This article says it will pass by the star in about 40,000 years. However, my quick and dirty calculation shows that Voyager will only be about a few light years away in 40,000 years, still quite a ways from any star. How should this be reconciled?

Bottom line, When will Voyager 1 actually encounter AC +79 3888?

Upon further inspection, this article appears to be the source.

  • $\begingroup$ This paper is a more... archival source; it cites this paper for the "40,000 year" figure, but the only copy I can find is incomplete :( . At the very least, both are journal articles, meaning that the figures were peer-reviewed, and that counts for something (i.e. it's not just a flubbed calculation by some PR person... but it could still be a flubbed calculation by the authors). $\endgroup$
    – user29
    Sep 13, 2013 at 20:59
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    $\begingroup$ Voyager 1 is currently moving at about 17 km/sec; in 40,000 years, it should travel about 2.25 light-years. Your point stands, though. $\endgroup$ Sep 13, 2013 at 22:21
  • $\begingroup$ @PearsonArtPhoto: Reference: en.wikipedia.org/wiki/Voyager_1, first paragraph $\endgroup$ Sep 13, 2013 at 23:49
  • $\begingroup$ @KeithThompson: That's what I get for using the word speed, not velocity... $\endgroup$
    – PearsonArtPhoto
    Sep 14, 2013 at 0:16

1 Answer 1


No, as far as I can tell NASA got it right. Voyager 1 isn't going fast enough to reach AC +79 3888's current position in 40,000 years -- but the star is coming to meet it.

Assuming the current speed is 17 km/sec (as stated in the first paragraph of this Wikipedia article, and that it won't slow down much beyond that, it should cover approximately 1 light-year every 17,500 years.

AC +79 3888, also known as Gliese 445, is currently about 17.6 light-years away. But the star itself is rapidly approaching us, with a current radial velocity of -119 km/sec -- nearly 7 times as fast as Voyager 1's (Sun-relative) motion.

According to the above-cited Wikipedia article, in 40,000 years, Gliese 445 will be about 3.45 light-years away (but still too dim to see with the naked eye), and Voyager 1 will be 1.6 light-years from it.

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    $\begingroup$ That makes sense. Thanks! Guess it's not that NASA made a mistake, they are just making a big deal about something that's not that big of a deal (A mere 2/3rd of the way to the star...) $\endgroup$
    – PearsonArtPhoto
    Sep 14, 2013 at 1:01
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    $\begingroup$ @PearsonArtPhoto: I'd call it a moderately big deal. 1.6 light-years is pretty close; Voyager will be closer to Gliese 445 that it will be to the Sun. And Gliese 445 itself will be closer to us than the nearest star is now. (This all assumes nobody grabs Voyager and brings it back to the Smithsonian.) $\endgroup$ Sep 18, 2013 at 23:07
  • $\begingroup$ It's a little more complicated than just being 1.6 light years "short" of Gliese 445. In 40,000 years Voyager will be about 2.3 light years from Earth. If it was aimed directly at Gliese 445 it would be about 1.2 light years short of Gliese's at that time 3.45 ly distance. However Voyager is aimed to one side of Gliese so the closest encounter will be 1.6 light years. Another complication is that Gliese 445 is not really moving towards the Sun, it's essentially passing by it, with a closest distance of 3.34 light years that will occur about 6,000 years after Voyager's closest encounter with it $\endgroup$ Nov 14, 2023 at 12:09

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