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!
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What I want to know is: what's the nearest star with a planet with life? Red dwarfs are common, but their habitable zone is close to the star and many of these stars put out powerful flares, like Proxima Centauri. The combination is not promising.
For more on the nearest stars, try this:
https://en.wikipedia.org/wiki/List_of_nearest_stars
You can see a nice rotating 3d map of them here:
https://upload.wikimedia.org/wikipedia/commons/c/c9/Stars-within-11-light-years2.webm
The map below shows 33 stars within 12.5 light years of us, made by Richard Powel.
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@johncarlosbaez I’m not in a rush to update Wells’ The Star!
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@johncarlosbaez
I imagine, in the cosmological sense, that this happens all the time.
It's almost inconceivable that passing stars don't regularly nudge normally far-flung object toward the inner planets, some of which presumably 'make contact' from time to time (?)
[#]cosmology #astronomy
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@johncarlosbaez in 30,000years they should rebrand Proxima Centauri as Lejana Centauri
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@johncarlosbaez is it reasonable to expect Voyager 1 will survive 45000 years?
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@jesusmargar - sure! It won't be running then, but it's incredibly unlikely that it will hit anything by that time.
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@johncarlosbaez I was thinking more of radiation than an actual crash.
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@johncarlosbaez Do those other stars, like Ross 248, have their own Oort Clouds? It looks like the two Oort clouds, if similar, could interact. I expect they are mostly empty space and unlikely to have actual collisions.
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@rlmcneary2 - that's a great question! I don't know which stars have Oort clouds. It could be that the best information about this presently comes, not from observation (since even our own Oort cloud is hard to see), but from simulations of solar system formation. I haven't read what these have to say about Oort clouds, but just intuitively I'd guess most stars with planets should also have an Oort cloud.
When two stars with Oort clouds come close, object in the Oort clouds won't hit each other much, but the gravity of each star will act to distort the other star's Oort cloud and send down a rain of comets.
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@johncarlosbaez Great post, John. Let me add the lists of the nearests exoplanets and galaxies: https://en.wikipedia.org/wiki/List_of_nearest_exoplanets and https://en.wikipedia.org/wiki/List_of_nearest_galaxies
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@riemannium - thanks!
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@johncarlosbaez I think it’s kind of funny that stars migrate and their planets are just along for the ride. Parents moving their kids to better spots.
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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 - the Arabs had cool star names: Kochab and Pherkad, for example! Brian Eno and Robert Fripp did an album The Equatorial Stars, with this track list:
Meissa" – 8:08
"Lyra" – 7:45
"Tarazed" – 5:03
"Lupus" – 5:09
"Ankaa" – 7:01
"Altair" – 5:11
"Terebellum" – 9:40
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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 @mattmcirvin @internic @dougmerritt
And here's Orion.
https://xkcd.com/3012/
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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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@mattmcirvin @johncarlosbaez @dougmerritt I saw (what I assumed was) Mars near the moon this morning, but I guess I am in the wrong hemisphere to see the occultation.
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@johncarlosbaez @mattmcirvin @internic @dougmerritt From the "Big Flyswatter" to "Big Scissor" (one half of a pair of scissors)
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@mattmcirvin @internic @dougmerritt @johncarlosbaez If that's so, why is it called the firmament?!?
(just kidding)
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@dougmerritt I'm probably somewhat more sensitized to this issue because I sometimes have to worry about converting between "inertial" coordinates (whose axes are fixed with respect to distant stars) and Earth-fixed coordinates (whose axes are fixed relative to the Earth's surface).
We like to think of the Earth as a rigid sphere that rotates along a fixed axis, but when you have to get a bit more precise it turns out it's none of those things; it's more of a wibbly-wobbly Earthy-worthy ball of stuff (to paraphrase Dr. Who).
(I put inertial in quotation marks because it often has the origin at the center of the Earth.)
@johncarlosbaez
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@internic - once upon a time I wrote a series of posts about the wobbling of the Earth:
https://math.ucr.edu/home/baez/wobble/
It was fun learning all that stuff. I should polish it up and put it on my blog!
@dougmerritt
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@johncarlosbaez @dougmerritt For a minute when I saw that they were a set of posts from sci.physics I wondered if I would recognizing them upon reading, but sadly no. I think that was after I stopped reading it as religiously.
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@johncarlosbaez @internic
Ted Bunn said in one of those sci.physics posts:
I'd guess that one possible answer is based on the wonderfully useful fact that everything in nature is linear, to first order.
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@dougmerritt - Yeah, that's hilarious and true. I forget who said it first - probably some famous physicist. I say it sometimes too!
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@johncarlosbaez I recommend ParallaxNick's "You Are Here: A Tourist's Guide to the Local Neighborhood" series.
https://www.youtube.com/playlist?list=PLa0TgREKn12hPWjg3hPWT91aEu30dNLfo
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@johncarlosbaez It would be nice to have an animated version showing the projected motions of the stars near the Sun, with Sun fixed at the center (i.e. "stationary"). It would be better having it in 3D view, which, alas, it is not yet up there (I am waiting for 3D holographic monitor screen to arrive, with attending computer technology to support that!). Oh well!
Also don't forget there may be a brown dwarf lurking near Sun. That one could play havoc with outer Oort cloud...we'll see!
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@thebluewizard - yes, it would be really great to have an animated 3d map of stars near the Sun.
If you have red-green glasses you can see a 3d map of nearby stars here:
https://en.wikipedia.org/wiki/List_of_nearest_stars#/media/File:Nearest_stars_rotating_red-green.gif
Alas, I don't have red-green glasses!
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@johncarlosbaez You can also play Elite: Dangerous which has a startlingly accurate map of the galaxy in it.
They had to make up most of the planets with an algorithm, but they did manually add a lot of the real exoplanets as they were discovered. Trappist-1 4 is a lovely Earthlike!
https://www.youtube.com/watch?v=6pPzNosr1Nk&t=410s
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@johncarlosbaez
Target Selection for SETI: 1. A Catalog of Nearby Habitable Stellar Systems (2002)
https://arxiv.org/abs/astro-ph/0210675
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@johncarlosbaez
The Target Selection for SETI catalog can be found here under HabCat
https://www.projectrho.com/public_html/starmaps/catalogues.php
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@nyrath @johncarlosbaez Tagging @setiinstitute , since Jill Tarter does not do social media.
However, that list does not include all of the M-dwarf nominal-habitable-zone planets that we now know are common.
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@michael_w_busch @nyrath @johncarlosbaez @setiinstitute Any update on the Trappist planets? Last I heard they were surprisingly airless.
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@hendric @nyrath @johncarlosbaez
The most recent results I am aware of for TRAPPIST 1-b are consistent with either bare rock or a Venus-like thick CO2 atmosphere: https://arxiv.org/abs/2412.11627 .
But the other planets are further out and cooler.
More data is pending.
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@johncarlosbaez Why did I never hear of Groombridge 34?
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@johncarlosbaez I made a list of stars with xyz coordinates https://www.drivethrurpg.com/en/product/369748/solis-people-of-the-sun-alpha
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@johncarlosbaez
Strongly evokes a half-remembered illustration in one of Larry Niven's "Known Space" novels.
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@johncarlosbaez
I wonder when a star will get really close to the Sun, like 1 or 2 light years?
Gliese 710 is heading almost directly towards the Sun and will pass about 1/6 light year from the Sun in about 1.29 million years. The Hipparcos mission got accurate enough data to show Gl 710 will get close, but Gaia refined the figures significantly in the last few years.
Spectral type K7 V, so not a red dwarf, but also well below solar luminosity. Still more than massive enough to do…umm, fun things to the Oort Cloud.
https://en.m.wikipedia.org/wiki/Gliese_710
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@dpnash - wow! I'm going to add that event to my calendar:
https://math.ucr.edu/home/baez/timeline.html#future
Any word on whether planetary orbits will be noticeably disrupted? Sometimes small changes in orbits can have bigger long-term effects.
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@johncarlosbaez Good question. I don’t know enough celestial mechanics to have a good sense. The associated Wikipedia article states that the close pass will definitely disrupt the outer Oort Cloud but likely have “negligible” effects on Pluto+Charon, and so even more negligible effects on the inner solar system.
The Wikipedia page for the nearest stars mentions a few other close passes, both past and future, but nothing as close as Gliese 710, and (unsurprisingly) most of the close passes are by significantly smaller objects. https://en.m.wikipedia.org/wiki/List_of_nearest_stars
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@johncarlosbaez My reaction to this was "wait a minute, since when were 'Rigil Kentaurus' and 'Toliman' specifically the names of α Cen A and B , rather than just being two different old names for the A/B pair?"
Turns out the answer is: since 2016 and 2018 respectively, by somewhat arbitrary decision of the IAU, since they decided to start blessing proper star names. It's elegant, though perhaps not ratified by history.
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@mattmcirvin - heh, I didn't even think about how the old astronomers couldn't resolve α Centaurus A and B into two separate stars! But I like these names.
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@johncarlosbaez I recall an old kid's book on astronomy that described Alpha Centauri as "actually three stars close together", but from a visual perspective that's not quite right: Proxima's orbit is so huge that if it were bright enough to see with the naked eye, it wouldn't even look like part of a multiple star system; it'd just be another star in Centaurus. We can't resolve it easily because it's dim.
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@mattmcirvin @johncarlosbaez : This makes me wonder how it would have affected the history of autonomy if it were visible with the naked eye. Like Galileo seeing the moons of Jupiter, except going back to the dawn of history (and involving a non-wandering ‘fixed’ star).
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@mattmcirvin @johncarlosbaez Even more specifically, the IAU gives a maximum of one star in a system a specific proper name—which is why they had to use 2 traditional names for Alpha Centauri to name the two bright components.
This rapidly gets awkward when trying to draw and label a star chart when you’ve got a multiple star system and only one component is assigned a traditional name by the IAU.
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@dpnash @mattmcirvin - more people would pay attention to this if they realized that when you officially name a star, you can will it to your children, so your descendants will own the rights to it when we colonize its solar system.
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@johncarlosbaez @dpnash so we can combine the "star registry" scam with the nearly identical "Established Titles" scam--call me the Laird of HD 203291...
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