How Far is the Closest Star?

Hubble image of Proxima Centauri, the closest star to the Sun. NASA

Hubble image of Proxima Centauri, the closest star to the Sun.

The simple answer is that the Sun is the closest star to Earth, about 93 million miles away, but that might not answer your question. Outside of our Sun, our system's nearest neighbor is Alpha Centauri. This isn't a single star, it's actually a triple-star system — three stars bound together by gravity. Alpha Centauri A and B are two bright, closely orbiting stars with a distant, dim companion named Proxima Centauri. The inner binary appears to the unaided eye as a single star, the third brightest in the night sky, but it lies 4.37 light years from the Sun. Faint Proxima Centauri is the one that claims the honor of being our true nearest stellar neighbor at only 4.24 light years away.

It’s difficult to conceptualize such vast distances, but a popular analogy sets the Sun at the size of a grapefruit. If you wanted to get from your grapefruit-sized Sun to a grapefruit-sized Alpha Centauri system, you would have to travel about 2,500 miles, which is about the distance from coast to coast on the continental United States. And that’s just to the Sun’s closest neighbor!

Does that means it's too far for our Earthly reach? Maybe not. There's a plan in the works, funded by Breakthrough Starshot, to send tiny smartphone-size probes to the Alpha Centauri system. It would be a one-way trip that would take these lightsail-powered spacecraft 20 years. Why go such a long way? Well, for one, astronomers have found a planet orbiting Proxima Centauri. While it's unlikely it would be habitable, boy would that be a fun and informative planet to visit. (Not that it would be an easy trip.)

But Proxima Centauri is only currently the closest star. The Sun, the Alpha Centauri system, and other nearby stars all move around the Milky Way over time, and they approach and pass each other as they travel. In another 10,000 years or so, the closest star will be something else.

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