We may think of the stars in the sky as fixed, but if we wait the closest stars will eventually drift away - and other stars will come closer. This graph shows how that works. The vertical blue line is today.
Today the nearest star is Proxima Centauri, just 4¼ light years away. It's a small red dwarf with 2 or 3 planets. Unfortunately it shoots out big X-ray flares. It orbits two other stars: one, called Rigil Kentaurus, is a bit bigger than the Sun, while the other, Toliman, is a bit smaller. They orbit each other every 79 years, while Proxima Centauri orbits both of them every 500,000 years.
But if we wait, various other stars will drift by and temporarily become closer!
Barnard's Star will swing by and tie Proxima Centauri for a short time 10,000 years from now. It's just a bit bigger than Proxima Centauri, and it has one planet.
Ross 248 will be the closest star for about nine millennia starting 30,000 years from now. It's another red dwarf, with huge starspots due to its powerful magnetic field.
Then Gliese 445, yet another red dwarf, will become the closest star for a while. During this time the Voyager 1 probe will pass within 1.6 light years of this star.
And so it goes. I wonder when a star will get really close to the Sun, like 1 or 2 light years? This could shake up the Oort cloud, the cloud of icy bodies in our solar system that stretches out for 1.5 years. Then we'd get lots of comets!
(1/2)
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@johncarlosbaez
We may think of the stars in the sky as fixed
And for example, and rather dramatically, just a couple millennia ago Polaris was not the pole star:
"From around 1700 BC until just after 300 AD, Kochab (Beta Ursae Minoris) and Pherkad (Gamma Ursae Minoris) were twin northern pole stars, though neither was as close to the pole as Polaris is now."
https://en.wikipedia.org/wiki/Pole_star
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@dougmerritt @johncarlosbaez But I believe the change in which is the "north star" has less to do with the relative motion of stars and more to do with the changing orientation of the Earth (precession of the equinoxes).
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@internic @dougmerritt - good point! And now that I think about it, those stars are too far away to easily detect their actual motion.
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@internic
Yes indeed; thanks. I had a feeling I was forgetting something important.
It is nonetheless interesting that the stars are, for multiple reasons, less eternally fixed in position than it intuitively seems.
@johncarlosbaez
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@dougmerritt @johncarlosbaez Agreed! Another interesting thing to think about is how constellations will change over time, since, for the most part, they're just apparent patterns of stars that are not gravitationally bound to one another (or even necessarily that close together). Of course, since they're mostly more distant, I think it will generally take a long time for them to change significantly.
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@internic @dougmerritt @johncarlosbaez This is a particular bugbear of the science-fiction critic James Nicoll--turns out there are a lot of science-fiction novels that blithely assume that Alpha Centauri is still the closest star to Earth millions or billions of years in the past or future. "STARS MOVE" is one of his go-to phrases.
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@mattmcirvin @internic @dougmerritt - here's the past and future of the Big Dipper from 100,000 years in the past to 100,000 years in the future.
https://www.popularmechanics.com/space/deep-space/a20347/how-the-big-dipper-has-changedand-will-changeover-200000-years/
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@johncarlosbaez @internic @dougmerritt notice that 5 of those stars seem to be moving together-- that's the Ursa Major Moving Group, a collection of stars that may have once been a bound cluster. That's the core of it, which is about 80 light years from here, but there's a wider collection of stars apparently associated with it that are all over the sky, because we and the Sun are passing through it, though not of it.
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@johncarlosbaez @internic @dougmerritt Astronomers once believed that Sirius was part of the Ursa Major Moving Group, but it's too young to be physically associated with the rest of them. Menkalinan (Beta Aurigae) and Alphecca (Alpha Coronae Borealis) are in it though.
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@johncarlosbaez @internic @dougmerritt It used to be called the Ursa Major Moving Cluster, which you can sing to the Teenage Mutant Ninja Turtles song
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@mattmcirvin @internic @dougmerritt - nice! You know a lot about stars, Matt.
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@johncarlosbaez @internic @dougmerritt mostly I have fragmentary memories that I can supplement with Google and Wikipedia. But while I'm not a very energetic amateur astronomer in the sense of having telescopes and such, I was always really into it as a kid so I absorbed a lot of lore then.
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@johncarlosbaez @internic @dougmerritt there is a lunar occultation of Mars going on right now, btw, I'd completely forgotten about it
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@mattmcirvin - I think I just missed it! I went out in the dark to pick some fruit (don't ask), and I saw Mars very close to the Moon. I think it's farther now!
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@johncarlosbaez well, I posted a terrible phonecam picture for everyone
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@mattmcirvin - it was terrible, but charming, like the first blurry photo of some exotic phenomenon.
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