How it works

No single ruler works for space. Each step outward is so much bigger than the last that the only sensible way to count is in powers of ten, with a new unit every few steps.

From here	Distance	In other words
Across the Earth	12,742 km
Earth to the Moon	384,400 km	30 Earths side by side
Earth to the Sun	149.6 million km	1 au, or 390 times the distance of the Moon
Sun to Neptune	4.5 billion km	30 au
Sun to the edge of the solar wind	about 18 billion km	about 120 au
Sun to the nearest star	40 million million km	4.25 light years, or 269,000 au
Sun to the middle of the Milky Way		about 26,700 light years
Milky Way to the Andromeda Galaxy		about 2.5 million light years
Here to the furthest light we can see		about 46 billion light years

Two things stand out.

The first is how much room there is between the planets and the stars. The planets take up the innermost 30 au. The nearest star is nearly nine thousand times further away than Neptune. If comets really do fill a cloud out to tens of thousands of au, as their orbits suggest, then most of the Sun’s territory is that cloud, and nobody has ever seen any of it.

The second is that the jumps do not get smaller. From the Solar System to the nearest star is a factor of about ten thousand. From there to the far side of the galaxy is another ten thousand or so. From our galaxy to the next large one is a factor of twenty-five, which sounds modest until you remember what it is twenty-five times.

The last line of the table needs a note. The universe is 13.8 billion years old, yet the furthest light we can see comes from matter that is now about 46 billion light years away, because space has kept stretching while the light was on its way.