Topics Space and the universe

How far away is the nearest star?

Apart from the Sun, the nearest star is Proxima Centauri, about 4.2 light-years away. That is roughly 40 trillion kilometers, or about 25 trillion miles. Proxima belongs to the Alpha Centauri system, which also holds two brighter stars, one similar to the Sun and one a bit cooler, a little farther out.

What makes the number interesting is how hard it is to feel. In units of the Earth-Sun distance, Proxima is roughly 270,000 times as far. Light from it takes over four years to reach us, so we see it as it was four years ago. Astronomers found the distance by parallax, the tiny apparent shift of a star as Earth moves around its orbit. Proxima is also a small, dim red dwarf, so you cannot see it without a telescope.

An episode on bre, whose hosts are AI and can be wrong, would walk through the distance, the measuring trick, and why even our closest neighbor is out of practical reach. You can press Talk and ask a question at any point, such as how long a trip would take.

What a bre episode would cover

An outline of the episode bre would make for this question. Every episode is written fresh when you ask, so yours will differ.

  1. The short answer: Proxima CentauriWhich star is nearest, how far it is in light-years and kilometers, and how it relates to Alpha Centauri.
  2. What a light-year really measuresA light-year is a distance, not a time: how far light travels in a year. That is why Proxima's light is over four years old when it arrives.
  3. Measuring with parallaxAs Earth circles the Sun, nearby stars seem to shift against distant ones. That small angle, plus geometry, gives the distance.
  4. Picturing the scaleShrink the Earth-Sun distance to one centimeter and Proxima lands about 2.7 kilometers away. Space between stars is mostly empty.
  5. A dim red neighborProxima is a small red dwarf, far too faint to see by eye. Astronomers have found at least one planet orbiting it.
  6. Could we ever go there?Our fastest spacecraft would need many thousands of years. Researchers have discussed concepts for faster probes, but none exist yet.

How the episode might open

A sample exchange between two of bre’s AI hosts, bre and Cal. Both are AI; this is written by AI, as every bre episode is.

  1. breAI host

    Okay, the question sounds simple. How far is the nearest star? And the answer is: not the Sun, obviously, the next one. Proxima Centauri, about four point two light-years away.

  2. CalAI host

    Which is a number that means nothing to me until someone translates it. Four light-years. Is that close? It sounds close.

  3. breAI host

    It's the closest there is, and it's still enormous. The light reaching us tonight left it a little over four years ago.

  4. CalAI host

    Okay, that stings. So when I look at it, I'm looking at the past.

  5. breAI host

    Always, a little. And nobody flew out there with a tape measure, so here's the part nobody tells you: we got that distance from Earth, using nothing but geometry.

  6. CalAI host

    Hold on, how does that actually work? How does a tiny shift in a star's position turn into a distance? Is it like holding up a finger and blinking one eye, then the other?

  7. breAI host

    Exactly that. Your finger jumps against the wall behind it. Closer things jump more. Swap your eyes for Earth on opposite sides of its orbit, and the wall for faraway stars.

  8. CalAI host

    So the baseline is the whole orbit. That's a big pair of eyes.

  9. breAI host

    It is. So let's start with that orbit, and then we'll get to what happens if you try to fly there.

Questions people also ask

What is the closest star to Earth besides the Sun?
Proxima Centauri, a small red dwarf about 4.2 light-years away. It is part of the Alpha Centauri system, which has two other stars slightly farther out, at roughly 4.4 light-years. Proxima is too faint to see without a telescope.
Is Alpha Centauri the nearest star?
Not quite. Proxima Centauri, part of the Alpha Centauri system, is the nearest star. The system as a whole is the nearest star system. Its two brighter stars, Alpha Centauri A and B, are a little farther away than Proxima.
How long would it take to reach the nearest star?
With the fastest spacecraft we have built so far, many thousands of years. Light itself takes a bit over four years. Ideas for much faster probes exist on paper, but nothing like them has been built or flown.
Can you see the nearest star with the naked eye?
Proxima itself, no, it is too dim. But the brighter Alpha Centauri A and B appear together as one bright point of light. They are visible from latitudes roughly south of 29 degrees north, so they are well placed for the Southern Hemisphere.

Related topics

More: all 300 topics, space and the universe, or the longer reads on /learn.

bre’s hosts are AI, and every episode is generated, so they can be wrong: check anything that matters. This page outlines what an episode would cover. It is for interest and learning, not medical, financial or legal advice.