The introduction begins like this:
'Space,' it says, 'is big. Really big. You just won't believe how vastly hugely mindbogglingly big it is. I mean you may think it's a long way down the road to the chemist, but that's just peanuts to space."
So, what part of Douglas Adams' work is non-fiction?
Let's take the size and distance comparisons of Earth and Sun down to something you can see.
Let's use a basketball to represent the sun. At this scale, you would need to find a fine grain of sand to represent the Earth.
Okay, now that you have a good idea of the size difference between the Earth and sun, how about distance?
Take your grain of sand, and walk about three blocks up the street. Use the standard block size if you happen to live on one of those fancy elongated blocks. Turn around, and look back at the basketball sun. That's approximately the distance of Earth to the sun at this scale.
It takes eight minutes for the light leaving the sun to reach Earth, so if it took you eight minutes to walk those three blocks, you were walking at approximately the speed of light. Now you have to use your imagination to realize that there is nothing but empty space between the Earth and sun, except the orbits of two other grains of sand.
Now take a second basketball, and walk for four years at the same pace that it would've taken you to walk the original three blocks in eight minutes. Yes, four years. That's the distance, in light years, it is to the closest star from our own. That is to say, it takes light four years to travel from the closest star to us.
If we could travel at the speed of light, it would only take four years to reach that star. If we could travel 1/10th the speed of light, it would take us 40 years, or almost an entire life-span. But we can't even travel that fast, unless we could map out a trajectory around the sun and biggest planets to sligshot us faster... and we'd still have to work on that being able to sligshot us in the right direction.
Once again, let's use our imagination to realize that, except for a few scattered grains of sand, a couple of baseballs, and maybe a comet or two, that there is, once again, nothing but empty space between those two basketballs.
Can you even see that grain of sand that we call Earth?
How small does that make you feel?