Twenty light-years
These are the nearest stars, the first places any ship from the Sun would go. Within twenty light-years there are about eighty star systems and at least fifteen brown dwarfs, bodies too small to shine as stars, drifting on their own. Each one on the map stands on a stem that drops to the plane of the Galaxy, the flat disk in which the Milky Way’s stars circle: solid if the star lies above the plane, dashed if it lies below. The stems are there because a flat map lies. Tau Ceti, Epsilon Eridani and Epsilon Indi all sit eight to eleven light-years below the plane, while Alpha Centauri and Barnard’s Star lie almost in it.
What counts as a home
How full this map looks depends on what you are willing to call a destination, and the control at the top asks exactly that. The cautious answer is a star like the Sun, or one brighter: eighteen systems. Allow any ordinary star and the red dwarfs appear, the small dim stars that make up most of the Galaxy, and the count more than quadruples. Allow anything with mass, which is how a machine that needs only rock, ice and energy would see it, and the white dwarfs and brown dwarfs join.
Which answer is right is not an astronomical question. It turns on whether people will live in habitats they build, and whether they would choose to do so around a red dwarf. The first finding works through what each answer does to the pace of settlement.
The first wave
Press Launch. Every ship leaves the Sun at the same moment, and the systems light as each is reached.
It is natural to picture the neighborhood being settled star to star, each new settlement sending ships to the next. The arithmetic says otherwise. For a ship that cruises at a given speed, the fuel it burns depends on that speed and not on how far it goes: a star twenty light-years away costs no more to reach than Alpha Centauri. It only takes longer. So the Sun does not need stepping stones. By our estimate it could send a ship to every system on this map before the first new settlement had grown enough to build one of its own.
The order of arrival is then simply the order of distance. How long it takes depends on how fast a fusion engine can drive a ship that must also stop at the far end, and that is not known. Our middle estimate is about three percent of light speed. At that pace the first ship reaches Alpha Centauri in about a century and a half, and the last reaches the edge of this map in under seven hundred years. If engines perform as their designers hoped, halve those times. If they barely work, triple them.
What limits the reach is not fuel. It is whether a machine can fly for centuries and still work when it arrives, and nobody has tested that.
Nothing here stays put
Let the stars drift and the map comes apart. Every star has its own motion, and over a hundred thousand years the neighborhood replaces most of its members. Barnard’s Star swings past in under ten thousand years. Alpha Centauri keeps closing for another twenty-eight thousand. Ross 248, a red dwarf ten light-years away today, will pass at three light-years in about thirty-six thousand years and for a while be our nearest neighbor.
A first wave would be over long before any of this mattered; in a few centuries the stars barely move. But it changes how to think about the place. The Sun’s neighbors are not a fixed set of destinations. They are whoever happens to be passing, and settlements planted around them will, over tens of thousands of years, be carried off in every direction. On the scale of the whole Galaxy that scattering becomes the main story.
How this map was made
Star positions, distances and motions come from the AT-HYG catalogue, which combines measurements from the Gaia and Hipparcos space telescopes with older surveys. Brown dwarfs and the faintest red dwarfs come from the SIMPLE archive of published measurements. Stars that orbit each other share one marker. Alpha Centauri moves as its center of mass moves, using the 2021 orbit solution by Akeson and colleagues.
The clock carries each star forward in a straight line at its measured velocity, which holds well over a hundred thousand years. Seventeen objects, most of them brown dwarfs, have no measured speed along our line of sight; their paths use sideways motion only, and their cards say so. Stars now outside the map enter it only if their full velocity is known, so a few faint arrivals are certainly missing. The brown dwarf census is incomplete, and surveys are still finding them.