The Andromeda Galaxy is one of two large spiral galaxies near our Milky Way Galaxy, the other being the Triangulum Galaxy. Andromeda is closer to us than Triangulum is.
So how far away is the nearest galaxy to our own?
To answer the answer to this question, it’s necessary to understand distances in space and the size of our galaxy. Let’s start with Earth, which is about 8,000 miles (13,000 km) in diameter. Understanding how large our planet is takes us to the next step.
Earth is about 93,000,000 miles from our sun, or about 11,700 times the diameter of the Earth. This distance is called one astronomical unit, or AU. Astronomical units are often used for explaining distances in space, particularly within our solar system.
The speed of light, and a light year
Next, the speed of light is important to understand. Light travels about 186,000 miles (300,000 km) per second. Light takes a little more than eight minutes to travel from the sun to Earth. Something traveling at light speed could race all the way around Earth, which is about 25,000 miles or 40,000 km in circumference, about 7.5 times in one second.
The Triangulum Galaxy is the third-largest member of the Local Group of galaxies, which includes our Milky Way and Andromeda galaxies.
Distances in space
Here are the five planets in our solar system that are further away from the sun than we are. Ranges vary due to orbits being elliptical:
- Mars ranges from 1.4 to 1.7 AU from the sun.
- Jupiter ranges from 5.0 to 5.5 AU.
- Saturn ranges from 9.0 to 10.1 AU.
- Uranus ranges from 18.4 to 20.1 AU.
- Neptune ranges from 29.8 to 30.4 AU.
Some other solar system objects that are further away from the sun include:
- Dwarf planet Pluto ranges from 29.7 to 48.9 AU from the sun.
- Dwarf planet Eris ranges from 38.2 to 97.7 AU.
- Dwarf planet Sedna ranges from 76.4 to 937 AU.
Sedna takes about 11,400 years to orbit the sun, and at its furthest point, light from the sun would take 5.4 days to reach it. Luckily it’s closer to us right now, at around 90 AU, or we wouldn't know about it. It’s thought that there are probably hundreds of dwarf planets in our solar system, or possibly thousands, and we only know of a small fraction of them.
One light year equals to 63,241 AU. Therefore our solar system, if it is defined by the orbits of known planets and dwarf planets, is far smaller than this, not even 2% of one light year.
The nearest star
The nearest star that isn’t our sun, Proxima Centauri, is 4.24 light years away. This is about 267,000 AU. The distance, 4.24 light years, means it would take about four and a quarter years for light from our sun to reach the closest one outside of our solar system. This vast distance to the closest star not in our solar system is about 24.9 trillion miles (40.1 trillion kilometers).
An artist's depiction of Proxima Centauri reflects that although called a red dwarf, the color is actually orange. A majority of stars in our galaxy are thought to be red dwarfs, which are considerably less massive than our sun, which is a yellow dwarf. Proxima Centauri, despite being the closest star to our solar system, is not visible to us from Earth without the aid of a telescope.
The size of the Milky Way
The Milky Way likely has billions of solar systems. It’s unknown how many have planets have living beings. In total there are certainly more than 100,000,000,000 (100 billion) stars, and possibly several times that many.
Our little solar system sits about halfway between the center of our galaxy and the edge. In total, our galaxy, of which our solar system comprises a very tiny piece, is estimated to be 100,000 to 120,00o light years across or possibly more. This means a diameter of at least 6,324,100,000 (over six billion) AU.
Back to the original question
The information above is to provide a better understanding of the answer to the question, and to have more of an idea of what these distances mean. It's easy get lost quickly with such vast numbers, as they’re difficult for anyone to comprehend.
The Milky Way is part of a system of galaxies, in which other smaller nearby galaxies are gravitationally bound to it. In total there are at least fourteen of these smaller satellite galaxies. The closest is called Canis Major Dwarf, which scientists believe is in process of being pulled apart and made a part of the Milky Way. It is located just 25,000 light years away.
Whether Canis Major Dwarf truly counts as a dwarf galaxy is disputed, and the next-closest dwarf galaxy, which is also part of the Milky Way system, is the Sagittarius Dwarf Spheroidal Galaxy, located 70,000 light years from Earth.
Of the small satellite galaxies thought to be associated with, and orbiting, the Milky Way, the one furthest from us is 2,250,000 light years away. This is between 13 and 22 times the diameter of the Milky Way, depending on which of the various estimates of the size of our galaxy we're going by.
The closest large spiral galaxy similar to the Milky Way is the Andromeda Galaxy, which is very similar to our galaxy, and almost the same size. Andromeda is about 2,500,000 light years away, a distance 15 to 25 times that of the diameter of the Milky Way, and it probably has at least 19 smaller galaxies nearby that are orbiting it.
Of Andromeda’s associated dwarf galaxies, ten or so are closer to us than Andromeda itself. The closest galaxy to us that is not part of the Milky Way system is a dwarf galaxy associated with Andromeda called NGC 185, and it is slightly more than 2,000,000 light years away.
One more spiral galaxy is "nearby"
Our Milky Way, the Andromeda, and one other spiral galaxy and their satellites comprise the Local Group of at least 54 galaxies (including the three and their satellites). The third spiral galaxy is the Triangulum Galaxy, pictured above, which is smaller (about half the diameter), compared with Milky Way and Andromeda.
Triangulum is about 3,000,000 light years away. The Local Group itself spans about 10,000,000 light years. The Local Group is part of the Virgo Supercluster of at least 100 groups, the Local Group being just one of those. And this supercluster is one of millions that we know of.
Also, everything is constantly in motion. The Milky Way and Andromeda are on trajectories to collide with one another in 3.75 billion years or so.
Okay, so the original question wasn’t so easy to answer. But now you know how complex this subject is.
Milky Way Galaxy look-alike:
Located 30 million light years away, NGC 6744 is the name of a galaxy that scientists say looks more like our Milky Way than any others located near enough to get a photo like this.