Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.
where, for simplicity, celestial objects are shown in unrealistically close proximity—like Jupiter is just down the hall from Mars.
As we all know, the planets of the solar system are actually really far apart, even relative to their huge size. In Sweden's 1:20,000,000 to-scale solar system model, Earth and Venus are just ~2 feet in diameter, yet over a mile apart. In other terms, they're several thousand "Earth-widths" apart:
Horizontal distance not to scale, wouldn't fit on screen.
And we all know that's just the start of it: the stars are incredibly far apart. Finland also has a to-scale model of the solar system, but it's 150x more condensed than Sweden's at 1:3,000,000,000.[1] Its model of our sun, Sol, is just ~1.5 feet in diameter.
Its model of the nearest star, Proxima Centauri, is in Australia.[2]
Horizontal distance obviously not to scale.
That's even crazier than Earth-Venus, especially considering a "Sun-width" is ~865,000 miles.
So if we keep going bigger, what happens then? What about galaxies?
That image is to scale. If the Milky Way were a typical US suburban home, Andromeda would be a McMansion 3 blocks down the road.[3]
And while many people know that Earth's Moon is not terribly close to Earth:[4]
Again, image here is to scale.
How many know that the Milky Way's "moon", the Large Magellanic Cloud, is about as close as Earth's Moon is often misleadingly depicted?
To scale.
There are some interesting implications here; in particular, if your star-faring civilization can colonize the entire Milky Way, you can probably make it over to Andromeda without much more difficulty.[5]
And indeed, you wouldn't stop there either. The next step up from "galaxy" is a "galaxy group", and those can be quite close (relatively speaking) too:
To scale, including the galaxies, which are slightly bigger than a pixel in the full image.
And indeed, Humanity happens to be in a more exurban part of space. If we look at the "nearby" Virgo Cluster[6] ~54 million light-years away (merely 620 Milky-Way-widths), it's quite dense:
Left and right images are each to scale.
If the Milky Way is a typical suburban house, and Andromeda is a McMansion 3 blocks down the street, then the Virgo Cluster is a city center just a 6-mile drive away.[7]
If you're curious, here's an interactive widget for checking out distances in relative object-widths. You can see at the bottom that celestial objects' distances in object-widths vary by 7 orders of magnitude;[9] that's what I mean by "outer space is not consistently big".
Estimates of the size of the Milky Way vary considerably; it's hard to measure from the inside. I am using, for both the Milky Way and Andromeda, estimates of the diameter of what would actually look like part of the galaxy in a typical telescope photo (D25 brightness cutoff), as opposed to how far out outer-disc stars in its gravity extend. (Milky Way: 87,400 light years; Andromeda: 152,000 light years)
One could argue that actually the "true" diameter of a galaxy ought to include not only outer stars, but also its dark matter halo. If we did that, Andromeda would only be ~1.3 halo-widths away! Considering dark matter is believed to be >90% of the Milky Way's mass, you can understand why it and Andromeda are fated to merge.
Though it's worth noting that "dark matter halo" is a historical misnomer. Dark matter was first noticed outside of galaxies, but it's now believed that dark matter exists as more of a spherical cloud, densest in the center, where the normal (baryonic) matter is densest too.
Unless there's something wacky about intergalactic space I'm not aware of? I don't really think it's necessary to resupply at star systems along the way—you only really need to accelerate (and decelerate) once—but even if you needed to, there are stars out in intergalactic space you could use.
One could complain that it's unfair to compare "solid" objects like stars to mostly empty objects like galaxies. Fun fact, if we take the "mostly empty" version of a star—a full solar system including its Oort cloud, with a reasonable density cutoff for the Oort cloud—then Proxima Centauri is only ~3 to 17 solar-system-widths away! (we don't know exactly how big or dense Oort clouds are)
When we say "space is big", it's partly meant as a correction to images like this:
Wikimedia source.
where, for simplicity, celestial objects are shown in unrealistically close proximity—like Jupiter is just down the hall from Mars.
As we all know, the planets of the solar system are actually really far apart, even relative to their huge size. In Sweden's 1:20,000,000 to-scale solar system model, Earth and Venus are just ~2 feet in diameter, yet over a mile apart. In other terms, they're several thousand "Earth-widths" apart:
Horizontal distance not to scale, wouldn't fit on screen.
And we all know that's just the start of it: the stars are incredibly far apart. Finland also has a to-scale model of the solar system, but it's 150x more condensed than Sweden's at 1:3,000,000,000.[1] Its model of our sun, Sol, is just ~1.5 feet in diameter.
Its model of the nearest star, Proxima Centauri, is in Australia.[2]
Horizontal distance obviously not to scale.
That's even crazier than Earth-Venus, especially considering a "Sun-width" is ~865,000 miles.
So if we keep going bigger, what happens then? What about galaxies?
That image is to scale. If the Milky Way were a typical US suburban home, Andromeda would be a McMansion 3 blocks down the road.[3]
And while many people know that Earth's Moon is not terribly close to Earth:[4]
Again, image here is to scale.
How many know that the Milky Way's "moon", the Large Magellanic Cloud, is about as close as Earth's Moon is often misleadingly depicted?
To scale.
There are some interesting implications here; in particular, if your star-faring civilization can colonize the entire Milky Way, you can probably make it over to Andromeda without much more difficulty.[5]
And indeed, you wouldn't stop there either. The next step up from "galaxy" is a "galaxy group", and those can be quite close (relatively speaking) too:
To scale, including the galaxies, which are slightly bigger than a pixel in the full image.
And indeed, Humanity happens to be in a more exurban part of space. If we look at the "nearby" Virgo Cluster[6] ~54 million light-years away (merely 620 Milky-Way-widths), it's quite dense:
Left and right images are each to scale.
If the Milky Way is a typical suburban house, and Andromeda is a McMansion 3 blocks down the street, then the Virgo Cluster is a city center just a 6-mile drive away.[7]
In that sense, space ain't so big after all![8]
If you're curious, here's an interactive widget for checking out distances in relative object-widths. You can see at the bottom that celestial objects' distances in object-widths vary by 7 orders of magnitude;[9] that's what I mean by "outer space is not consistently big".
Finland does have another one at 1:1,000,000,000, only 50x more condensed.
Yes there's actually a to-scale model there. It's ~3 inches in diameter.
Estimates of the size of the Milky Way vary considerably; it's hard to measure from the inside. I am using, for both the Milky Way and Andromeda, estimates of the diameter of what would actually look like part of the galaxy in a typical telescope photo (D25 brightness cutoff), as opposed to how far out outer-disc stars in its gravity extend. (Milky Way: 87,400 light years; Andromeda: 152,000 light years)
One could argue that actually the "true" diameter of a galaxy ought to include not only outer stars, but also its dark matter halo. If we did that, Andromeda would only be ~1.3 halo-widths away! Considering dark matter is believed to be >90% of the Milky Way's mass, you can understand why it and Andromeda are fated to merge.
Though it's worth noting that "dark matter halo" is a historical misnomer. Dark matter was first noticed outside of galaxies, but it's now believed that dark matter exists as more of a spherical cloud, densest in the center, where the normal (baryonic) matter is densest too.
Are you one of today's lucky 10,000 to learn that you could fit every planet in the Solar System between the Earth and the Moon?
Unless there's something wacky about intergalactic space I'm not aware of? I don't really think it's necessary to resupply at star systems along the way—you only really need to accelerate (and decelerate) once—but even if you needed to, there are stars out in intergalactic space you could use.
The dense center of the Virgo Supercluster which the Milky Way and Local Group (and M81 Group) are also a part of.
And the Virgo Supercluster would be the metropolitan area.
Though I have been informed that "54 million light-years" is a longer distance to walk than 6 miles.
One could complain that it's unfair to compare "solid" objects like stars to mostly empty objects like galaxies. Fun fact, if we take the "mostly empty" version of a star—a full solar system including its Oort cloud, with a reasonable density cutoff for the Oort cloud—then Proxima Centauri is only ~3 to 17 solar-system-widths away! (we don't know exactly how big or dense Oort clouds are)