large Galaxies
- 4: There Are Different Classifications of Galaxy
- 5: The Milky Way is Flatter than Pizza
- 6: Galaxies Are Mostly Empty Space
- 7: But Stars Can Be Extremely Densely Packed in the Center of Galaxies
- 8: Our Home Galaxy is Huge
- 9: Our Solar System Orbits the Milky Way, Just Like Planets Orbit the Sun
- 10: The Milky Way Has Four Spiral Arms
- 11: The Milky Way is Small Compared to the Largest Known Galaxy
- 12: The Smallest Recorded Galaxy has Fewer Stars than Some Clusters
- 13: The Number of Galaxies and Stars is Practically Countless
- 14: But We’ve Only Named 36 Of Them
- 15: And This is the Farthest Galaxy of them All
- 16: Traveling at the Speed of Light Won’t Get Us There
1: Galaxies Are Unimaginably Far Away
It’s difficult to comprehend just how far away a galaxy is from our home planet, so it helps to have some context.
Let’s begin by shrinking our solar system down to ten meters, so that the farthest planet from the sun, Neptune is 10m away. At that scale, the nearest star, Alpha Centauri would be 53 miles away (85 km) away from the sun.
The nearest galaxy to the sun is a dwarf galaxy called Canis Major Dwarf Galaxy located 25,000 light-years away.
If we put Canis Major Dwarf Galaxy on the same scale as Neptune being 10 meters away, and the nearest star is 53 miles away, it would be a staggering 331,250 miles distant – about 1.5 times the distance to the moon!
Another way of thinking about the distance of galaxies is to consider light speed.
Light takes 0.25 seconds to get to us from the moon, 8 minutes from the sun, 4 years from the nearest star, and 25,000 years from the nearest galaxy.
The most distant object we can see without binoculars or a telescope is Andromeda Galaxy – light takes over 2.5 million years to reach us from there!
2: We Can’t See Much of Our Own Galaxy – Even With a Telescope
The most distant star we can see with the unaided eye is over 9,000 light-years away. In the northern hemisphere, the most distant star we can see is HR 7589 in Cygnus, it is 7,600 light-years away.
3: Black Holes Lie at The Heart of Large Galaxies
Every large galaxy is thought to have a supermassive black hole at the center of it. These can have a mass of over 4 billion of our sun… but that is still only 0.00003% of the galaxy’s total mass.
4: There Are Different Classifications of Galaxy
Galaxy is a generic term for a large collection of stars held together under their own gravity. It’s a rather loose, unscientific description but we do have more precise ways of classifying galaxies.
Edwin Hubble (whose name graces the Hubble Space Telescope) first proposed a classification method in 1926 which still forms the basis for what we use today.
The two main groups are elliptical and spiral galaxies. Elliptical galaxies are given an ‘E’ classification. The less round an elliptical galaxy is, the higher its number, so E3 ellipticals are more circular than E7s. There are no flatter ellipticals than E7, i.e. there are no E8s, E9s, etc.
Spirals are split into two groups, the standard spirals, given an ‘S’ catalog number, or barred spirals, which are given an ‘SB’ designation.
Regular spirals receive a higher second letter if they have more spirals, so an Sa has fewer spiral arms than an Sc. For barred spirals, a higher letter means the bar has less of a spiral, so an SBc galaxy has a straighter bar than an SBa one. See the diagram below for details.
Intermediates, between elliptical and spiral, earn the designation S0.
5: The Milky Way is Flatter than Pizza
Our galaxy is so flat that if it were the size of a 12″ pizza, it would be just 1/8th of an inch (3mm) thick.
This is because of how galaxies form which is in the same way as solar systems are created flat around their central star. Both come are born from clouds of gas with spinning angular momentum.
6: Galaxies Are Mostly Empty Space
Even with 100,000,000,000 (100 billion) stars in it, our Milky Way is mostly empty space – like all galaxies.
For most of its volume, stars are no closer together than every four light-years. If the sun was the size of a watermelon, the next closest one would be 12,000 miles (19,000 km) away, which is the equivalent of flying halfway around the world.
In other words, if we placed one watermelon at each of the poles, Earth would be as densely packed with watermelons as most of the Milky Way is with stars!
7: But Stars Can Be Extremely Densely Packed in the Center of Galaxies
In the galactic bulge near the heart of a galaxy, stars can be 10 million times more closely packed than in our sun’s region of the Milky Way.
Instead of every four light-years, that’s a star every three light-days! This is why the center of a galaxy is so bright when compared to the rest of it.
Using our watermelon example from above, we’d have to place one every six feet (1.9 meters) around Earth to match that density.
8: Our Home Galaxy is Huge
The Milky Way is about 100,000 light-years across and 1,000 light-years thick.
The central bulge is a seething ball of stars packed tightly together occupying an area of space 10,000 light-years in diameter.
9: Our Solar System Orbits the Milky Way, Just Like Planets Orbit the Sun
We orbit the Milky Way at a staggering speed. Every hour, our solar system moves 515,000 miles (828,000 km) on its orbital path around the galactic center.
Even at that speed, the galaxy is so huge that it takes us 230 million years to complete a single orbit. That’s such a long orbital period that dinosaurs had just begun to evolve last time we were at this point in our journey.
The Milky Way itself orbits a common center of gravity with the Andromeda Galaxy.
10: The Milky Way Has Four Spiral Arms
Our galaxy is a spiral type and has four spiral arms. The two main ones are called Perseus and Scutum-Centaurus, and the two spurs, Sagittarius and the Orion-Cygnus Arm.
We live in the Orion-Cygnus arm, which is why it’s also known as the Local Arm.
We’re roughly halfway between the center and the edge of the galaxy, about 26,000 light-years out from its heart.
11: The Milky Way is Small Compared to the Largest Known Galaxy
A galaxy called Alcyoneus is the largest known galaxy.
It is more than 3 billion light-years away and, at 16.3 million light-years from edge to edge, is 153 times the size of our own Milky Way.
To give a sense of its scale, consider that within 12 million light-years of Earth there are 23 other galaxies which themselves are more than 10,000 light-years across.
Alcyoneus could consume all of those and still have four million light-years of room for more.
12: The Smallest Recorded Galaxy has Fewer Stars than Some Clusters
A body of 1,000 stars, which makes it smaller than some globular clusters, such as the Great Hercules Cluster, is recognized to be the smallest recorded galaxy.
The dwarf Segue 2 orbits the Milky Way and is held together by dark matter.
13: The Number of Galaxies and Stars is Practically Countless
There are an estimated 100 billion galaxies in the universe. If each of these has 100 billion stars (on average), then we’re talking about 1×1022 stars in the universe. How big is that largely meaningless number?
Well, considering that Earth has about 1×1018 grains of sand, it means that for every single grain of sand on Earth, there are ten-thousand stars in the universe!
14: But We’ve Only Named 36 Of Them
For all of the billions of galaxies out there that we’ve observed and cataloged, less than forty galaxies have been named.
Less well-known names include Wolf-Lundmark-Melotte galaxy and Malin 1.
15: And This is the Farthest Galaxy of them All
The most distant galaxy yet recorded is GN-z11, it is about 32 billion light-years away! We are seeing it as it existed just 400 million years after the Big Bang.
It is so far away from us that the expansion of the universe is causing it to recede from our planet at practically the speed of light.
Light from our galaxy will have to travel twice the age of the universe to reach this galaxy.
16: Traveling at the Speed of Light Won’t Get Us There
Our galaxy is moving through space but, due to the nature of an expanding universe and their enormous distance, we can never hope to arrive at most of the galaxies we can see.
Even if could travel at the speed of light, only 3% of galaxies are within our reach. The other 97% are forever beyond us.
Galaxies are colossal, beautiful collections of staggering numbers of stars.
They are so far away that we can never hope to visit one. Heck, even if we had light-speed travel, we could only ever get to 3% of them.
Yet, our telescopes are like a time machine. A simple telescope for seeing galaxies will reveal dozens of these distant worlds to you, and you can marvel in your new-found facts as you observe them.
Written by Adam Kirk