This web page is somewhat of a white paper discussing the astronomical possibilities of life-bearing planets within the 'immediate' stellar neighborhood; that is, within roughly 50 LY (light years) of Sol. The general audience I envision is fans of science fiction, most particularly hard science fiction, though beginning writers (like me) may find this page useful. For those with a background in astronomy, this may be a refresher course.
Primarily, these pages grew out of my own research into a story I wrote about a human colony around another star. I thought I would just pick some well-known star the appropriate distance from Sol from a star chart (the story required a distance of 40 LY, but it wasn't too picky about local conditions other than local plants and fish). It turns out that named stars tend not to be good places for life, or colonies. Named stars have names because they are quite visible in our sky, but in terms of a scientific possibilities for life-supporting planets they turn out to be too young (Vega), too old (Betelgeuse), too big (Capella), too small (Barnard's), too far (Rigel), too hot (Sirius), too cold (Wolf 359), or too many (Castor). My research into local stellar environments, coupled with my lifelong interest in astronomy, made me decide to write an article about what it takes for a star to be capable of hosting life supporting planets, consolidating the research of many that have gone before me (see Bibliography).
For the purposes of life, I am assuming Earth type life, that is organic (carbon based) requiring a lot of water and oxygen. We may speculate about exotic life such as silicon based, but it is harder to predict what the best environment would be as we have yet to run across any examples of it among perhaps 20-100 million species of life on Earth. Earth life has proven to be extraordinarily resilient, from life in 600 degree volcanic water to bacteria accidently sent to the moon on a Surveyor probe and proved alive years later after their return by Apollo astronauts. Because of this, I feel it is not too far-fetched to assume that carbon/water life will take hold given the proper environment. Be aware that this is an extremely debatable subject. However, in science fiction we try to exploit the possible and aren't necessarily trying to win Nobel prizes in exobiology.
The scientific plausability of all of this is further debatable. Many astronomers (or biologists for that matter) refuse to go too far out on a limb to suggest which stars look promising because this science is so far in its infancy, you might as well call it pre-fetal. However, there are quite a lot of theories to suggest which types of stars would be incapable of hosting life, or at least would make it extremely unlikely. Therefore, it is up to the author to decide how far to push current theories to support a story around a particular star. I try to remember the classic editor's rejection of far-fetched science: 'Suspension of disbelief does not mean hanging it by the neck until dead'.
There are three main areas of astronomy that can help narrow down the possibilities of finding a likely star. The first and biggest help, though the most complicated, is the 'Spectral Class' of the star and it's associated trivia. The second is the star's age and lifespan, and the third is the multiple star characteristics of the system.
The Hertzsprung Russell Diagram
The Hertzsprung Russell Diagram is probably familiar to anyone who has taken an astonomy class, or has ever picked up a generic book about astronomy. Here's a version from Jim Smith's Free Virtual Galaxy Project, I'm sure you've seen a similar one:
Here's a quick review. The brighter a star is (usually from an arbitrary distance of 32.6 LY -- 10 parsecs), the higher it is on the chart. Dimmer is near the bottom. The horizontal aspect of the chart is temperature -- hotter stars to the left, cooler stars to the right. Your Astronomy 101 class probably pointed out where the sun lies (and almost all H-R diagrams have a big yellow dot in the middle of the main sequence saying 'We Are Here', just like this diagram does). You were probably taught the spectral classes of stars, O B A F G K M, and probably several mnemonics to help you remember them, from 'Oh Be A Fine Girl Kiss Me' to the classic rebuttal 'Only Boys Accepting Feminism Get Kissed Meaningfully'. Spectral classes are further subdivided into numbers, 0 is warmer than 9, and Sol turns out to be a G2 star. O stars are usually hot/bright, and M stars are usually cool/dim, with exceptions such as white dwarfs like Sirius B (hot, dim) and red supergiants like Betelguese (cool, bright). You were probably also taught, usually with a strange smugness, that our star is a yellow dwarf star with no distinguishing characteristics to make it seem special in any particular way.
It's all coming back, right? There are a few things on this chart that make things interesting for planet hunting, and almost all of it revolves (so to speak) around the mass of the star. Mass is not explicitly plotted on the H-R diagram, but it generally corresponds with the temperature of the star -- all the stars on the main sequence to the left of Sol tend to have more mass and stars to the right tend to have less mass. This is less evident off the main sequence, or at least it doesn't translate directly. For instance, white dwarfs tend to be at the lower left in the OBA areas, but generally have masses near that of Sol, while some red giants (not supergiants) may also be near Sol's mass, though they fall to the right and above.
Because mass doesn't disappear, stars don't generally drift through the main sequence. After the first few percent of a star's age (less than 5 percent), the star generally stablizes and stays at the same general spot on the H-R diagram for up to 90 percent of it's life. Even at the end of Sol's life, when it expands off the main sequence to a red giant, it may still technically be a G (or perhaps low-K) class star based on its temperature, luminosity, and mass. Some variable stars shift slightly, however, and there is a theory that the ice ages may have been caused by small 'wiggles' in solar luminosity (though after seeing the effects of the last El Nino cycle, I tend to agree with the theory that the ice ages were caused by the rising Himalayas shifting the jet stream).
For purposes of likely life sustaining planetary systems, we probably don't want to look too far below the K class stars. At that point, we're looking at a typical mass of half that of Sol's (with 0.2 times the luminosity of Sol), and the M class stars run around a quarter of Sol's mass (with 0.005 times Sol's luminosity). When stars head towards the basement of K class, any warm planets would have to snuggle closer to its host star to stay where water has a good chance at remaining a liquid. This runs the risk of tidally locking the planet so that one face stays towards its star -- which can cause undesirable weather and temperature problems. Additionally, many stars flare, which causes a greater risk of deadly radiation regularly sterilizing close planets.
On the other end of the scale, we probably don't want to look above F class stars. O through A stars have high levels of ultraviolet radiation and tend to have high stellar winds which could strip away an atmosphere. OBA stars tend to rotate rapidly as well, and there are theories that rapidly rotating stars don't generate many planets (or perhaps it's the other way around and OBA stars rapidly rotate because they don't have many planets to slow the stellar rotation).
This implies likely candidates in the F, G, and K classes, with G perhaps as optimum merely through being the center of the range. As it turns out, there are many more stars of low mass than stars with higher mass. For every 100 stars, statistically there are 67 M class stars, 13 K class, 7 G class, 3 F class, and maybe 1 A class (and probably none of the rare O and B class stars). Out of 400 billion stars in the galaxy, this gives us roughly 90 billion FGK candidates, less than twenty-five percent, with seven percent being G type (26 billion).
Spectral classes can be further subdivided by a roman numeral based on size (related to luminosity) called the Yerkes scheme:
Ia Luminous Supergiants Ib Less Luminous Supergiants II Luminous Giants III Normal Giants IV Subgiants V Dwarfs VI Subdwarfs
Generally class V stars are called dwarfs because they are much smaller than classes Iab through IV. However, the term 'dwarf' is statistically a misnomer -- 90 % of stars fall in the main sequence V class and are class F and cooler. Due to problems of tidal locks and flares, we want the V class stars (though we can, perhaps, get away with a small IV class member under ideal conditions). The star Canopus (in the constellation Argo) provides a good example for checking the Yerkes class; Canopus is a 'F0II' star. F0 is perhaps a little toasty for life, but still yellow-white and on the borderline of our acceptable FGK selection. The II, however, labels it as a luminous giant and in fact its diameter is 65 times that of Sol, with a violent corona emitting strong X-rays and radio waves.
There is one more set of miscellaneous data usually prefixed or appended to spectral class:
D Degenerate. A white dwarf, as in Sirius B, type DA2 d usually a red dwarf, as in Proxima Centauri, type dM5e. Yerkes
class V is more modern.
sd subdwarf (Yerkes VI these days)
e strong emissions (indicate a large, thick hot gas cloud or corona surrounding the star) m abnormally abundant heavy elements (usually metals, sometimes non-hydrogen/helium) n nebulous absorption lines (usually due to high stellar rotation) neb nebula spectrum mixed with the star p other peculiar feature (usually abundance of an unexpected element) var variable star wl weak lines (usually old, metal-poor stars)
If one looks at stellar potentials, such as Canopus, Sol may seem like an uninteresting, dim, small, yellow dwarf. However, since spectral class is linked to mass, Sol actually has more mass than the average star. As there are more K and M stars than any other, Sol's G2 status actually makes it brighter than most stars. Given the actual statistics, Sol is actually brighter, bigger, warmer, and rarer than most of the stars in the galaxy.
If we use Earth evolution as a guide, it took roughly 3 billion years for evolution to get out of the single-cell stage once life evolved. It took that long to 'terraform' the atmosphere into one that provided free oxygen, and thus give the potential for more active, multicellular life. It took 540 million years from the 'Cambrian Explosion' of multicelled evolution to Homo sapiens. There were a lot of false starts in this due to great extinctions, some of them extra-terrestrial catastrophies (such as the possible Yucatan impact at the end of the Cretaceous), some were terrestrial in origin (the trilobite extinction may have been caused by planetary weather changes due to mass vulcanism in what is now Siberia). Many other events, from sunspot cycles to continental drift, have affected the evolution of our modestly intelligent species. Perhaps these events were necessary to weed out life that may have restricted or competed with evolved intelligence. Perhaps if the Yucatan impact had not occurred, an intelligent, warm-blooded dinosaur would have evolved 50 million years earlier than intelligent mammals.
In any case, based on Earth, we can estimate roughly 500 million years of multi-cellular evolution to get to humans, plus 3 billion years of single-celled life, plus 500 million to 1 billion years for the Earth to absorb solar system debris and to cool down from formation. We can speculate on variables: Perhaps a star formed from a high oxygen/water nebula could cut out a billion years or two of single-celled terraforming. Perhaps evolution is quicker and more competitive on a planet that's surface is one-third water instead of three-quarters. Unfortunately for the biologist, these guesses are purely theoretical. Fortunately for the science fiction writer, unproven theories don't always hinder story development. From planet formation to intelligent life, call it maybe 3 billion years on the low end, maybe 6 billion on the high end. Non-intelligent prolific life may occur in a shorter period of time, but remember that Earth life was mostly slime, bacteria, and algae until the Cambrian.
Mass affects the density of the star, which affects the fusion rate of the star, which in turn affects the potential age of the star. An A0 star like Vega will probably only live for a billion years. An M4 star like Barnard's may live for 50 billion. A giant O star's life is miniscule; Alnitak (the first star on the left of Orion's belt) is around 6 million years old and has already run out of hydrogen. During the lifetime of Alnitak, humanity has evolved from just before Australopithecus afarensis (Lucy) to Homo sapiens. Alnitak probably wasn't more than a lump in a nebula in the dinosaur era.
The lifetime of a star again limits us to our FGK spectral class for potential evolved life, though it's not out of the question for a non-FGK star to host a potential colony. Science fiction fans of Larry Niven may note that Jinx is a habitable colony around Sirius A. Sirius A is an A1V class star, twice the mass of Sol, doomed to a short lifetime of maybe a billion and a half years, and probably pumping out enough UV radiation to fry any life on a nearby planet. However, Niven's stories establish that Jinx is actually a moon around a gas giant primary. Although it is not mentioned in his stories, the primary may be far enough away from Sirius A so that the UV radiation is low. Gas giants tend to be heat providers; Jinx may be in a water-temperate zone outside of the normal liquid-water range of Sirius A. Furthermore, the local species on Jinx, mainly Bandersnatch, have been established as being genetically engineered lifeforms planted there by another race (Bandersnatch are even immune to genetic radiation damage due to large chromosomes). I don't know how much of this was known when Niven wrote his first Jinx story, but his scenario is possible theoretically.
Which brings us to the question of a star's actual age. How old is Sirius A? If its 100 million years old, then planets probably haven't finished forming (if they're there at all) and the star wouldn't have even started fusing yet when the Slavers were moving Bandersnatch around. On the other hand, if Sirius A is fairly mature, say 1.2 billion years old, things look more possible.
Unfortunately for the astronomer (and also for us, in this case), we really don't have a good way of figuring out the actual age of an individual star (there are exceptions, especially in the case of Sirius). We know that Sol is about 5 billion years old because that's how old the rocks are on Earth and the Moon (and, lately, Mars). There are theories currently being tested: One is that sunspot cycles decline as a star ages. Another theory is trying to determine how much hydrogen has fused from the interior of a star; like Carbon-14 or Uranium testing, this may tell us how long a star has been on the main sequence by calculating the ratio of helium to hydrogen. However, there is no reliable way currently being used to age a star, with the exception of very young stars (like the Pliedes members, which are still in their birth nebulae) or very old stars (like Betelgeuse, which is currently fusing heavy elements, having run out of Hydrogen and Helium).
Multiple Star Systems
The final stellar obstacle to work around is the large presence of multiple stars. In the closest 100 stars to Sol, 23 are members of binary or multiple star systems. Orbital dynamics of planets in these multiple star systems may be tricky for many reasons.
Close multiples may just not have any room for planets. Take Castor, for instance, one of the 'Twin' stars of Gemini and appearing to the naked eye like a bright, hot class A star. When examined closely, Castor looks like three stars -- a pair with a 400 year orbit, surrounded by a faint companion 1000 AU from the inner pair. Spectroscopic analysis actually shows that Castor A is a two star binary orbiting each other in an ellipse about the size of Mercury's orbit, revolving once every 9.2 days. Castor B is also a binary, with closer stars making an orbit every 2.9 days. The faint companion star is also a binary, two M stars that are so close they nearly touch and orbit each other every 20 hours. Castor turns out to be a six star system, one in which planets would probably not last long enough to even finish forming, let alone develop life.
A planet probably cannot hold a orbit around two stars at once; that is an ellipse or circle with two stars within the orbit. The stars orbiting each other just cause too many orbital pertubations for a stable orbit, unless the orbit is tremendously huge and the two center stars extremely close. Figure eight orbits, or other complex round-robin orbits, also probably wouldn't last more than a few thousand years in a realistic environment (a figure eight might be temporarily stable with two stars of identical mass, far apart, and slowly revolving. However, the odds of such a stellar system are bad enough without throwing in a renegade planet).
Far binaries tend to be better from an orbital dynamic point of view. Take Alpha Centauri, our nearest neighbor. This system is actually three stars. Proxima Centauri (Alpha Centauri C) is a dM5e red dwarf over 13 thousand AU from Alpha Centauri A and B, making an orbit once every few hundred thousand years. Due to this distance, Proxima would most likely not interfere with the orbital dynamics of any close-in planets. Alpha Centauri A and B turn out not to be that close, either. They orbit each other with a period of around 80 years in a wide ellipse, coming as close as 11 AU (just past the orbit of Saturn), then receeding to 35 AU (just past Neptune). It turns out that orbits of planets under 3 AU per star may be stable. Since Alpha Centauri A is a G2V (virtually a twin of Sol), and Alpha Centauri B is a cooler K0V, this makes it possible for a stable planet in the liquid-water zone around each star! Imagine how quickly space travel might develop in a system with two habitable planets no farther apart than half our own solar system.
Unfortunately, things may not be so rosy in such a system. In our system, the Kuiper belt of asteroids and dust starts just past Pluto (or, perhaps Pluto and Charon are the biggest Kuiper objects, in which case the belt starts just past Neptune). There is also the Oort cloud of comets starting at around 10 thousand AU from Sol, extending perhaps all the way out to 100 thousand AU. If the Centauri system were similar to ours, Alpha Centauri A and B would start drifting near their Kuiper belt every 80 years and Proxima would be sweeping through the suburbs of the Centauri Oort cloud. The number of comets and asteroids buzzing through that system must be enormous, and may regularly impact any planets (would this make life more likely or less?). Or, perhaps the system may have been swept clean pretty early in its lifetime, though there seems to be evidence that Proxima Centauri has a super-Jovian companion planet due to orbital wobbles.
What the Neighborhood Looks Like
Using this data, which nearest stars might support life, if not actually generate it? Let's hit the closest 25 stars, in order, heading away from Sol.
Personally, I lean against the Centauri system for intelligent life, though I like it for multicellular if it's old enough. It would be a great place to get our feet wet with a colony or two. I would guess that the Centauri system might have too many asteroid and comet impacts to generate any lasting civilization (though this is just my gut instinct and probably wouldn't stop me from writing a story about it). The views, however, would be spectacular -- two suns and maybe yearly or monthly comets.
The next two stars, Barnard's (M5V) and Wolf 359 (the M6 system of Star Trek Federation vs. Borg fame) are M type reds, which I tend not to like for life of any kind.
Gliese 411, also known as UV Ceti, (M2Ve, probably a double) seems a close borderline to K, but it has this unfortunate habit of flaring more than several times it's brightness in a matter of seconds.
Next is Gliese 65, which are two identical 'dM5.5e' red dwarfs that would only warm the heart of an astrophysicist.
Sirius is next, probably too young for life and it's too hot anyway. If life had made a start, I would guess that the entire system had been sterilized when Sirius B collapsed.
Two more red dwarfs follow, Gliese 729 (dM4.5e) and Ross 248 (dM6e). A whole lotta nothing with either of them.
Epsilon Eridani (K2V, about 10.7 LY out) is one of those interesting borderline stars. It's a cool star, and one that flames a lot, so things don't generally look good for the gonads. However, there is evidence in the star's wobble that it has at least one large planet around it, and infrared tests have found a dust ring. Epsilon Eridani may be a young star just in the beginning stages of forming planets. If the flares calm down, this may be a spot to watch (in a billion years or so). However, if I had a choice on whether or not to send a probe here, I'd roll the dice and send one out.
Next in line are Ross 128 (dM4.5), Gliese 866 (a possible double M5e), and GX Andromeda (a double, M2V and M6Ve). All cool reds, probably fairly sterile.
Epsilon Indus is next, a K5Ve (possibly a mildly warmer K4Ve) about 11.3 LY out. I couldn't find much information either way about this star. It's a little chilly, but it might be older and a better candidate than Epsilon Eridani.
61 Cygni is a double K class (K5Ve and K7Ve) also 11.3 LY away. They are far apart enough (a mean of 84 AU with a 653 year orbit) that either might have several planets. 61 Cygni A might be a flaring variable, and that's the warmer one of the pair. 61 Cygni B might be inviting, however, and they're close enough that it might be close enough to try a two-for-one.
After 61 Cygni is Gliese 71, a double red dwarf (dM4 and dM5) of no obvious interest.
We may hit the jackpot with Tau Ceti, a G8Vp star 11.4 LY away. This star is slightly cooler than Sol, but still a G type star. Unlike Alpha Centauri A, Tau Ceti isn't a member of a multiple. If Tau Ceti is old enough, this is probably the best place in the nearest 50 stars to look for life or find a nice, comfortable planet to settle on.
Procyon is the last out of the 25 nearest stars and it appears to be a cooler cousin of Sirius. At F5IV-V, it's warm and big, but in our range of likely stars. Procyon, like Sirius, has a white dwarf companion star with an orbit of almost 41 years. The mean distance of the stars is 14 AU, however, which is fairly close -- any planets might have to be fairly close to Procyon A, which may make them too hot for life.
One of the nice things about the web is that it is easier to create 'living' documents that may change as time goes on. In this section, I'll add links to new theories about planet formation or life that might fit in with the theme of this document.
Here Come the Suns -- (added 19 Mar 00) Scientific American article. We've found almost two dozen planets orbiting other stars by now, and the similarities between the stars they orbit are interesting: The stars tend to be metal rich (metals or heavy elements, to an astronomer, is any element other than H or He). Note Tau Ceti above -- as a G8Vp, the 'p' stands for a peculiarly large amount of an element (Calcium, if I remember my research). Does this make Tau Ceti an even more likely candidate for planets? A corollary -- metal rich stars tend to be near the core of the galaxy. A metal rich star has to be formed from the supernova remnants of an earlier, dead, star. The optimum distance might mean out a ways from the galactic core (high metals, but also a lot of bombarding junk and frequent supernovae), yet not too far out (where there aren't many older stellar graveyards). Like the 'water zone' of the solar system, a zone where life is likely due to the probability of liquid water, the galaxy may have a 'planet zone' of stars where the amount of metals in the nebulae stars are formed from reaches optimum. This 'planet zone' may be fairly narrow, and the Sun may be right in the center of it.
Stellar Database -- (added 19 Mar 00) Stellar database. Alpha Centauri has 150% the metal content of Sol, which may be a good sign for planet formation. It's age may also be 4.2 billion years, which would be good for multicellular life. In Earth evolution, 4.2 billion years might range from the Cambrian Explosion to around the time of the first land animals (bugs, mostly, like millipedes), but before trees and even ferns -- plant life on land is waxy algae. Neat database -- has a lot of information for close stars, and annotations as to where the information comes from.
Chromospheric Age Dependence -- (added 19 Mar 00) Astrophysical Journal article. Some serious Hard Science: How does one measure the age of a star? This is a Journal publication of a procedure tested by Don C. Barry of USC. It is a dense academic article, you've been warned. The theory is that stars slow down their rotations as they age, and eject more mass into their solar wind. Errors in age can sometimes be up to 20% for mid-life stars, but it might give a good ballpark estimate. The paper calculates the ages of the 115 F and G Dwarf stars in known clusters, though the catalog it uses to name the stars seems to escape me (all stars are refered to by a number that isn't the Gleise number or any other catalog I recognize -- it may be the Woolley catalog). Interesting tidbit: In the observed stars, there was a burst of star formation ending around 4 billion years ago, and another burst beginning 400 million years ago. Oddly, there aren't many stars in this group that are between 0.5 billion and 4 billion years old.
3-D Starmaps An utterly cool set of pages containing star databases and pictures of the local stellar neighborhood. Some maps are in 3-D if you have those funky red-blue 3-D glasses. You can get the unedited Gliese catalog here, which is a database of the closest several thousand stars and their spectral types.
Bibliography (for the main paper)
Stars Gives a history of one star per week, usually mentioning size, class, and other interesting trivia.
Stars of the Milky Way A page about spectral types of stars.
The Zeta Reticuli Incident Okay, on the surface, this starts as a discussion about Betty and Barney Hill (you remember, they claim they got abducted by grey aliens back in the 60's) and explores the possibility that the abducting Greys come from Zeta Reticuli based on a star chart Betty Hill dragged out of her mind during hypnosis. The page quickly degenerates into the reprint of the Astronomy Magazine flame war between Carl Sagan and Steven Soter vs. a host of others who tried to be more 'open minded' about the incident. (IMHO, both sides are fairly rigid blinder-wearing extremists). In the flotsam, however, are interesting theories about what it takes for stars to contain planets, and the possibilities of planets in multiple star systems. It also demonstrates how much in its infancy this 'science' is.
The Classification of Stellar Spectra A page that discusses the lesser-known aspects of spectral types, especially stars that don't quite fit the H-R diagram.
Hertzsprung-Russell Diagram University of Oregon Atronomy department class notes about H-R and spectral types.
Astronomy103:H-R Diagram Ditto, but this is George Mason University's.
Planets around Binary Stars A NASA 'Ask the Scientist' question and answer about planets around multiple stars.
Centaurus A discussion of the constellation Centaurus and stars within. Interesting info about Alpha Centauri.
Spectroscopic Binary Catalogue If you want to get down-and-dirty in the details about the known binary/multiple stars (such as orbital period, semi-major axes, etc...), then this is the database for you.
Hipparcos FAQ Hipparcos was a probe the Europeans sent out into the middle of the solar system to look at stars. Like the Gliese catalogue, it came back with a database of thousands of stars with probable distances and spectral classes. Unlike the Gliese catalogue, it limited itself to stars above a certain magnitude. This means it possibly missed very close, but dim stars.
Hipparcos Closest Stars Here's a list of the closest stars in the Hiparcos Catalogue. You can see it missed some I used in the essay above -- that's because I used the Gliese catalogue, which includes dim stars.
Alpha Centauri More Alpha Centauri data, supplied by SciFi writer Robert J. Sawyer.
Nearby Stars Another list of the closest stars. I think this one is Gliese based.
Free Virtual Galaxy Project More H-R discussion, and I stole the H-R GIF from this site.
Scientific American's Ask the Expert A page about how to tell how old a star is.
Sky & Telescope's Spectral Classes Further discussion about H-R and spectral classes.
Vulcan's Sun Okay, this is indeed a discussion about which star Spock is from, but it's from Sky & Telescope and it discusses the possibility of planets around multiple star systems.
Nearby Stars This is actually part of a group of pages about Biblical interpretation, but it mentions an interesting puzzle about Sirius being described 2000 years ago as a red star.
White Dwarfs A discussion about the end-life of Main-sequence stars, from Ohio State University
The Dogon and Sirius From the Skeptic's Dictionary, a discussion about the Dogon tribe of Africa and Sirius.
Extra-Solar Planets The Darwin Mission's list of planets discovered around nearby stars (usually either dust rings, like Vega, or super-jovians like Bernards).
(Update 20 March 2000 -- fixed some things pointed out to me concerning dwarf and subdwarf designations.)
(Update 19 March 2000 -- fixed some broken links, a mis-label of Canopus, changed some wording that bugged me, added theory section)
Back to Essays
Back to Science Fiction

Is páipéar bán é an leathanach gréasáin seo a phléann na féidearthachtaí réalteolaíocha a bhaineann le pláinéid ina bhfuil saol laistigh den chomharsanacht réalta 'dlí'; is é sin, laistigh de thart ar 50 LY (bhliana solais) den Sol. Is lucht leanúna ficsean eolaíochta, ficsean eolaíochta crua go háirithe, is iad an lucht féachana ginearálta a shamhlaím, cé go bhféadfadh scríbhneoirí nua-aimseartha (cosúil liomsa) an leathanach seo a fháil úsáideach. I gcás daoine a bhfuil cúlra acu san réalteolaíocht, d'fhéadfadh sé seo a bheith ina chúrsa athnuachana.
Go príomha, d'fhás na leathanaigh seo amach as mo thaighde féin ar scéal a scríobh mé faoi choilíneacht daonna timpeall réalta eile. Shíl mé go roghnódh mé réalta maith ar bith an fad cuí ó Sol ó chairt réalta (riachtanaigh an scéal fad 40 LY, ach ní raibh sé ró-chasta faoi choinníollacha áitiúla seachas plandaí agus iasc áitiúla). Tá sé ag teacht amach nach bhfuil réaltaí ainmnithe ina háiteanna maithe do shaol, nó do choilíneachtaí. Tá ainmneacha ag réaltaí ainmnithe toisc go bhfuil siad le feiceáil go leor inár spéir, ach ó thaobh na féidearthachtaí eolaíochta do phláinéid a thacaíonn le saol, bíonn siad ró-óg (Vega), ró-shean (Betelgeuse), ró-mhór (Capella), ró-bheag (Barnard's), ró-fhada (Rigel), ró-te (Sirius), ró-fhuar (Wolf 359), nó ró-iomarca (Castor). Chuir mo thaighde ar thimpeallachtaí réalta áitiúla, mar aon le mo spéis ar feadh an tsaoil i réalteolaíocht, orm cinneadh a dhéanamh alt a scríobh faoi na rudaí a theastaíonn le haghaidh réalta a bheith in ann pláinéid a thacaíonn le beatha a óstáil, ag daingniú taighde go leor a chuaigh romham (féach Leabharlann).
Chun críocha na beatha, táim ag glacadh le saol cineál na Talún, is é sin orgánach (bhunaithe ar charbóin) a éilíonn go leor uisce agus ocsaigin. D'fhéadfadh go mbeimid ag smaoineamh faoi shaol coimhthíoch mar a bheadh bunaithe ar shilíciam, ach tá sé níos deacra a thuar cad é an timpeallacht is fearr a bheadh mar nach bhfuil muid fós ag rith ar aon samplaí de i measc b'fhéidir 20-100 milliún speiceas saoil ar an Domhan. Tá sé cruthaithe go bhfuil saol na Talún thar a bheith athléimneach, ó shaol i uisce bolcánach 600 céim go baictéir a cuireadh go mícheart chuig an ghealach ar fís-scrúdaitheoir agus a bhí beo blianta ina dhiaidh sin tar éis a n-aisghabháil ag spásairí Apollo. Mar gheall air seo, ní dóigh liom go bhfuil sé ró-fhada a glacadh leis go mbeidh saol carbóin / uisce a ghlacadh a chur i bhfeidhm a thabhairt ar an timpeallacht cuí. Bíodh a fhios agat gur ábhar an-debhéasach é seo. Mar sin féin, i ficsean eolaíochta táimid ag iarraidh a shaothrú an féidir agus nach bhfuil gá a bheith ag iarraidh a bhuachan duaiseanna Nobel i exobiology.
Tá an plausibility eolaíoch seo go léir ina ábhar díospóireachta. Is iomaí réalteolaí (nó bitheolaithe ar an ábhar sin) a dhiúltú dul ró-fhada amach ar an mbarr a mholadh a réaltaí a bhfuil cuma geallta toisc go bhfuil an eolaíocht chomh fada ina infancy, d'fhéadfá chomh maith a ghlaoch ar an réamh-fetal. Mar sin féin, tá go leor teoiricí ann a thugann le fios cén cineál réaltaí a bheadh neamh-in ann saol a óstáil, nó ar a laghad a dhéanfadh sé thar a bheith dóchúil. Dá bhrí sin, is ar an údar a bheidh sé a chinneadh cé chomh fada is féidir leis na teoiricí reatha a bhrú chun tacú le scéal timpeall réalta áirithe. Déanaim iarracht cuimhneamh ar dhiúltú an eagarthóra clasaiceach don eolaíocht atá i bhfad uainn: 'Ní chiallaíonn seastacht an neamhchreidimh é a chrochadh ag an muineál go dtí go bhfaigheann sé bás.'
Tá trí phríomh-réimsí réalteolaíochta ann a chabhróidh leis na féidearthachtaí a bhaineann le réalta dóchúil a aimsiú a laghdú. Is é an chéad chabhair is mó, cé gurb é an ceann is casta, 'Clas Speictreach' an réalta agus trivia a bhaineann leis. Is é an dara ceann aois agus fad saoil an réalta, agus is é an tríú ceann tréithe ilréalta an chórais.
Diagram Hertzsprung Russell
Is dócha go bhfuil Diagram Hertzsprung Russell eolach ar dhuine ar bith a ghlac rang réalteolaíochta, nó a thóg riamh leabhar cineálach faoi réalteolaíocht. Seo leagan ó Thionscadal Réaltra Fíorúil Saor in Aisce Jim Smith, táim cinnte go bhfaca tú ceann den chineál céanna:
Seo athbhreithniú tapa. An níos gile a bhíonn réalta (de ghnáth ó achar tofa de 32.6 LY - 10 parsecs), is amhlaidh a bhíonn sé níos airde ar an gcairt. Tá Dimmer gar don bhun. Is é an ghné cothrománach den chairt ná an teocht -- réaltaí níos te ar chlé, réaltaí níos fuara ar dheis. Is dócha gur thug do chlas Astronomy 101 le fios cá bhfuil an ghrian (agus tá ponc buí mór ag beagnach gach diagram H-R i lár an phríomhsheasamh ag rá 'Táimid anseo', díreach mar a dhéanann an diagram seo). Is dócha gur múineadh duit ranganna speictreacha na réaltaí, O B A F G K M, agus is dócha go leor mnemonics chun cabhrú leat iad a mheabhrú, ó 'Ó Bí i do Bhean Féin Kiss Me' go dtí an clasaiceach a chúlghairm 'Ní fhaigheann ach buachaillí a ghlacann le feinimíneacht Kissed Meaningfully'. Tá na ranganna speictreacha roinnte ina n-uimhreacha, 0 níos teo ná 9, agus is réalta G2 é Sol. De ghnáth bíonn réaltaí O te/soiléir, agus bíonn réaltaí M fuar/damh, ach amháin na dwarfs bán mar Sirius B (te, damh) agus na supergiants dearga mar Betelguese (fhuar, geal). Is dócha gur múineadh duit freisin, de ghnáth le smugness aisteach, go bhfuil ár réalta réalta bán bán bán gan aon saintréithe idirdhealaithe a dhéanamh cosúil speisialta ar bhealach ar bith ar leith.
Tá sé go léir ag teacht ar ais, ceart? Tá cúpla rud ar an gcairt seo a dhéanann rudaí suimiúla do shealbhú pláinéid, agus beagnach gach ceann de shiúlann sé (mar sin a labhairt) timpeall ar an mais an réalta. Ní léirítear mais go sainráite ar an léaráid H-R, ach de ghnáth comhoiriúnach sé le teocht na réalta - bíonn mais níos mó ag na réaltaí ar fad ar an bpríomhsheasamh ar chlé de Sol agus bíonn mais níos lú ag na réaltaí ar dheis. Tá sé seo níos lú soiléir as an príomhshraith, nó ar a laghad ní aistrithe go díreach. Mar shampla, bíonn na dwarfs bán ag an taobh clé íseal i réimsí OBA, ach go ginearálta tá mais acu in aice leis an Sol, agus d'fhéadfadh roinnt giantán dearg (ní supergiants) a bheith in aice le mais Sol freisin, cé go dtagann siad ar dheis agus os cionn.
Toisc nach n-imíonn mais, ní bhíonn réaltaí ag dul trí an phríomhsheasamh de ghnáth. Tar éis na chéad chúpla faoin gcéad d'aois réalta (níos lú ná 5 faoin gcéad), déanann an réalta cobhsaíocht de ghnáth agus fanann sé sa phointe ghinearálta céanna ar an léarscáil H-R ar feadh suas le 90 faoin gcéad dá shaol. Fiú ag deireadh shaol Sol, nuair a leathnaíonn sé amach as an príomhsheasamh go giant dearg, d'fhéadfadh sé a bheith fós go teicniúil mar réalta rang G (nó b'fhéidir íseal-K) bunaithe ar a thimpeallacht, a shoiléire agus a mais. Tá roinnt réaltaí inathraithe ag bogadh beagán, áfach, agus tá teoiric ann go bhféadfadh 'titimí' beaga i luminosity na gréine a bheith mar thoradh ar na héadaí oighir (cé go bhfuil claonadh agam, tar éis dom éifeachtaí an timthrialla El Nino deireanach a fheiceáil, aontú leis an teoiric go raibh na héadaí oighir mar thoradh ar na Himalayas ag ardú ag bogadh an sruth scaird).
Chun críche córais phláinéide a d'fhéadfadh saol a chothabháil, b'fhéidir nach dteastaíonn uainn breathnú ró-fhada faoi réaltaí aicme K. Ag an bpointe sin, táimid ag féachaint ar mhais tipiciúil leath de Sol (le 0.2 uair an solas Sol), agus ritheann na réaltaí aicme M timpeall ceathrú cuid de mhais Sol (le 0.005 uair an solas Sol). Nuair a théann réaltaí i dtreo bhunscoil aicme K, bheadh ar aon phláinéid te dul níos gaire dá réalta óstach chun fanacht áit a bhfuil seans maith ag uisce le bheith ina leacht. Tá an baol ann go gcuirfidh sé seo an phláinéid i gcló go géar ionas go bhfanfaidh ceann dá thaobh i dtreo a réalta - rud a d'fhéadfadh fadhbanna aimsire agus teocht neamháisiúla a chur faoi deara. Ina theannta sin, tá go leor réaltaí ag lasadh, rud a fhágann go bhfuil riosca níos mó ann go mbeidh radaíocht mharfach ag cur plandaí in aice láimhe go rialta.
Ar an deireadh eile den scála, is dócha nach dteastaíonn uainn breathnú os cionn réaltaí rang F. Tá leibhéil arda radaíochta ultraivialait ag réaltaí O go A agus bíonn gaotha réalta ard acu a d'fhéadfadh atmaisféar a bhaint as. Tá réaltaí OBA claonadh chun rothlú go tapa chomh maith, agus tá teoiricí ann nach ndéanann réaltaí a rothlú go tapa go leor pláinéid a ghiniúint (nó b'fhéidir go bhfuil sé ar an mbealach eile agus rothlú go tapa réaltaí OBA toisc nach bhfuil go leor pláinéid acu chun an rothlú réalta a mhoilliú).
Ciallaíonn sé seo go bhfuil iarrthóirí dóchúla sna ranganna F, G, agus K, agus G b'fhéidir mar an ceann is fearr ach trí bheith i lár an raon. Mar a tharlaíonn sé, tá go leor níos mó réaltaí de mhais íseal ná réaltaí le mais níos airde. Ar gach 100 réalta, go staitisticiúil tá 67 réalta aicme M, 13 aicme K, 7 aicme G, 3 aicme F, agus b'fhéidir 1 aicme A (agus is dócha nach bhfuil aon cheann de na réaltaí aicme O agus B ann). As 400 billiún réalta sa réaltra, tugann sé seo dúinn thart ar 90 billiún iarrthóir FGK, níos lú ná cúig fiche faoin gcéad, agus seacht faoin gcéad de chineál G (26 billiún).
Is féidir aicmí speictrála a fho-roinn níos mó trí uimhreacha Rómhánacha bunaithe ar mhéid (a bhaineann le luminosity) ar a dtugtar scéim Yerkes:
I.a Supergiants Soiléir Ib Níos lú Soiléir Supergiants II Giants Soiléir III Giants gnáth IV Subgiants V Dwarfs VI Subdwarfs
Go ginearálta, tugtar stéarlanna rang V ar na stéarlanna bán mar go bhfuil siad i bhfad níos lú ná na ranganna Iab go IV. Mar sin féin, is mí-ainm staidrimh é an téarma 'dwarf' - 90% de na réaltaí a thagann i rang príomhsheasmhachta V agus is iad rang F agus níos fuíle. Mar gheall ar fhadhbanna le sliseanna agus le lasracha treochta, ba mhaith linn na réaltaí aicme V (cé gur féidir linn, b'fhéidir, a fháil amach le ball beag aicme IV faoi choinníollacha idéalacha). Soláthraíonn an réalta Canopus (sa chomhchruinniú réalta Argo) sampla maith chun rang Yerkes a sheiceáil; is réalta 'F0II' é Canopus. B'fhéidir go bhfuil F0 beagán toasty don saol, ach fós buí-bhán agus ar theorainn ár roghnú FGK inghlactha. Mar sin féin, lipéadaíonn an II é mar ollmhór geal agus i ndáiríre tá a trastomhas 65 uair níos mó ná Sol, le coróin foréigneach a astaíonn raidió X agus tonnta raidió láidir.
Tá sraith amháin eile de shonraí éagsúla ann a chuirtear roimh nó a chuirtear i gceangal le rang speictreach:
D Degenerate. Is gnamh bán é, mar atá i Sirius B, cineál DA2 d, de ghnáth gnamh dearg, mar atá i Proxima Centauri, cineál dM5e. Crócaigh
Tá rang V níos nua-aimseartha.
sd fo-dhuine (Yerkes VI na laethanta seo)
e astaíochtaí láidre (a léiríonn scamall gáis te mór tiubh nó coróin a chuairteann an réalta) m eilimintí trom annamh iomarcach (a mhéadaíonn miotail, uaireanta neamh-hidrigine / héiliam) n línte ionsú nebula (de ghnáth mar gheall ar rothlú ard réalta) neb speictream nebula measctha leis an réalta p gné shainiúil eile (de ghnáth iomarca eilimint nach raibh ag súil leis) réaltaí éagsúla línte laige (réaltaí sean, meatailtí-saor)
Má fhéachann duine ar fhéidearthachtaí réaltacha, mar shampla Canopus, d'fhéadfadh Sol a bheith cosúil le dwarf buí, beag, beag, gan spéis. Mar sin féin, ós rud é go bhfuil an rang speictreach nasctha le mais, tá níos mó mais ag Sol i ndáiríre ná an meánréalta. Toisc go bhfuil níos mó réaltaí K agus M ann ná aon réalta eile, déanann stádas G2 Sol é i ndáiríre níos gile ná an chuid is mó réaltaí. De réir na staitisticí iarbhír, is é Sol i ndáiríre níos gile, níos mó, níos te, agus níos annamh ná an chuid is mó de na réaltaí sa réaltra.
Má úsáidimid éabhlóid na Talún mar threoir, thóg sé thart ar 3 billiún bliain ar éabhlóid dul amach as an gcéim singil-chill nuair a d'fhorbair an saol. Thóg sé an t-am sin chun an t-atmaisféar a 'terraform' go ceann a sholáthraíonn ocsaigin saor in aisce, agus dá bhrí sin an cumas a thabhairt do shaol níos gníomhaí, ilchill. Thóg sé 540 milliún bliain ó 'Cambrian Explosion' an éabhlóid ilchilltiúil go Homo sapiens. Bhí go leor tús bhréagach ann seo mar gheall ar dhíothú mór, cuid acu tubaistí seach-thír (mar shampla tionchar féideartha Yucatan ag deireadh an Cretaceous), cuid acu a bhí de bhunadh talún (b'fhéidir go raibh an díothú trilobite mar thoradh ar athruithe aeráide pláinéadach mar gheall ar vulcanism mais i Sibéir anois). Tá tionchar ag go leor imeachtaí eile, ó timthriallta sunspot go díriú mór-roinn, ar éabhlóid ár speiceas measartha intleachtúil. B'fhéidir go raibh na himeachtaí seo riachtanach chun saol a d'fhéadfadh a bheith teoranta nó a bhí i gcomórtas le heolas éabhlóideach a bhaint amach. B'fhéidir dá mba nach ndearna tionchair Yucatan, go mbeadh dinosaur cliste, cónaitheach cliste tagtha chun cinn 50 milliún bliain níos luaithe ná mamaigh chliste.
Ar aon chuma, bunaithe ar an Domhan, is féidir linn a mheas thart ar 500 milliún bliain d'eabhlóid ilchillteach chun teacht ar dhaoine, móide 3 billiún bliain de shaol aon-chill, móide 500 milliún go 1 billiún bliain don Domhan chun scriosanna córas gréine a ionsú agus a fhuarachadh ó fhoirmiú. Is féidir linn tuairimíocht a dhéanamh ar athróg: B'fhéidir go bhféadfadh réalta a cruthaíodh ó néilóg ocsaigine / uisce ard a ghearradh amach billiún bliain nó dhó de terraforming aon-chill. B'fhéidir go bhfuil an t-eabhlóid níos tapúla agus níos iomaíche ar phláinéid ina bhfuil dromchla ar aon trian uisce in ionad trí cheathrú. Ar an drochuair don bitheolaí, tá na tuairimí seo teoranta go hiomlán. Ar an dea-scéal do scríbhneoir ficsean eolaíochta, ní chuireann teoiricí neamhthrócaithe bac i gcónaí ar fhorbairt na scéalta. Ó fhoirmiú pláinéad go saol cliste, glaoigh air 3 billiún bliain ar an deireadh íseal, b'fhéidir 6 billiún ar an deireadh ard. D'fhéadfadh saol neamh-intleachtúil a bheith i láthair i dtréimhse níos giorra ama, ach cuimhnigh go raibh saol an Domhain den chuid is mó slime, baictéir, agus algaí go dtí an Cambrian.
Bíonn tionchar ag mais ar dlús na réalta, rud a théann i bhfeidhm ar ráta cumasc na réalta, rud a théann i bhfeidhm ar aois féideartha na réalta. An A0 réalta cosúil Vega is dócha ach amháin maireachtáil ar feadh billiún bliain. D'fhéadfadh réalta M4 cosúil le Barnard a bheith beo ar feadh 50 billiún. Tá saol réalta ollmhór O beag; tá Alnitak (an chéad réalta ar chlé de chrios Orion) thart ar 6 mhilliún bliain d'aois agus tá hidrigin caite aige cheana féin. Le linn shaol Alnitak, tá an daonnacht tar éis éabhlóid ó díreach roimh Australopithecus afarensis (Lucy) go Homo sapiens. Ní dócha go raibh Alnitak níos mó ná cnapán i nebula san ré dineasúir.
Tá saolré réalta ag teorainn arís linn lenár rang speictreach FGK le haghaidh saol evolute féideartha, cé nach bhfuil sé as an gceist go mbeadh réalta neamh-FGK ina óstach do choilíneacht féideartha. Is féidir le lucht leanúna ficsean eolaíochta Larry Niven a thabhairt faoi deara gur coilíneacht ináitithe é Jinx timpeall Sirius A. Is réalta A1V é Sirius A, dhá oiread an mais Sol, faoi dhíon go saol gearr de b'fhéidir billiún agus leath bliain, agus is dócha go bhfuil sé ag pumpaíocht radaíocht UV go leor chun aon shaol a phiocadh ar phláinéid in aice láimhe. Mar sin féin, cruthaíonn scéalta Niven gur ghrian é Jinx i ndáiríre timpeall príomh-ghrian gáis. Cé nach luaitear é ina scéalta, d'fhéadfadh go mbeadh an bunscoil i bhfad go leor ó Sirius A ionas go mbeidh an radaíocht UV íseal. Is gnách go mbíonn na hiodrálacha gáis ina soláthraithe teasa; d'fhéadfadh Jinx a bheith i gcrios uisce-teochta lasmuigh den raon uisce leachtach gnáth Sirius A. Ina theannta sin, tá na speicis áitiúla ar Jinx, go príomha Bandersnatch, bunaithe mar fhoirmeacha beatha innealtóireachta géiniteacha a phlandaigh cine eile ann (tá Bandersnatch fiú díolmhaithe ó dhroch-mheathadh géiniteach mar gheall ar chromoisóim mhóra). Níl a fhios agam cé mhéad a bhí ar eolas nuair a scríobh Niven a chéad scéal Jinx, ach tá a scéal is féidir go teoiriciúil.
A thugann dúinn go dtí an cheist ar aois iarbhír réalta. Cé chomh sean is atá Sirius A? Má tá sé 100 milliún bliain d'aois, ansin is dócha nach bhfuil pláinéid críochnaithe ag foirmeáil (má tá siad ann ar chor ar bith) agus ní bheadh an réalta fiú thosaigh ag cumadh fós nuair a bhí na Slavers ag bogadh Bandersnatch timpeall. Ar an láimh eile, má tá Sirius A go leor aibí, a rá 1.2 billiún bliain d'aois, tá rudaí níos féideartha.
Ar an drochuair don réalteolaí (agus dúinn freisin, sa chás seo), níl bealach maith againn chun aois iarbhír réalta aonair a fháil amach (tá eisceachtaí ann, go háirithe i gcás Sirius). Tá a fhios againn go bhfuil Sol thart ar 5 billiún bliain d'aois toisc go bhfuil an méid sin de na carraigeacha ar an Domhan agus an Ghealach (agus, le déanaí, Mars). Tá teoiricí á thástáil faoi láthair: Is é ceann acu go laghdaíonn timthriallta spúnóg na gréine de réir mar a théann réalta in aois. Tá teoiric eile ag iarraidh a chinneadh cé mhéad hidrigine a d'aontaigh ó intéirneacha réalta; cosúil le tástáil Charbóin-14 nó Uráiniam, d'fhéadfadh sé seo a insint dúinn cé chomh fada agus a bhí réalta ar an bpríomhsheasamh trí mheastóireacht a dhéanamh ar an cóimheas idir héiliam agus hidrigine. Mar sin féin, níl aon bhealach iontaofa á úsáid faoi láthair chun aois réalta a aimsiú, seachas réaltaí an-óg (cosúil le baill Pliedes, atá fós ina néilíní breith) nó réaltaí an-aois (cosúil le Betelgeuse, atá ag cur le heilimintí trom, tar éis dó a bheith as Hidrigine agus Heiliam).
Córais Réaltaí Ilghnéitheacha
Is é an constaic réalta deiridh le bheith ag obair timpeall ná an láithreacht mhór réaltaí il. I measc na 100 réalta is gaire don Ghrian, tá 23 ina mbaill de chórais déthaobhacha nó il-réalta. D'fhéadfadh dinimic orbit na bpláinéid sna córais réalta ilbhliantúla seo a bheith deacair ar go leor cúiseanna.
Ní fhéadfaidh pléascóirí a bheith in áiteanna i gcúplaí gar. Tóg Castor, mar shampla, ceann de na réaltaí 'Twin' de Gemini agus a thaispeántar le súl nocht mar réalta ard A geal, te. Nuair a scrúdaítear go dlúth, is cosúil go bhfuil trí réalta ag Castor - péire le timthriall 400 bliain, timpeallaithe ag comhpháirtí lag 1000 AE ón péire inmheánach. Léiríonn anailís speictroscópúil i ndáiríre gur dhá réalta péireacha é Castor A atá ag rothlú ar a chéile i elipsis thart ar mhéid orbit Mercury, ag casadh uair amháin gach 9.2 lá. Is binary é Castor B freisin, le réaltaí níos dlúithe a dhéanann órbita gach 2.9 lá. Tá an réalta comhpháirtí lag ina dhúbailte freisin, dhá réalta M atá chomh gar go mbraitheann siad beagnach agus go n-orbitaíonn siad a chéile gach 20 uair an chloig. Casadh amach go bhfuil Castor ina chóras sé réalta, ceann ina mbeadh pláinéid is dócha nach mairfidh fada go leor chun a fhoirmiú fiú a chríochnú, gan trácht ar fhorbairt beatha.
Ní féidir le pláinéad, is dócha, órbita a choinneáil timpeall dhá réalta ag an am céanna; is é sin an t-eilifís nó ciorcal le dhá réalta laistigh den órbita. Ní dhéanann na réaltaí a bhíonn ag rothlú timpeall a chéile ach an iomarca pertubations orbital le haghaidh orbit chobhsaí, mura bhfuil an orbit an-mhór agus na dhá réalta lárnach an-ghar. Ní fhéadfadh na hoibríochtaí figiúr ocht, nó na hoibríochtaí casta babhta babhta eile, a bheith níos mó ná cúpla míle bliain i dtimpeallacht réalaíoch (d'fhéadfadh ocht figiúr a bheith seasmhach go sealadach le dhá réalta den mhais chéanna, i bhfad óna chéile, agus ag casadh go mall. Mar sin féin, tá na seansanna go bhfuil córas réalta den sórt sin dona go leor gan pláinéad renegade a chaitheamh isteach).
Is gnách go mbíonn déileálacha i bhfad níos fearr ó thaobh dinimiceach orbital de. Tóg Alpha Centauri, ár gcomharsanacht is gaire. Tá an córas seo i ndáiríre trí réalta. Is é Proxima Centauri (Alpha Centauri C) dM5e dwarf dearg os cionn 13 míle AE ó Alpha Centauri A agus B, ag déanamh orbita uair amháin gach cúpla céad míle bliain. Mar gheall ar an achar seo, is dócha nach gcuirfeadh Proxima isteach ar dinimic orbití aon phláinéid dlúth. Ní bhíonn Alpha Centauri A agus B chomh gar sin, freisin. Tá siad ag rothlú ar a chéile le tréimhse thart ar 80 bliain i elipsis leathan, ag teacht chomh gar le 11 AE (anuraidh ar orbit Saturn), ansin ag fáil 35 AE (anuraidh ar Neptune). Tá sé le feiceáil go bhféadfadh sé go mbeadh imlíneacha na bpláinéid faoi 3 AE in aghaidh na réalta cobhsaí. Ós rud é go bhfuil Alpha Centauri A G2V (de ghnáth géarghné de Sol), agus go bhfuil Alpha Centauri B níos fionnuar K0V, déanann sé seo go bhfuil sé indéanta go mbeadh pláinéad seasmhach sa chrios uisce leachtacha timpeall gach réalta! Samhlaigh cé chomh tapa agus a d'fhéadfadh taistil spáis a fhorbairt i gcóras le dhá phláinéid ináitithe nach bhfuil níos faide óna chéile ná leath ár gcóras gréine féin.
Ar an drochuair, ní fhéadfaidh rudaí a bheith chomh rósach sa chóras sin. I ár gcóras, tosaíonn crios Kuiper de astaróidigh agus deannaigh díreach tar éis Plútón (nó, b'fhéidir gurb iad Plútón agus Charon na rudaí Kuiper is mó, sa chás sin tosaíonn an crios díreach tar éis Neptune). Tá scamaill Oort de chómháin ann freisin ag tosú ag thart ar 10 míle AE ó Sol, ag síneadh amach go dtí 100 míle AE. Dá mbeadh an córas Centauri cosúil leis an gceann atá againn, d'fhágfadh Alfa Centauri A agus B go mbeadh siad ag dul timpeall a gcrios Kuiper gach 80 bliain agus bheadh Proxima ag scuabadh trí imeall na scamall Centauri Oort. Ní mór go mbeadh líon na gléasanna agus na n-astéaróidigh a bhíonn ag dul tríd an gcóras sin ollmhór, agus d'fhéadfadh tionchar a bheith acu go rialta ar aon phláinéid (an ndéanfadh sé seo an saol níos dóchúla nó níos lú?). Nó, b'fhéidir go raibh an córas glan go leor go luath ina shaol, cé go bhfuil fianaise ann go bhfuil pláinéad comhpháirtí super-Jovian ag Proxima Centauri mar gheall ar wobbles orbital.
Cad é an Cosúlacht leis an gCrios
Ag baint úsáide as na sonraí seo, cé na réaltaí is gaire a d'fhéadfadh saol a chothú, mura bhfuil sé i ndáiríre ag cruthú é? Lig dúinn a bhuail an 25 réalta is gaire, in ord, ag dul ar shiúl ó Sol.
Go pearsanta, tá mé ag cur in aghaidh an chórais Centauri le haghaidh saol cliste, cé gur maith liom é le haghaidh ilchillteach má tá sé sean go leor. Bheadh sé ina áit iontach chun a fháil ar ár cosa fliuch le coilíneacht nó dhó. Ba mhaith liom buille faoi thuairim go bhféadfadh go mbeadh an córas Centauri ró-chuid tionchair astaróide agus coimhéadaigh chun aon shibhialtacht buan a ghiniúint (cé nach bhfuil sé seo ach mo bhroinn agus is dócha nach gcuirfeadh stop orm scéal a scríobh faoi). Ba mhaith leis na radharcanna, áfach, a bheith iontach - dhá ghrian agus b'fhéidir coimhdeacha bliantúla nó míosúla.
Is iad na dhá réalta eile, Barnard's (M5V) agus Wolf 359 (an córas M6 de Star Trek Federation vs. Borg fame) dearga cineál M, nach bhfuil mé ag dul a bheith ag iarraidh ar feadh an tsaoil de chineál ar bith.
Gliese 411, ar a dtugtar UV Ceti freisin, (M2Ve, is dócha go bhfuil sé dúbailte) is cosúil go bhfuil sé gar do K, ach tá an cleachtadh míshásta seo aige go bhfuil sé ag fágáil níos mó ná roinnt uaireanta a chuid solais i gceann cúpla soicind.
Tá Gliese 65 ar an gcéad dul síos, agus is é sin dhá dwarf dearg 'dM5.5e' comhionann nach gcuirfeadh ach croí astrofíseiceach ar an gcroílár.
Sirius is é seo a leanas, is dócha ró-óg do shaol agus tá sé ró-te ar aon nós. Má bhí tús déanta ag an saol, buille faoi thuairim mé go raibh an córas iomlán sterilized nuair a thit Sirius B.
Lean dhá chánacha dearga eile, Gliese 729 (dM4.5e) agus Ross 248 (dM6e). Ní raibh aon rud ar bith ag an dá cheann acu.
Tá Epsilon Eridani (K2V, thart ar 10.7 LY amach) ar cheann de na réaltaí teorann suimiúla sin. Is réalta fionnuar é, agus ceann a lasann go leor, mar sin ní bhíonn rudaí go maith go ginearálta do na gonads. Mar sin féin, tá fianaise ann i mbrú an réalta go bhfuil pláinéad mór amháin ar a laghad timpeall air, agus fuair tástálacha infridhearg fáinne deannaigh. D'fhéadfadh go mbeadh Epsilon Eridani ina réalta óg díreach i gcéimeanna tosaigh phláinéid a fhoirmiú. Má thit na flareanna, d'fhéadfadh sé seo a bheith ina láthair chun féachaint air (i gceann billiún bliain nó mar sin). Mar sin féin, dá mbeadh rogha agam an raibh nó nach raibh sond a sheoladh anseo, ba mhaith liom an dáis a rolladh agus ceann a sheoladh amach.
Is iad Ross 128 (dM4.5), Gliese 866 (M5e dúbailte féideartha), agus GX Andromeda (doubailte, M2V agus M6Ve) an chéad cheann eile sa líne. Gach cool dearga, is dócha go leor sterile.
Tá Epsilon Indus ina dhiaidh sin, K5Ve (is féidir go bhfuil K4Ve beagán níos teo) thart ar 11.3 LY amach. Ní raibh mé in ann a fháil ar an eolas i bhfad ar an ngréasán ar aon nós faoi an réalta. Tá sé beagán fuar, ach d'fhéadfadh sé a bheith níos sine agus iarrthóir níos fearr ná Epsilon Eridani.
Tá 61 Cygni ar rang K dúbailte (K5Ve agus K7Ve) 11.3 LY ar shiúl freisin. Tá siad i bhfad óna chéile go leor (meán de 84 AE le timthriall 653 bliain) go bhféadfadh roinnt pláinéid a bheith ag an gceann acu. D'fhéadfadh 61 Cygni A a bheith ina athróg flare, agus is é sin an ceann is teo den péire. 61 Cygni B d'fhéadfadh a bheith ag tabhairt cuireadh, áfach, agus tá siad gar go leor go bhféadfadh sé a bheith gar go leor chun iarracht a dhéanamh dhá-ar-aon.
Tar éis 61 Cygni tá Gliese 71, damh dearg dúbailte (dM4 agus dM5) nach bhfuil aon spéis shoiléir ann.
D'fhéadfadh go mbeadh an bua againn le Tau Ceti, réalta G8Vp 11.4 LY ar shiúl. Tá an réalta seo beagán níos fuí ná an tSoil, ach fós réalta cineál G. Murab ionann agus Alpha Centauri A, níl Tau Ceti ina bhall de iomad. Má tá Tau Ceti sean go leor, is dócha gurb é seo an áit is fearr sna 50 réalta is gaire chun saol a lorg nó pláinéad deas compordach a aimsiú chun socrú air.
Is é Procyon an ceann deireanach as na 25 réalta is gaire agus is cosúil gur cousin níos fuaraí é Sirius. Ag F5IV-V, tá sé te agus mór, ach i ár raon réaltaí dóchúla. Tá réalta comhpháirtí bán-dhuanaigh ag Procyon, cosúil le Sirius, le timthriall de beagnach 41 bliain. Is é 14 AE an meán-achar ó na réaltaí, áfach, rud atá go leor gar - d'fhéadfadh go mbeadh aon phláinéid go leor gar do Procyon A, rud a d'fhéadfadh a bheith ró-te chun beatha.
Ceann de na rudaí áille atá ag an ngréasán ná go bhfuil sé níos éasca doiciméid 'bheo' a chruthú a d'fhéadfadh athrú de réir mar a théann an t-am ar aghaidh. Sa chuid seo, cuirfidh mé naisc le teoiricí nua faoi fhoirmiú pláinéid nó saol a d'fhéadfadh a bheith oiriúnach le téama an doiciméid seo.
Here Come the Suns -- (a chur leis an 19 Márta 00) Airteagal Scientific American. Tá beagnach dhá dhúisín pláinéid aimsithe againn ag rothlú na réaltaí eile faoi láthair, agus tá na cosúlachtaí idir na réaltaí a rothlú siad suimiúil: Is gnách go mbíonn na réaltaí saibhir i miotail (méitiltí nó eilimintí trom, do réalteolaí, aon eilimint seachas H nó He). Tabhair faoi deara Tau Ceti thuas - mar G8Vp, an 'p' a sheasann do mhéid mór ar leith de eilimint (Calciam, má chuimhním mo thaighde). An ndéanann sé seo Tau Ceti ina iarrthóir níos dóchúla ar phláinéid? Corollaire - réaltaí saibhir miotail claonadh a bheith in aice leis an croí na réaltra. Caithfidh réalta saibhir miotail a bheith déanta as iarsmaí supernova réalta marbh níos luaithe. D'fhéadfadh an fad is fearr a bheith i gceist amach ó chroí na réaltra (mhéideanna ard miotail, ach freisin go leor junk bombarding agus supernovae minice), ach ní ró-fhada amach (nuair nach bhfuil go leor tuama réalta níos sine ann). Cosúil le 'crios uisce' an chórais gréine, crios ina bhfuil an saol dóchúil mar gheall ar dóchúlacht uisce leachtacha, d'fhéadfadh go mbeadh 'crios pláinéid' réaltaí ag an réaltra áit a mbraitheann méid na miotail sna réaltaí nebulae ó uasmhéid. D'fhéadfadh go mbeadh an 'glimh phláinéid' seo go leor caol, agus d'fhéadfadh go mbeadh an Ghrian díreach i lár na cruinne.
Stáisiún Sonraí Réalta - (a cuireadh leis an 19 Márta 00) Stáisiún Sonraí Réalta. Tá 150% den ábhar miotail atá ag Alfa Centauri ar an nGrian, rud a d'fhéadfadh a bheith ina chomhartha maith d'fhoirmiú pláinéid. D'fhéadfadh sé a bheith 4.2 billiún bliain d'aois, rud a bheadh go maith do shaol ilchill. Sa réabhlóid ar an Domhan, d'fhéadfadh 4.2 billiún bliain a bheith idir an Bhriseadh Cambrian go dtí thart ar an am a tháinig na chéad ainmhithe talún (bugs, den chuid is mó, cosúil le millipedes), ach roimh chrainn agus fiú ferns - is é algaí ceirmeach an saol plandaí ar an talamh. Tá bunachar sonraí cluthar -- tá a lán faisnéise le haghaidh réaltaí gar, agus annotations mar a bhfuil an fhaisnéis a thagann ó.
Braitheann Aois Chromospheric -- (a cuireadh leis an 19 Márta 00) Airteagal Astrophysical Journal. Eolaíocht Dhéanach tromchúiseach: Conas a thomhas duine aois réalta? Is foilseachán Journal é seo ar nós imeachta a thástáil Don C. Barry de USC. Is alt acadúil é, tá tú tugtha faoi deara. Is é an teoiric go bhfuil réaltaí a luí a luí mar a aois, agus eject níos mó mais isteach ina gaoth gréine. Is féidir le botúin in aois a bheith suas le 20% uaireanta do réaltaí lár-saoil, ach d'fhéadfadh sé meastachán ballpark maith a thabhairt. Déanann an páipéar a aois a ríomh na réaltaí 115 F agus G Dwarf i gcluasair ar a dtugtar, cé gur cosúil go bhfuil an chatalóg a úsáideann sé chun na réaltaí a ainmniú ag éalú uaim (dáirítear go bhfuil uimhir ag gach réalta nach uimhir Gleise nó aon chatalóg eile a aithníonn mé - d'fhéadfadh sé a bheith ina chatalóg Woolley). Tintit suimiúil: sna réaltaí a breathnaíodh, bhí rást de fhoirmiú réalta ag críochnú thart ar 4 billiún bliain ó shin, agus rást eile ag tosú 400 milliún bliain ó shin. Go hiontach, níl go leor réaltaí sa ghrúpa seo idir 0.5 billiún agus 4 billiún bliain d'aois.
3-D Starmaps sraith go hiomlán fionnuar de leathanaigh ina bhfuil bunachair sonraí réalta agus pictiúir den chomharsanacht réalta áitiúil. Tá roinnt léarscáileanna i 3-D má tá na spéaclaí dearg-ghloine 3-D sin agat. Is féidir leat Catalog Gliese neamhchóirithe a fháil anseo, is bunachar sonraí é de na mílte réalta is gaire agus a gcineálacha speictreacha.
Leabhrán (don phríomh-phóipéar)
Réaltaí Tugann sé stair réalta amháin in aghaidh na seachtaine, de ghnáth ag lua méid, rang, agus trivia suimiúil eile.
Réaltaí na Bóthar Bainne leathanach faoi chineálacha speictreacha réaltaí.
An Tuairim Zeta Reticuli Ok, ar an dromchla, tosaíonn sé seo mar phlé faoi Betty agus Barney Hill (cuimhnigh, a éileamh a fuair siad abducted ag eachtrannaigh liath ar ais sna 60í) agus iniúchadh ar an bhféidearthacht go bhfuil an abducting Greys teacht ó Zeta Reticuli bunaithe ar chairt réalta Betty Hill tharraing amach as a intinn le linn hypnosis. Déantar an leathanach a dhíscaoileadh go tapa ina athphrint den Astronomy Magazine flame war idir Carl Sagan agus Steven Soter vs. a lán daoine eile a rinne iarracht a bheith níos 'sciúilte' faoin eachtra. (IMHO, tá an dá thaobh ag iomarca snáitheanna a bhfuil blinds orthu). Sa flotsam, áfach, tá teoiricí suimiúla faoi cad a thógann sé do réaltaí pláinéid a bheith iontu, agus na féidearthachtaí a bhaineann le pláinéid i gcórais réaltaí il. Léiríonn sé freisin cé chomh beag is atá an 'eolaíocht' seo ina luí.
An Clárú ar Spectra Réaltaí leathanach a phléann gnéithe níos lú eolais de chineálacha speictreacha, go háirithe réaltaí nach luíonn go leor leis an léaráid H-R.
Hertzsprung-Russell Diagram Ollscoil Oregon Athrónaim roinn nótaí ranga faoi H-R agus cineálacha speictreacha.
Astronomy103:H-R Diagram Ditto, ach is é seo Ollscoil George Mason.
Pleanóirí timpeall réaltaí déine A NASA 'Ask the Scientist' ceist agus freagra faoi phláinéid timpeall réaltaí il.
Centaurus plé ar an réalt Centaurus agus réaltaí laistigh de. Eolas suimiúil faoi Alpha Centauri.
Catalóg Dhéagránach Spéidearálach Más mian leat a fháil síos-agus-dirty sna sonraí faoi na réaltaí dhúbailte / il-aithní (mar shampla tréimhse orbital, leath-aiseanna móra, srl ...), ansin is é seo an bunachar sonraí duitse.
Hipparcos FAQ Hipparcos bhí sond na hEorpaigh a sheoladh amach i lár an chórais gréine chun breathnú ar réaltaí. Cosúil le catalóg Gliese, tháinig sé ar ais le bunachar sonraí de na mílte réalta le fadí dóchúla agus aicme speictreacha. Murab ionann agus chatalóg Gliese, bhí sé teoranta do réaltaí os cionn méid áirithe. Ciallaíonn sé seo go bhféadfadh sé a chaill an-ghar, ach réaltaí dim.
Hipparcos Na réaltaí is gaire Seo liosta de na réaltaí is gaire sa Chatalóg Hiparcos. Is féidir leat a fheiceáil gur chaill sé cuid a d'úsáid mé san aiste thuas -- is é sin toisc gur úsáid mé catalóg Gliese, lena n-áirítear réaltaí dim.
Alpha Centauri Níos mó sonraí Alpha Centauri, arna soláthar ag scríbhneoir Sci-Fi Robert J. Sawyer.
Réaltaí in aice láimhe Liosta eile de na réaltaí is gaire. Sílim go bhfuil an ceann seo Gliese bunaithe.
Plean Galasaice Fíorúil Saor in Aisce Níos mó plé H-R, agus ghoid mé an GIF H-R ón suíomh seo.
Scientific American's Ask the Expert leathanach faoi conas a insint cé chomh sean is atá réalta.
Rangacha speictreacha Sky & Telescope tuilleadh plé faoi H-R agus ranganna speictreacha.
Sun Vulcan ar ceart go leor, tá sé seo i ndáiríre plé faoi a réalta Spock is ó, ach tá sé ó Sky & Telescope agus pléann sé an fhéidearthacht na pláinéid timpeall córais réaltaí il.
Réaltaí in aice láimhe Is cuid é seo i ndáiríre de ghrúpa leathanaigh faoi léirmhíniú Bíobla, ach luaitear ann an phlé suimiúil faoi Sirius a thuairiscítear 2000 bliain ó shin mar réalta dearg.
Damháin Bán Plé faoi dheireadh saoil na Príomh-sreangtha, ó Ollscoil Stáit Ohio
An Dogon agus Sirius Ó Fhoras an Sceptic, plé faoi threibh na Dogon san Afraic agus Sirius.
Pleanóirí Eacnamaíocha Liosta Pleanóirí a aimsíodh ag Misean Darwin timpeall réaltaí in aice láimhe (de ghnáth, ceangail deannaigh, cosúil le Vega, nó super-jovians cosúil le Bernards).
(Uasdátú 20 Márta 2000 - socraíodh roinnt rudaí a d'éirigh liom a chur in iúl maidir le hainmniúcháin dwarf agus subdwarf.)
(Uasdátú 19 Márta 2000 - socraíodh roinnt nasc briste, lipéad mícheart de Canopus, athraíodh roinnt focail a chuir isteach orm, roinn teoiric breise)
Ar ais go dtí Sáruithe
Ar Ais go Ficsean Eolaíochta


||This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (June 2009)|
Tabatabaei House, early 1800s, Kashan. A fine example of traditional Persian architecture.
|Time zone||IRST (UTC+3:30)|
|• Summer (DST)||IRDT (UTC+4:30)|
Kashan (Persian: کاشان, also Romanized as Kāshān; also known as Kachan) is a city in and the capital of Kashan County, in the province of Isfahan, Iran. At the 2006 census, its population was 248,789, in 67,464 families.
The etymology of the city name comes from the Kasian, the original inhabitants of the city, whose remains are found at Tapeh Sialk dating back 9,000 years; later this was changed to "Kashian", hence the town name. Between the 12th and the 14th centuries Kashan was an important centre for the production of high quality pottery and tiles. In modern Persian, the word for a tile (kashi) comes from the name of the town.
Kashan is cited in the neighbourhood of two of highest peaks of Karkas chain, Mount Gargash to the southwest of Kashan (the home of Iran national observatory, the largest astronomical telescope of Iran) and Mount Ardehaal in the west of Kashan, also known as "Damavand of Kashan" and the highest peak of Ardehaal mountains (end part of Karkas chain in central Iran).
Archeological discoveries in the Sialk Hillocks which lie 4 km west of Kashan reveal that this region was one of the primary centers of civilization in pre-historic ages. Hence Kashan dates back to the Elamite period of Iran. The Sialk ziggurat still stands today in the suburbs of Kashan after 7,000 years.
By some accounts although not all Kashan was the origin of the three wise men who followed the star that guided them to Bethlehem to witness the nativity of Jesus, as recounted in the Bible. Whatever the historical validity of this story, the attribution of Kashan as their original home testifies to the city's prestige at the time the story was set down.
Abu-Lu'lu'ah/Pirouz Nahāvandi, the Persian soldier who was enslaved by the Islamic conquerors and eventually assassinated the caliph Umar al-Khattab in AH 23 (643/4 CE), reportedly fled to Kashan after the assassination and lived there some years before being finally caught and executed. His tomb is one of Kashan's conspicuous landmarks (see gallery below).
Sultan Malik Shah I of the Seljuk dynasty ordered the building of a fortress in the middle of Kashan in the 11th century. The fortress walls, called Ghal'eh Jalali still stand today in central Kashan.
Kashan was also a leisure vacation spot for Safavi Kings. Bagh-e Fin (Fin Garden), specifically, is one of the most famous gardens of Iran. This beautiful garden with its pool and orchards was designed for Shah Abbas I as a classical Persian vision of paradise. The original Safavid buildings have been substantially replaced and rebuilt by the Qajar dynasty although the layout of trees and marble basins is close to the original. The garden itself however, was first founded 7000 years ago alongside the Cheshmeh-ye-Soleiman. The garden is also notorious as the site of the murder of Mirza Taghi Khan known as Amir Kabir, chancellor of Nasser-al-Din Shah, Iran's king in 1852.
The earthquake of 1778 leveled the city of Kashan and all the edifices of Shah Abbas Safavi, leaving 8000 casualties. But the city started afresh and has today become a focal tourist attraction via the numerous large houses from the 18th and 19th centuries, illustrating the finest examples of Qajari aesthetics.
Although there are many sites in Kashan of potential interest to tourists, the city remains largely undeveloped in this sector, with fewer than a thousand foreign tourists per year. Qamsar and Abyaneh are notable towns around Kashan, which attract tourists all year around. The nearby town of Niasar features a man-made cave and fireplace of historical interest.
Kashan is internationally famous for manufacturing carpets, silk and other textiles. Kashan today houses most of Iran's mechanized carpet-weaving factories, and has an active marble and copper mining industry. Kashan and suburbs have a population of 400,000.
Kashan's architectural sights include:
- Agha Bozorg Mosque
- Āmeri House
- Boroujerdi House
- Jalali castle
- Tabātabāei House
- Abbāsi House
- Attarha House
- Al-e Yaseen House
- Sultan Amir shrine and bath
- 40 Dokhtaran Fortress
- Pirouz Nahavandi/Abu-Lu'lu'ah Shrine (the assassin of islam 's second Caliph)
- Fin Garden
- Fin Bathroom
- Ghal'eh jalali
- Jameh Mosque of Kashan
- Kashan Bazaar
- Meydan Mosque
- Tabriziha Mosque
- Timcheh Amin-o-dowleh
Colleges and universities in Kashan include:
- Sohrab Sepehri
- Ghyath ad-Din Jamshid Kashani
- Mohammad-Nabi Sarbolouki
- Ustad Ali Maryam
- Muhsen Feyz Kashani
- Yedidia Shofet the former chief rabbi of Iran and the worldwide spiritual leader of Persian Jewry.
- Uriel Davidi the former chief rabbi of Iran and the worldwide spiritual leader of Persian Jewry.
- Isaac Larian is the Chief Executive Officer of MGA Entertainment
- David Alliance, Baron Alliance Businessman and a Liberal Democrat politician in the United Kingdom.
- Seyyed Hossein Nasr, Leading Islamic Philosopher and exponent of the Perennial Philosophy
- Iranian Architecture
- Kashan rug
- List of the historical structures in the Isfahan province
- Sialk - Kashan's ancient architecture.
- Traditional Persian residential architecture
- Kashan can be found at GEOnet Names Server, at this link, by opening the Advanced Search box, entering "-3069961" in the "Unique Feature Id" form, and clicking on "Search Database".
- "Census of the Islamic Republic of Iran, 1385 (2006)". Islamic Republic of Iran. Archived from the original (Excel) on 2011-11-11.
- Elgood, Cyril. A Medical History of Persia and the Eastern Caliphate: From the Earliest Times Until the Year A.D. 1932. Cambridge Library Collection - History of Medicine. Cambridge University Press, 2010. ISBN 1108015883 p. 34
|Wikivoyage has a travel guide for Kashan.|
|Wikimedia Commons has media related to Kashan.|

Tá liosta tagairtí san alt seo, ach níl a fhoinsí soiléir mar níl go leor luaite i líne ann. (Meitheamh 2009)
Teach Tabatabaei, go luath sna 1800í, Kashan. Sampla den scoth de ailtireacht traidisiúnta na Peirsis.
 Ceantar ama
• Samhradh (DST)  IRDT (UTC+4:30)
Is cathair i gContae Kashan (Persan, a dtugtar Kachan freisin) i gCúige Kashan, i gCúige Isfahan, an Iaráin. Ag daonáireamh 2006, bhí 248,789 duine ina gcónaí ann, i 67,464 teaghlach.
Tagann eitimolaíocht ainm na cathrach ó na Kasian, áitritheoirí bunaidh na cathrach, a bhfuil a gcuid fágtha le fáil ag Tapeh Sialk a théann siar 9,000 bliain; ina dhiaidh sin athraíodh é seo go "Kashian", dá bhrí sin ainm na cathrach. Idir an 12ú agus an 14ú haois bhí Kashan ina ionad tábhachtach le haghaidh táirgeadh ceirmeacha agus tíleanna ardchaighdeáin. Sa Phársas nua-aimseartha, tagann an focal le haghaidh tíle (kashi) ó ainm na cathrach.
Tá Kashan luaite i gcomharsanacht dhá cheann de na buaic is airde de shraith Karkas, Beinn Gargash go dtí an iarthuaisceart de Kashan (áit chónaithe na réadlann náisiúnta na hIaráine, an teileascóp réalteolaíoch is mó san Iaráin) agus Beinn Ardehaal i dtuaisceart Kashan, ar a dtugtar "Damavand of Kashan" agus an buaic is airde de na sléibhte Ardehaal (cuid deiridh de shraith Karkas i lár na hIaráine).
Léiríonn fionnachtana seandálaíochta sna Sialk Hilllocks atá suite 4 km siar ó Kashan go raibh an réigiún seo ar cheann de na príomh-lár sibhialtachta sna réamhtheachtacha. Dá bhrí sin, téann Kashan siar go dtí tréimhse Elamite na hIaráine. Tá ziggurat Sialk fós i láthair na huaire i mbruachbhailte Kashan tar éis 7,000 bliain.
De réir roinnt cuntais, cé nach raibh Kashan go léir, ba é bunús na dtrí fhear bhreithneacha a lean an réalta a threoraigh iad go Bethleimh chun breith Íosa a fheiceáil, mar a thuairiscítear sa Bhíobla. Cibé an bailícht stairiúil atá ag an scéal seo, léiríonn an t-aithris ar Kashan mar a dtír dhúchais bunaidh go raibh cáil ar an gcathair ag an am a leagadh síos an scéal.
Abu-Lu'lu'ah / Pirouz Nahāvandi, an saighdiúir Peirsis a bhí faoi sclábhaíocht ag na conquerors Ioslamach agus a d'amhlaigh sa deireadh an caliph Umar al-Khattab i AH 23 (643/4 CE), tuairiscíodh gur theith sé go Kashan tar éis an mharú agus maireann sé ann roinnt blianta sula bhfaightear é agus a fhorghníomhú sa deireadh. Tá a uaigh ar cheann de na suaitheanta is suntasaí i Kashan (féach gailearaí thíos).
D'ordaigh Sultan Malik Shah I den dynasty Seljuk tógáil daingne i lár Kashan sa 11ú haois. Tá ballaí an daingne, ar a dtugtar Ghal'eh Jalali, fós i lár Kashan inniu.
Ba áit saoire saoire é Kashan do Ríthe Safavi freisin. Is é Bagh-e Fin (Ghairdín Fin), go sonrach, ceann de na gairdíní is cáiliúla san Iaráin. Dearadh an ghairdín álainn seo lena linn agus le torthaí do Shah Abbas I mar fhís pharsúil na Peirsí ar pháras. Cuireadh na foirgnimh Safavid bunaidh in ionad go mór agus atógadh iad ag an gcineál Qajar cé go bhfuil leagan amach na gcrann agus na mboscaí marmair gar don bhunús. Bunaíodh an ghairdín féin 7000 bliain ó shin in éineacht leis an Cheshmeh-ye-Soleiman. Tá an ghairdín cáiliúil freisin mar an suíomh a maraíodh Mirza Taghi Khan ar a dtugtar Amir Kabir, seansailéir Nasser-al-Din Shah, rí na hIaráine i 1852.
Chuir crith talún 1778 cathair Kashan agus gach foirgneamh de Shah Abbas Safavi ar an leibhéal, ag fágáil 8000 caillteanas. Ach thosaigh an chathair as nua agus tá sé anois ina mhealladh turasóireachta lárnach trí na tithe móra iomadúla ón 18ú agus ón 19ú haois, ag léiriú na samplaí is fearr de áilleacht Qajari.
Cé go bhfuil go leor suíomhanna i Kashan a d'fhéadfadh a bheith spéisiúil do thurasóirí, tá an chathair fós gan fhorbairt den chuid is mó sa earnáil seo, le níos lú ná míle turasóir eachtrach in aghaidh na bliana. Is bailte suntasacha iad Qamsar agus Abyaneh timpeall Kashan, a mheallann turasóirí ar feadh na bliana. Tá uaimh agus teallach de spéis stairiúil déanta ag an duine i mbaile in aice láimhe Niasar.
Tá cáil idirnáisiúnta ar Kashan as carpets, síoda agus teicstílí eile a mhonarú. Sa lá atá inniu ann tá an chuid is mó de mhonarcha meicniúla cóipeála-teipithe na hIaráine i Kashan, agus tá tionscal mairnéala agus mianadóireachta copair gníomhach ann. Tá daonra de 400,000 ag Kashan agus fo-bhaileanna.
I measc na n-amhairc ailtireachta atá i Kashan tá:
- Mosque Agha Bozorg
- Áras Ámeri
- Teach Boroujerdi
- Caisleán Jalali
- Teach Tabātabāei
- Teach Abbāsi
- Teach Attarha
- Teach Al-e Yaseen
- Naomh agus folctha Sultan Amir
- 40 Dochtaran Fortress
- Pirouz Nahavandi/Abu-Lu'lu'ah Shrine (an marú an dara Caliph Ioslam)
- Gairdín Finne
- Fin Bathroom
- Ghal'eh jalali
- Mosque Jameh de Kashan
- Kashan Bazaar
- Mosque Meydan
- Mosque Tabriziha
- Timcheh Amin-o-dowleh
I measc na coláistí agus na n-ollscoileanna i Kashan tá:
- Sohrab Sepehri
- Ghyath ad-Din Jamshid Kashani
- Mohammad-Nabi Sarbolouki
- Ustad Ali Maryam
- Muhsen Feyz Kashani
- Yedidia Shofet an iar-príomh-raibín na hIaráine agus an ceannaire spioradálta domhanda na Giúdachas Peirsis.
- Uriel Davidi an iar-príomh-raibín na hIaráine agus an ceannaire spioradálta domhanda na Giúdachas Peirsis.
- Is Isaac Larian an Príomh-Oifigeach Feidhmiúcháin de MGA Entertainment
- David Alliance, Baron Alliance Ghnó-fhear agus polaiteoir Daonlathach Liobrálach sa Ríocht Aontaithe.
- Seyyed Hossein Nasr, Saineolaí Ioslamach Treoir agus exponsor na Fealsúnacht Perennial
- Ailtireacht na hIaráine
- Rannóg Kashan
- Liosta de na struchtúir stairiúla i gCúige Isfahan
- Sialk - ailtireacht ársa Kashan.
- Ailtireacht chónaithe traidisiúnta Peirsis
- Is féidir Kashan a fháil ag Seirbhéir Ainmneacha GEOnet, ag an nasc seo, trí bhosca Cuardaigh Ardteicneolaíochta a oscailt, "-3069961" a iontráil sa fhoirm "Aitheantas Feidhmchláir Aonair", agus cliceáil ar "Bainise Sonraí Cuardaigh".
- "Daonáireamh Phoblacht Ioslamach na hIaráine, 1385 (2006)". Poblacht Ioslamach na hIaráine. Archaithe ón bhunachar (Excel) ar 2011-11-11.
- Elgood, Cyril. A Medical History of Persia and the Eastern Caliphate: From the Earliest Times Until the Year A.D. 1932. (Scéal Leighis na Peirsis agus an Caliphate Thoir: Ó na hAmha is Tréad go dtí an Bliain A.D. 1932). Bailiúchán Leabharlainne Cambridge - Stair na Leigheas. Foilseachán Ollscoil Cambridge, 2010. ISBN 1108015883 l. 34
Tá treoir taistil ag Wikivoyage do Kashan.
Tá meáin ag Wikimedia Commons a bhaineann le Kashan.


The laser goes from the weapon of tomorrow to the weapon of today as the US Navy announces the completion of its successful deployment of the Office of Naval Research's (ONR) Laser Weapon System (LaWS). The deployment is the first on a US Naval vessel and took place on the USS Ponce (LPD-15) in the Arabian Gulf from September to November of this year.
Developed as part of the ONR's Solid-State Laser-Technology Maturation program, LaWS is part of the US military's effort to develop a cost-effective, combat-ready laser prototype. While LaWS is not the first laser weapon ever to have been deployed, it is the first on a US Naval vessel and is a considerable advance on previous laser weapons.
According to the Navy, LaWS is capable of handling small attack boats, unmanned aerial vehicles (UAV), and other asymmetric targets, and has a wide range of settings, ranging from the ability to "dazzle" people and sensors without destroying them, to being able to disable or destroy targets. It also has the advantages of being able to engage targets at the speed of light, not requiring ammunition, being able to operate so long as power is available, and has a cost-per-round of a about a dollar per shot – which is a considerable saving in an area when munitions can cost thousands or even millions apiece.
According to Rear Adm. Matthew L. Klunder, chief of naval research, this helps to ensure that the US Navy and Marines are never in a "fair fight."
This year's deployment was a joint mission by ONR, Naval Sea Systems Command, Naval Research Laboratory, Naval Surface Warfare Center Dahlgren Division and private industry. During its time at sea, the laser was used against a variety of targets, such as small boats and other moving targets at sea, and also managed to knock a flying Scan Eagle UAV out of the sky.
The Navy says that the LaWS exceeded expectations not only in reliability, but in maintainability as well, and it integrated seamlessly with the Ponce's existing defense systems. In addition, sailors aboard said that it performed flawlessly in all weathers, including high winds, heat and humidity.
The deployment is part of the system's development following demonstrations in 2011 and 2012. The results of this year's deployment will be used to assess the progress of the program and determine future development timeframes. The ONR sees the system as not only applicable for sea duty, but also as an effective defense against airborne and ground-based weapon systems.
"Laser weapons are powerful, affordable and will play a vital role in the future of naval combat operations," says Klunder. "We ran this particular weapon, a prototype, through some extremely tough paces, and it locked on and destroyed the targets we designated with near-instantaneous lethality."
The video below shows the US Navy weapon in action.
Source: US Navy
Want a cleaner, faster loading and ad free reading experience?
Try New Atlas Plus. Learn more

Téann an léasair ó arm an lae amárach go arm an lae inniu agus an Cabhlach Mheiriceá ag fógairt go bhfuil an córas arma léasair (LaWS) de chuid Oifig na Taighde Cabhlaigh (ONR) curtha i bhfeidhm go rathúil. Is é an chéad imscaradh ar long Seandálaigh na Stát Aontaithe agus tharla sé ar an USS Ponce (LPD-15) sa Ghleann Arabach ó Mheán Fómhair go Samhain na bliana seo.
Forbraíodh é mar chuid de chlár Matúrtha Teicneolaíochta Léasair Sóid-Stát an ONR, is cuid de iarrachtaí arm na Stát Aontaithe é LaWS chun prototaip léasair costéifeachtach, réidh le haghaidh cogaidh a fhorbairt. Cé nach é LaWS an chéad arm léasair a cuireadh i bhfeidhm riamh, is é an chéad cheann ar long Cabhlaigh na Stát Aontaithe é agus is é sin dul chun cinn suntasach ar airm léasair roimhe seo.
De réir an Cabhlaigh, tá LaWS in ann báid ionsaithe beaga, feithiclí aeir gan foireann (UAV), agus spriocanna neamhréireacha eile a láimhseáil, agus tá raon leathan socrú ann, óna chumas daoine agus braiteoirí a "dazzle" gan iad a scriosadh, go dtí a bheith in ann spriocanna a dhíchumasú nó a scriosadh. Tá na buntáistí freisin aige a bheith in ann spriocanna a ionsaí ag luas na solais, gan gunnaí a bheith ag teastáil, a bheith in ann oibriú chomh fada agus a bhíonn cumhacht ar fáil, agus tá costas in aghaidh an raonta de thart ar dollar in aghaidh an bhratach  is coigilt shuntasach é i limistéar nuair is féidir le munitions na mílte nó fiú na milliúin a chosc.
De réir an Rear Admiral Matthew L. Klunder, ceann taighde na mara, cabhraíonn sé seo le cinntiú nach bhfuil Cabhlach na Stát Aontaithe agus Maraigh riamh i "cath cothrom".
Ba misean comhpháirteach é imscaradh na bliana seo ag ONR, Cinn Córais Mhuirí Mhuirí, Saotharlann Taighde Mhuirí, Ionad Cogaidh Dromchla Mhuirí Roinn Dahlgren agus tionscal príobháideach. Le linn a chuid ama ar muir, baineadh úsáid as an léasair i gcoinne spriocanna éagsúla, mar shampla báid bheaga agus spriocanna bogtha eile ar muir, agus d'éirigh leis freisin UAV Scan Eagle eitilte a bhualadh as an spéir.
Deir an Cabhlach gur sháraigh an LaWS ionchais ní amháin i iontaofacht, ach i gcothabháil chomh maith, agus chomhtháthaigh sé go huathoibríoch le córais cosanta atá ann cheana féin ag Ponce. Ina theannta sin, dúirt muirí ar bord go ndearna sé go foirfe i ngach aimsir, lena n-áirítear gaotha ard, teas agus taise.
Tá an cur i bhfeidhm mar chuid d'fhorbairt an chórais tar éis taispeántais in 2011 agus 2012. Úsáidfear torthaí an imscaradh i mbliana chun dul chun cinn an chláir a mheas agus chun amchláir forbartha sa todhchaí a chinneadh. Feictear sa ONR nach bhfuil an córas infheidhme ar dhleacht farraige amháin, ach mar chosaint éifeachtach i gcoinne córais arm aer- agus talamh-bhunaithe.
"Tá airm léasair cumhachtach, inacmhainne agus beidh ról ríthábhachtach acu i ngníomhaíochtaí comhraic muirí sa todhchaí", a deir Klunder. "Rith muid an t-arm seo, próta-amhrán, trí roinnt céimeanna an-deacair, agus d'fhág sé agus scrios na spriocanna a ainmníomar le bású beagnach láithreach".
Taispeánann an físeán thíos arm Mhuirí na SA i ngníomh.
Foinse: Cabhlach na SA
Ar mhaith leat taithí léitheoireachta níos glaine, níos tapúla agus saor ó fhógraí?
Bain triail as Atlas Nua Plus. Faigh tuilleadh eolais


Here’s how you’d pass a steam main over a steel beam:
The pitch is in the direction of the flow. The steam goes over the beam through a pipe that’s the same size as the main. The condensate goes under the beam through a pipe which you’d size the same as a wet return (see chart for wet-return sizing).
Make sure the centerline of the main on the downhill side of the beam is at least 1 inch lower than the centerline of the main on the uphill side. That’s so condensate will drain out of the lower pipe without backing up into the uphill steam main.
If you can’t get over the beam, you might go through it. If that’s not possible, just go under it by dropping the entire main.
If you can’t do that and have to bring the main up again, try this:
Drip the main into a wet return if one is available. That’s always best. But if you don’t have a wet return nearby, you can get a little creative and do this:
This is a steam siphon. Make sure you don’t insulate the ¾-inch siphon piping (but make sure the main is insulated). Condensate will flow downhill and fill the water seal at the bottom of the siphon. Steam pressure in the main will push down on the water seal and drive the condensate up the pipe. Some steam will also go up the siphon pipe.
Since you don’t insulate the siphon piping, the steam above the water seal will condense faster than the steam in the main. The short length of fintube radiation above the main (between the inverted loop and the check valve) speeds up the condensing process. That drops the pressure above the water seal in the siphon and draws condensate up the pipe. The check valve holds the siphon while it’s forming.
The siphon usually forms and breaks several times before it’s established, but once it is established, it works just like a hose draining a swimming pool. The siphon draws the condensate up over the hump, through the swing-check valve, and dumps it back into the steam main. Make sure you have about a foot of height above the check valve. You’ll need this to build some static pressure. The combined static pressure and steam pressure will be enough to open the check against the downstream steam pressure. Enter the main from the siphon on a 45-degree angle, as you would in a one-pipe system.
The main drawback of the siphon is that it only works when the steam pressure is up. And you do need more steam pressure than usual to make it work.

Seo mar a dhéanfá píopa gaile a rith thar dromchla cruach:
Tá an t-alt i dtreo an sruth. Téann an gaile thar an mbraon trí phíopa atá den mhéid céanna leis an bpríomhphíopa. Téann an tiúchan faoi bhraon trí phíopa a bhfuil an méid céanna aige le tiúchan fliuch (féach an chairt le haghaidh méid tiúchan fliuch).
Déan cinnte go bhfuil lárlíne an phríomhchlaí ar thaobh na lúb ag titim ar a laghad 1 orlach níos ísle ná lárlíne an phríomhchlaí ar thaobh na lúb ag titim. Tá sé sin ionas go mbeidh condensate draenáil amach as an píopa níos ísle gan cúltaca suas isteach sa príomh-steam suas.
Mura féidir leat dul thar an lúb, d'fhéadfadh tú dul tríd. Mura bhfuil sé sin indéanta, ach dul faoi sé ag titim an príomh iomlán.
Mura féidir leat é sin a dhéanamh agus go gcaithfidh tú an príomh-uas a thabhairt suas arís, déan iarracht seo:
Cuir an príomh-uisce isteach i n-aisghabháil fliuch má tá ceann ar fáil. Is é sin an rud is fearr i gcónaí. Ach mura bhfuil aon aisíocaíocht fliuch agat in aice láimhe, is féidir leat a bheith cruthaitheach agus é seo a dhéanamh:
Is siphon gaile é seo. Déan cinnte nach n-aonaíonn tú an píopa siúbtha 3⁄4- orlach (ach déan cinnte go bhfuil an príomhphíopa inslithe). Beidh an tiúchan ag sreabhadh síos agus líonfaidh sé an séala uisce ag bun an siphon. Cuirfidh brú gaile sa phríomh-uisce síos ar an séala uisce agus tiocfaidh an tiúchan suas an píopa. Téann roinnt gaile suas an píopa siphon freisin.
Ós rud é nach bhfuil tú inslithe an siphon píopaí, an t-uisce os cionn an séala uisce beidh condense níos tapúla ná an t-uisce sa phríomh. Déanann an fad gearr de radaíocht fintube os cionn an phríomhshrutha (idir an lúb inverte agus an comhla seiceála) an próiseas tiúchan a luathaithe. Laghdaíonn sé sin an brú os cionn an séala uisce sa siphon agus cuireann sé tiúchan suas an píopa. Coinníonn an comhla seifeadta an siphon agus é ag cruthú.
De ghnáth, cruthaíonn an siphon agus briseann sé roinnt uaireanta sula bhunaítear é, ach nuair a bhunaítear é, oibríonn sé díreach mar shlóigh a shlaodann linn snámha. Tarraingíonn an siphon an tiúchan suas thar an gcnoc, tríd an bhalbón seiceála swing, agus dumpann sé ar ais isteach sa phríomh-bhruith. Déan cinnte go bhfuil thart ar 30 cm ar airde os cionn an bhalbhaice cúlchiste. Beidh ort é seo a thógáil roinnt brú statach. Beidh an brú statach agus an brú gaile comhcheangailte leordhóthanach chun an seiceáil a oscailt i gcoinne an brú gaile thíos an sruth. Téigh isteach sa phríomh-srian ón siphon ar uillinn 45 céim, mar a dhéanfá i gcóras aon-píopa.
Is é príomh-mhéara an siúlóid ná nach n-oibríonn sé ach nuair a bhíonn brú gaile suas. Agus ní mór duit níos mó brú gaile ná mar is gnách chun é a dhéanamh ag obair.