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Stars move
Dec. 6th, 2010 06:09 pmHere are links to a couple of interesting discussions on James Nicoll’s LiveJournal. The first is a discussion of calculating the distances between real stars for purposes of writing an SF story, something I‘ve covered before. It includes this comment from Nicoll: “It's relatively uncommon these days for someone to put a planet around an actual named star and in a lot of cases it feels like the author just looked at a list of stars and grabbed ones that are listed as K > F. Age rarely comes into it and ditto metallicity.” Aargh. Oh, well, if I can keep one or two authors from inadvertently locating an Earthlike planet around a G star that’s only 50 million years old, or has already gone supergiant, I’ll consider the effort put into doing this DW journal well spent.
In the second essay, Nicoll reminds SF writers that stars move -- the ones we think of as “the closest” have not always been that way, and someday they’ll be distant stars again. In this same thread, SF novelist Charles Stross asks “… are there any online star maps showing models of how our neighbourhood (out to within, say, 40 light years) might look over, say, the next 5000 years?” He raises an important point: if your story takes place in the more distant future, it’s important to remember that the relative positions of the stars are going to change. For example, Wikipedia tells me that around the year 11,700, Barnard’s Star make its closest approach to Sol; it will be only 3.8 light years away at the time it starts to recede again. Around 28,700, Proxima Centauri will make its closest approach at 3.11 light years. And around 38,000, Ross 248 will come as close as 3.024 light years. And the other “nearby” stars will be approaching and then receding as well.
Unfortunately, I don’t know of any online star maps that fit Mr. Stross’s description. But if you’re going to write a far-future interstellar epic set tens of thousands of years from now, this set of web pages titled “The Armchair Astrometrist” is well worth a look. The meat, for our purposes, is on the page titled “Calculating Precise Long Term Stellar Motions,” but you should read through the preceding ones for full understanding.
Be warned: the calculations aren’t simple, but until some sort of program or online calculator is available, they’re going to be worth doing. To figure out where a star is going to be in a given future year (or where it was in a given past year), you’ll need the data on both its “proper motion” and “radial velocity” (see “The Armchair Astrometrist” for definitions). These are available in some star catalogues, and I‘ve also noticed that Wikipedia provides them for a lot of stars in our area. If I re-work these star profiles for a book or website, I think I will have to include these data for the use of authors who want to write far-future stories.
In the second essay, Nicoll reminds SF writers that stars move -- the ones we think of as “the closest” have not always been that way, and someday they’ll be distant stars again. In this same thread, SF novelist Charles Stross asks “… are there any online star maps showing models of how our neighbourhood (out to within, say, 40 light years) might look over, say, the next 5000 years?” He raises an important point: if your story takes place in the more distant future, it’s important to remember that the relative positions of the stars are going to change. For example, Wikipedia tells me that around the year 11,700, Barnard’s Star make its closest approach to Sol; it will be only 3.8 light years away at the time it starts to recede again. Around 28,700, Proxima Centauri will make its closest approach at 3.11 light years. And around 38,000, Ross 248 will come as close as 3.024 light years. And the other “nearby” stars will be approaching and then receding as well.
Unfortunately, I don’t know of any online star maps that fit Mr. Stross’s description. But if you’re going to write a far-future interstellar epic set tens of thousands of years from now, this set of web pages titled “The Armchair Astrometrist” is well worth a look. The meat, for our purposes, is on the page titled “Calculating Precise Long Term Stellar Motions,” but you should read through the preceding ones for full understanding.
Be warned: the calculations aren’t simple, but until some sort of program or online calculator is available, they’re going to be worth doing. To figure out where a star is going to be in a given future year (or where it was in a given past year), you’ll need the data on both its “proper motion” and “radial velocity” (see “The Armchair Astrometrist” for definitions). These are available in some star catalogues, and I‘ve also noticed that Wikipedia provides them for a lot of stars in our area. If I re-work these star profiles for a book or website, I think I will have to include these data for the use of authors who want to write far-future stories.