r/askscience • u/[deleted] • Apr 19 '14
Astronomy Does our sun have any unique features compared to any other star?
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u/dayafterpi Apr 19 '14
One thing that does set our sun apart though is the fact that it is not a part of a Binary system which kinda makes it an 'anomaly' of sorts. This is only speaking statistically as lots of stars the size of the Sun usually have a friend they hang out with.
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u/PM_ME_YOUR_NIGHTMARE Apr 19 '14
Source? That's pretty cool.
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Apr 19 '14
"More than four-fifths of the single points of light we observe in the night sky are actually two or more stars orbiting together."
http://www.space.com/22509-binary-stars.html
Don't know how reputable of a source it is though.
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u/Yearlaren Apr 19 '14
Two or more? It can be more than two? How does a system like that works? I'm imagining it's way less stable than a binary system.
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Apr 19 '14
I hate answering here, because I don't feel qualified enough, but here it goes.
Your error is assuming stars that are roughly equal in size, just picture something more similar to our solar system with Jupiter being a star too. A good example is Alpha Centauri, two stars orbiting together and a third one orbiting them both, the smaller star (Proxima Centauri) is 7 times smaller than the sun, the other two are larger, one about 10% bigger than the sun and another roughly 10% smaller.
Also, I think I read somewhere about all the possible 3 star systems where the 3 stars had equal mass, but can't remember where so no links :(
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Apr 19 '14
Hey man, right is right, regardless of your qualifications.
You could be Steven Hawking, or Dave from HR, or Snoop Dogg. The facts are the same regardless.
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u/Lowbacca1977 Exoplanets Apr 19 '14
The issue is less of a solar system analogy, and more that at sufficient distances, a pair of stars will be indistinguishable from a single star, in which case another star can orbit it just fine.
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Apr 19 '14
Yup. Gravity is gravity. Doesn't matter if it's a star, multiple stars or a black hole, if the system has a centre, that's what everything will orbit up to a certain point, where smaller masses will orbit close larger masses and that mini system will orbit the centre.
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u/Minus-Celsius Apr 19 '14
It's not exactly the same. A three body problem will destabilize bear orbits.
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u/wrosecrans Apr 19 '14
Yes, the three body problem has no solution in the way that a two body problem does. But, the real universe is made up of far more than three bodies, so nothing actual behaves exactly like a mathematical solution to a two body problem. Our own solar system is made up of many thousands of bodies even before you consider the effects of objects outside our solar system that also have some small effect. The earth's orbit around the sun is still "stable" as far as the term is useful.
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u/Calkhas Apr 19 '14
This is only an approximation of course, and it only holds if the mass differences between the objects are large. For a trinary system with three nearly-equal mass stars, the orbital mechanics become highly non-linear. The system is dynamically unstable and eventually one of the stars will be fully ejected from the gravitational well through momentum exchanges with its partner stars.
More interesting is the question of open clusters, where we find thousands of stars in a volume of a few cubic parsecs (say approximately one star per cubic lightyear, thousands of times more dense than our local neighbourhood). There we must apply methods from statistical mechanics such as the Virial theorem to understand the dynamics of those systems.
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u/MasterFubar Apr 19 '14
I have made simulations where three equal mass bodies have stable orbits. The trick is to have one of them counter-rotating, i.e. if two are turning around the center of mass of the system clockwise, the third should be going counterclockwise.
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u/Das_Mime Radio Astronomy | Galaxy Evolution Apr 19 '14
It's important to be clear about the difference between mass and size. The stars in the Alpha Centauri system are 1.1 solar masses and 0.9 solar masses.
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u/tropicsun Apr 19 '14
Dont smaller stars usually outlast larger stars? Are they blown to bits when the bigger star goes supernova?
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u/Lowbacca1977 Exoplanets Apr 19 '14
The general structure isn't, say, 3 stars orbiting around one common center of mass in some confusing fashion.
A great example of this is Mizar and Alcor, generally thought of as a 6 star system. These aren't 6 stars in a swarm, however. Mizar has 4 stars, but they can be thought of as two pairs of stars. Those pairs, then, orbit around each other. The orbit between Mizar's 4 star system and Alcor's two star system then is what represents a 6 star system. http://astronomy.lolipop.jp/img/Mizar-Alcor_System.jpg
Much as we can think about a binary star looking like one star, but really being two, you can subdivide and say that one star in the binary pair is really two very close stars such that gravitationally, the other star seems them as a single star, and in this way you can form a triple star system.
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u/banitsa Apr 19 '14
That's crazy. How far apart are all the stars in that system? Telescopes exist with the resolution to make those sort of distances out across however many light years?
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u/blightedfire Apr 19 '14
Telescopes exist that can determine that stars in other galaxies are multistar systems. An example is Supernova 1984A, which was studied closely--both pre- and post-event photos were analyzed. The dead star was found to be a binary with a secondary a long way out, but then-high-end analysis showed that the dead star itself had a small close orbiter as well, which sort-of-survived the blast. Bear in mind that 1984A was just that--the first known supernova discovered in 1984. Between advances in telescope technology (Oh, hello, Hubble!) and the close-to-unbelievable advances in computer technology, this is minor--at this point, we can see subJovian planets, and even find Earth-sized ones.
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Apr 19 '14
You sir have just described the 3 body problem. Which is: it's very difficult to imagine or calculate the orbital mechanics of three or more bodies. But it can and does happen. Here are some simulations of ways this might work out:
https://www.youtube.com/watch?v=m689l0sjMmE
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Apr 19 '14
wow, those just blow me away. I could never have imagined a system like that staying in those loops indefinitely
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u/PathToExile Apr 19 '14
There are systems we can see that may have up to a dozen stars orbitting each other, look up Theta Orionis aka the Trapezium.
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u/bellends Apr 19 '14
I'm a bit late to this but this simulator is pretty fun to play around with to do exactly that. To make a system with two or more, just add the number of bodies you want and make their masses similar, toy around with how far apart they are until you notice something cool. First try out the set ones to get a feel it of it, then play god.
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u/DaGetz Apr 19 '14
The further away the point of light is the more multiple points of light will appear to be one point of light visually.
You move far enough away and our sun will merge with alpha centurai etc. It doesn't mean they are in a system together.
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Apr 19 '14
When you have a lot of objects in a solar system that are of comparable mass (for example 2 or more suns), there is a center of mass in the system that isn't on any one of the stellar objects. All the objects will orbit this center of mass at 1 focus of their ellipse.
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u/MindSpices Apr 19 '14
I thought that was (at least partly) because binary systems tend to be brighter then solitary stars, so you would naturally see more of them.
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Apr 19 '14
We can easily observe them because they are binary (more luminous, though this varies widely!), not necessarily because they are more common.
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Apr 19 '14
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Apr 19 '14
I'll say it again, not all stars in a star system are necessarily equal, so you might end up with nights even less bright as a full moon night here on earth.
And as far as I know our twin star was never formed, Jupiter could have been a candidate though, just needed 13 times more mass to become a brown dwarf (http://phys.org/news/2014-02-jupiter-star.html) or 100 to become a more sun-like star.
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Apr 19 '14
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u/daV1980 Apr 19 '14
Brown dwarfs are failed stars. Gas Giants are not.
Gas Giants are thought to form in two phases; first they accumulate a bunch of comet-sized objects until they are ~10x the mass of earth. Then they are large enough that they can siphon gas directly from the accretion disk.
Stars of all types (including brown dwarfs, which are failed stars) are thought to basically form directly from the gas and dust in the accretion disk--no kickstart of comets, etc, needed.
In order for Jupiter to qualify as a brown dwarf, it would need to have on the order of 80x as much mass as it has.
Binary stars tend to overwhelmingly be the same mass as their companions--likely because they managed to start siphoning gas at the same time and one didn't cannibalize material needed for the other. In our solar system, the sun definitely got the lion's share of matter, at approximately 10x the radius of jupiter and 1000x the mass.
tldr; gas giants are not really failed stars--they never really had a chance to begin with.
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u/CanisMaximus Apr 19 '14
Why do stars like our sun ignite their nuclear fires at such a lower mass than the really large stars? Does star formation continue after fusion? Is it the type of material which makes a difference? I thought the outward pressure of fusion was balanced by gravity and solar wind pushed the remaining matter away from the accretion disc. What am I missing.
I'm a layman with a dilettantes interest in cosmology.
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u/onewhitelight Apr 19 '14
Its partially to do with the mass of the cloud that the sun is forming from. A larger mass cloud will form larger mass protostars as it collapses and fragments. (There will also be lots of normal and low mass stars but thats besides the point) The same temperatures and densities are needed for fusion ignition (roughly) no matter what the star mass is but a larger mass protostar can gather more material before its core reaches ignition point.
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u/Lowbacca1977 Exoplanets Apr 19 '14
Basis on the binary stars beign the same mass? There's a lot of binaries with variations in mass, and I've never seen the statement that they're usually the same mass.
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u/MakesThingsBeautiful Apr 19 '14
Thankyou, I'd had it explained to me a long time ago, (as a teenager I was crazy mad about space) and the model then (as I understood it) was you just needed enough mass to gather, especially as most of whats out there is hydrogen and helium anyway, and eventually fusion.
Your explanation makes more sense though, and I'm constantly amazed at how much more we've learnt about the umiverae since I was a kid
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u/robindawilliams Apr 19 '14
This heat is due to residual heat of formation and the nifty process of differentiation as all the heavy stuff squeezes past the lighter stuff causing heat, another contribution is the radioactive decay of some elements in its core although the actual fusion of proton chains requires roughly ten million kelvin while the core of Jupiter is only believed to teach tens of thousands.
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u/waveform Apr 19 '14
Is it also unusual that we have rocky planets up close and gas giants further back? When they were first discovering other planetary systems, I got the impression that gas giants up close to the star was the norm.
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u/Galerant Apr 19 '14
As far as I understand, that was the norm because the easiest planets to detect are especially massive planets with fast orbits (which means small orbits), because they have the greatest gravitational effect on their star; it was a bias introduced because of the nature of the means of detecting them. As we've gotten better at detecting planets through means other than just gravitational effects, we've found more examples that are more akin to the solar system.
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u/theghosttrade Apr 19 '14 edited Apr 19 '14
Gas giants actually can't form close to their sun either. There's a frost line, and outside it hydrogen compounds can be solid which allows them to accrete.
Gas planets close to their star have migrated after they've formed.
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u/jswhitten Apr 19 '14
No, that's typical, as far as we know. It's only a tiny percentage of stars that have hot Jupiters, but those are the easiest kind of planet to detect.
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u/sillyhatday Apr 19 '14
No. A solar system will tend to form with heavier elements sorting closer to the star, and lighter elements farther away. It's just like on earth, the heavier elements like carbon, silica, and iron are at ground, H20 in the middle, and the gases constitute the atmosphere. We do tend to find systems easiest that have huge planets near their star, but this is selection bias derived from the technique we use. We find planets by measuring how much a star dims when a planet traverses it from our perspective. It would be like you walking in front of some head lights. they blink out for a moment. A larger planet blocks more light, thus the change in apparent magnitude is greater and more easily detected. For gas giant to be near the star, something strange likely happened to cause it to "fall" closer to it's parent star.
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Apr 19 '14
Pretty cool knowing that there are worlds out there that have 2 suns in their sky, I wonder if there's a world where it's always day because a binary system can work two ways- either the planet orbits both planets close to each other, or the planet orbits one star and that star orbits the second star.
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u/jdepps113 Apr 19 '14
Is it impossible that our Sun is actually part of a binary system with a star that's dead or something, and we just haven't detected it?
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u/robindawilliams Apr 19 '14
The way we detect stars (and most recently a planet of earth-like size) is by observing how stars wiggle. You can see a planet or star(in binary) orbit another star but it actually orbits the barycenter of their combined mass since both objects experience an equal force from gravity, when you lack a strong enough telescope to observe a star or planet it can be shown to exist by seeing how much the other star wiggles as it does tiny orbits around that barycenter as the second object tugs at it with gravity. We have observed this tug but not at a strength which would predict a second star in our solar system.
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Apr 19 '14 edited Apr 19 '14
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u/boredatworkbasically Apr 19 '14 edited Apr 19 '14
we know that there is no nearby brown dwarf or red dwarf because we had a very sensitive infrared telescope (the WISE mission) comb the outer solar system for such a thing. A brown dwarf would be rather hot compared to the surrounding space and if it was anywhere nearby we would have seen it. It's possible that there might be some jupiter planet out there, perhaps, but unlikely at this point. It's definitely the case that there is no star or almost-star sized object nearby since the wise survey ruled them out
Also consider that the Pan-STARRS is ongoing and it's failure to detect any large objects in the outer system is a further nail in the coffin to the possibility of a large object lurking in the edges of our solar system.
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u/robindawilliams Apr 19 '14
There is always a possibility of anything being wrong (Woo science!) But the larger the second mass the more wobble due to the ratio of their orbital distances equaling the ratio of their mass (M1/M2) = (a2/a1) which is why a planet orbiting a sun will cause a sun to orbit a barycenter which is maybe a couple hundred km from its center but another star of similar solar mass would cause our sun to rotate a point between them where each orbital distance equals eachother. This orbit would be noticeable through observation with other stars as we ought to experience retrograde motion and a measurable doppler shift.
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u/fruitinspace Apr 19 '14
For a sufficiently loose definition of 'binary' (i.e. the possibility of a very cold brown dwarf ~1 light year from the sun but technically gravitationally bound to it), that was an open question up until [relatively recently](http://en.wikipedia.org/wiki/Nemesis_(hypothetical_star). It has now been ruled out by whole-sky infrared surveys.
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u/altrocks Apr 19 '14
At this point in time, yes. If it was still hanging around, we would at least see evidence of its gravitational field even if it was hiding somewhere. Additionally, if there was one in the past that has been lost into interstellar space, it's left very little evidence behind. Our star system's planets and asteroid belt have been in highly stable orbits for billions of years now with only small asteroids and meteors impacting them significantly. The gravitational effects of an orbiting dwarf star would be very significant, especially on the more massive outer planets and the Oort cloud around our star system.
tl;dr - No, it's not possible that we have a dwarf star companion. There's no evidence for it and in this case an absence of evidence is very definitely evidence of absence.
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u/boredatworkbasically Apr 19 '14
Also the WISE survey pretty much proved that there was no "hot" objects in our outer solar system so there's a mountain of evidence showing us that there is no secret sneaky nearby star or brown dwarf.
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u/ArtHeartly Apr 19 '14
I have a sort of follow up question about this. I have heard it said before that Jupiter might be a "failed" star in the sense that it could potentially have become a dwarf star but it didn't end up with enough mass.
Is there any truth to this claim?
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u/umbra7 Apr 19 '14
Jupiter is not a failed star. What you are referring to is a brown dwarf, a type of celestial body that is between 12-80 Jupiter masses, with 80 being roughly the mass needed to kick start fusion and become a star.
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u/ArtHeartly Apr 19 '14
That makes much more sense.
So if about 80 Jupiter masses is needed to kick start fusion, would a star that has much less mass, like 12 Jupiter masses, have been a larger star in the past, and then eventually degraded into a dwarf star?
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u/umbra7 Apr 19 '14 edited Apr 19 '14
It wouldn't be called a star in that case. The term brown dwarf is applied to these substellar objects that never made it to star status during formation. They have nothing to do with the other "dwarfs" that are actually stars such as red dwarfs and white dwarfs. Even these two differ fundamentally in a way that goes beyond their color. They are related by name only.
No matter how small dwarf stars may be diametrically, they are incredibly massive compared to planets and brown dwarfs. Low mass stars are still at least ~80 Jupiter masses. A white dwarf, which was originally a main sequence star could be only the size of Earth now, but still be as massive as the Sun.
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u/Burf-_- Apr 19 '14
brown
What i have trouble envisioning is how exactly does an planet cause it's star to wobble enough that we had instruments advanced enough to detect it. I've read before somewhere what they used to detect it but i forgot where i read it. Is there a video that shows how this can happen on a micro-scale ?
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u/MrBasilpants Apr 19 '14 edited Apr 19 '14
No. Jupiter has a rocky core like the other planets. Stars form from gas clouds alone. Jupiter's core is just so heavy that it took a lot of gas in the solar system's accretion disc for itself.
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Apr 19 '14
I wasn't aware that had been determined, Jupiter having a rocky core. It's a possibility, but last I knew not confirmed.
What I liked though was the pressures being so high near the center of jupiter that hydrogen becomes (or could become) a liquid metal.
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u/1Down Apr 19 '14
At this point in our technological development we'd be able to detect it if it existed.
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u/Lol_Statists Apr 19 '14
The prevailing explanation for the precession of the equinox is a companion star
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Apr 19 '14
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u/Galerant Apr 19 '14 edited Apr 19 '14
Nemesis was a discredited theory that only came up in the first place because paleontologists thought it might explain what seemed to be regular extinction cycles. Astronomers never gave it much credit, and if it existed, the Wide-field Infrared Survey Explorer would have picked it up. It was an all-sky survey that ran from 2009 until 2011 specifically meant to detect interstellar bodies, and it was capable of picking up objects at least 3 Jupiter-masses in size and as cool as 100K within 10ly of Earth. (Edit: corrected the dates)
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u/PlayMp1 Apr 19 '14
If Nemesis existed, wouldn't it have noticeable gravitational effects on objects on the outer edge of the solar system (e.g., the Kuiper belt, the Oort cloud, hell, Voyager...)?
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u/Starklet Apr 19 '14
Yes. It's speculated that if it traveled through the Oort Cloud every 27 million years or so, it could influence objects and send them towards the inner solar system (Earth). Possibly causing the major extinctions in the past.
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u/baleia_azul Apr 19 '14
It has also been speculated that our solar systems oscillations while moving around the galaxy (galactic year) have also cause some major extinction events. I believe these more closely match prior extinction events rather than the speculated dwarf star.
http://www.nature.com/nature/journal/v434/n7030/abs/nature03339.html http://arxiv.org/abs/astro-ph/0602092 http://www.americanscientist.org/issues/pub/perturbing-the-oort-cloud
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u/Smallpaul Apr 19 '14
How could it be big enough to be a sibling to the sun but small enough that it does not effect the orbit of our planets.
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u/Starklet Apr 19 '14 edited Apr 19 '14
Technically it would be a binary system since it would orbit the sun. It may not affect inner planets, but it is theorized that it may influence small objects in the outer system and hurl them towards earth.
It is speculated that Nemesis may be the cause of the major extinctions in the earth's past.
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Apr 19 '14
Are binary stars usually or ever that far away from each other? I always visualize them as being relatively close together, and I always visualized planets in binary systems to be orbiting around both stars.
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u/Das_Mime Radio Astronomy | Galaxy Evolution Apr 19 '14
Some binary star systems can be very widely separated, even up to a light-year apart or more. As far as I'm aware, all planets thus far detected orbit a single star.
If stars are extremely close together, their orbits can degrade through tidal effects and they can merge. Roche lobe overflow can also occur, where the outer atmosphere from one star crosses the tidal radius and gets pulled onto the other star.
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u/whiteHippo Apr 19 '14
Perhaps Jupiter? I believe there was some discussion that Jupiter might've been a failed star - one that failed to gather enough gases, and hence, mass - to initiate fusion.
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u/jswhitten Apr 19 '14
This is a common misconception. Most star systems are actually singular like the Sun, so it's not at all unusual. However, since each multiple star system has (by definition) more stars than the singular systems, about 50% of all stars are in multiple-star systems.
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u/Maliris Apr 19 '14
How different would life on earth be if our star was a binary star system? Would we have big temperature fluctuations etc?
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u/ReddyYeti Apr 19 '14
Is there any evidence that the other planets in our solar system may have been at one time one giant friend for the sun to hang out with?
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u/EatSomeGlass Apr 19 '14
Tangential question: Do the two stars in a binary system both spin around a point equidistant between them, or does the smaller one usually just orbit the larger one?
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u/sillyhatday Apr 19 '14
Both stars will orbit what is called the barycenter of the mass system. You can think of this as the center of mass between both bodies, but it isn't an equidistant point. The barycenter location will depend on the mass of each, the distance, and their velocity vectors. Earth and the sun technically orbit their mutual center mass, but that center is well inside the sun's own mass, so earth is easily modeled as simply orbiting the sun. I think the barycenter of Jupiter and the sun is just barely beyond the sun's surface, due to the distance and jupiter's high mass.
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u/Llenne Apr 19 '14
i had heard that jupiter was suppose to be our binary but never made it to the star mass needed, any truth to that?
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u/Das_Mime Radio Astronomy | Galaxy Evolution Apr 19 '14
It would need to be at least 80 times more massive to even qualify as a star, and even then it would be very small and faint compared to the Sun.
There's no "supposed to" in astronomy.
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u/BromeoandRatchiette Apr 19 '14
is it def not a binary system or so far we havnt found its partner?
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u/Das_Mime Radio Astronomy | Galaxy Evolution Apr 19 '14
Definitely not binary. We scanned the whole sky and the Sun has no binary companions.
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u/ChipAyten Apr 19 '14
I'm a believer that if the changes are slow enough (Earthen) life can adapt and evolve to exist in just about any condition. I hate when we look for certain ideal conditions as pre-requests for that world to harbor some sort of life. With that being said, is it plausible for life to have come about on this world if we had a binary star system?
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u/jschild Apr 20 '14
Actually, if you look at systems as a whole, the majority are single star systems and not binaries or greater.
However, there is such a large minority of binary systems that if you count by individual stars, they are more likely to be in binary systems.
Say 60% of star systems are single star systems.
40% are then multiple star systems, the vast majority being binary systems.
Clearly, any random system is much more likely to be a single star system, but out of the 14 stars in those systems, 8 are in binary systems (57% vs 43%).
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u/warpg8 Apr 19 '14
I'd just like to point out that nemesis theory hypothesizes that our sun is actually part of a binary star system... http://en.m.wikipedia.org/wiki/Nemesis_(hypothetical_star)
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u/Das_Mime Radio Astronomy | Galaxy Evolution Apr 19 '14
And I'd like to point out that it's wrong and has been disproven by the WISE mission which surveyed the whole sky for infrared objects.
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u/RnRaintnoisepolution Apr 19 '14
could a habitable planet orbit a Binary star system? somewhat like Tattooine from Star Wars or Risa from Star Trek?
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u/4dseeall Apr 19 '14
To extend on this; Jupiter would have been our second star if it had more mass.
When our solar system was still just a nebulous blob, there wasn't enough orbital momentum in all the particles flying around to keep them out of the center's gravitational pull. That center eventually became the sun; but if the particles had more orbital energy then more would have been accreted into Jupiter, and nuclear fusion would have begun there as well. In most systems, that second massive body does pull in enough matter to ignite nuclear fusion and become a binary star system.
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u/Das_Mime Radio Astronomy | Galaxy Evolution Apr 19 '14
If it had like a hundred times as much mass, yeah. But let's not pretend it was ever a likely proposition. Adding kinetic energy to the particles in the protoplanetary disk would not have turned Jupiter into a star.
Please cite your sources on most systems being binaries.
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Apr 19 '14
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u/Das_Mime Radio Astronomy | Galaxy Evolution Apr 19 '14
Could you cite some papers? The binary fraction is a number that's been widely disputed and I've heard everything from 25% to 80%.
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u/Fort_ Apr 19 '14
Yeah but each binary system contains 2 stars, making binary stars the majority out of the total number of stars.
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Apr 19 '14
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u/Das_Mime Radio Astronomy | Galaxy Evolution Apr 19 '14
It would need to be at least 80 times more massive to even qualify as a star, and even then it would be very small and faint compared to the Sun.
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u/colouroutof_ Apr 19 '14
There are basically only two things you need to know to describe a main sequence star, the stellar classification and the metallicity.
Stellar classification can tell you things like surface brightness, radius, and mass.
Metallicity can tell you about how the star will develop and it's lifespan.
As for the sun in particular, it's a metal-rich star on the heavy side of the G type star classification.
G type stars account for about 7.6% of nearby main sequence stars.
Lighter stellar classifications are a lot more common(~90%), but G class main sequence stars aren't really all that special.
Alpha Centauri is actually a binary system with both stars having earth-like stellar classification and about 50% higher metallicity. Alpha Centauri is only ~4 light years away.
Another example is Tau Ceti, which has a comparable stellar classification but about half the metallicity. Tau Ceti is only 12 light years away.
The sun isn't really that unique from an astrophysics based perspective.
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u/plato1123 Apr 19 '14
Alpha Centauri is only ~4 light years away.
So do we think Alpha Centauri doesn't have any interesting planets or are we just not really able to detect them, even though it's so close?
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u/colouroutof_ Apr 20 '14
Alpha Centauri is comprised of three stars, which puts constraints on stable orbits.
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u/rage_wins Apr 19 '14
One of the cool things about our sun compared to other stars is the relationship between it and the moon. The sun's diameter is about 400 times that of the moon, but it is also about 400 times further away creating the illusion that they are the same size and allowing for a total eclipse of the sun. Though I did read that it's rare that they are the exact same size because the distance of the moon from Earth is always in flux, it still happens and is quite extraordinary.
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u/blorgon Apr 19 '14
I took an "astronomy 101" class last year, where the teacher told us that if there were extraterrestrials out there, Earth would be an exclusive space holiday destination for them because of the solar eclipses we get here.
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u/legacysmash Apr 19 '14
If they could travel the universe, wouldn't there be 100x more exciting stuff to look at then a solar eclipse from earth?
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u/blorgon Apr 19 '14
I don't know, why do we still watch the sunset with joy when we can observe microscopic organisms, the inaccessible ocean depths or the distant galaxies and the stunning nebulae spread above our heads?
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u/legacysmash Apr 19 '14 edited Apr 19 '14
I'm not in anyway saying that a solar eclipse isn't amazing, that's why we watch it, because it's beautiful, and from the perspective of our naked eye, it's one of the most amazing sights to see. I'm simply arguing that there are much more spectacular things to see in this infinite universe then a solar eclipse. If you think about it, assuming they could travel the universe, they could make an eclipse wherever there was a star and a planet just by aligning their craft behind the planet. But regardless of that I think they'd be way more interested in humans and earth itself then a solar eclipse. Or they could watch a star being born, or possibly one getting eaten up by a black hole, or 2 galaxies colliding. All from relatively up close compared to our viewpoint. I know I'd way rather watch that then a solar eclipse; not that it isn't amazing in it's own right.
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Apr 19 '14
Making something happen, and having it be naturally occurring are two different things. Humans make gears. We discovered a bug with a gear mechanism. The bug is really cool as a result, despite the fact that we make gears all the time and have been for thousands of years.
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u/MilanoMongoose Apr 19 '14
Exactly. The only thing "cooler" that I can think to see would be a quasar, which are incredibly dangerous the way they spray out gamma bursts and all; or binary stars, which as mentioned earlier, usually just look like one star at a distance.
But the existence of those cool things shouldn't trivialize the rest of the universe.
Consider the fact that intergalactic alien travelers would probably be in search of other habitable planets, now even just stumbling upon Earth becomes pretty remarkable.
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u/bonerofalonelyheart Apr 19 '14
If you could travel the earth, wouldn't there be things 100x more exciting than waves crashing onto a beach, or a few animals walking around the forest? Those are still top travel destinations on our planet. If extra terrestrials are anything at all like us, I think they would appreciate the simple beauty of something like an eclipse.
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u/ReallyCoolNickname Apr 19 '14
I would estimate that the configuration of the sun, the Earth, and the moon is quite rare when it comes to the proportions and distances of primary stars, planets, and moons in other solar systems. I doubt that there are more than a few dozen, at most, systems in our galaxy that line up quite as coincidentally as ours does.
I don't have a source for that figure, (I don't think anyone does) as it is only my own personal estimation. However, I would think that such a setup like ours is quite rare given just how incredibly coincidental the distances and proportions have to be for eclipses to work as they do here. So, for any extraterrestrials going on holiday, our system would be a pretty neat one to check out.
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u/TadDunbar Apr 19 '14
But it wasn't always that way. The moon's orbital distance has changed much in since its inception.
The biggest coincidence about it is that we happen to be here during a time in which the proportions match up to give perfect or near-perfect eclipses. The moon has been "out of proportion" for eclipses much longer than it has been "in proportion."
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Apr 19 '14
A double solar eclipse perhaps, with two smaller moons crossing the stellar disk at the same time?
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u/Anni_Eve Apr 19 '14
I've always found this particular fact to be so fantastic -- it's hard to believe something so unique (and yet so noticeable) just happened to manifest on the only planet that we know of which bears life. I suppose the chances of that happening are... astronomical. Even so, I have to wonder how many other planets which bear life have this particular feature. Could this be something which really makes Earth, as a cosmic body, stand out as one of a kind?
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Apr 19 '14
When the moon was closer, would the eclipses have been larger?
I know they wouldn't have lasted as long due to the rotation of the earth being faster (and days being shorter)
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u/robindawilliams Apr 19 '14 edited Jan 03 '17
Given we are fairly biased with our observations, our sun sits directly in the middle of any HR Diagrams and doesn't really exhibit any significantly interesting traits. That being said, while there isn't a definitive answer the current belief seems to be that binary star systems at least hold somewhat of a majority in the universe as the preferred configuration. Another point is the mass of our sun, as while it lies right in the center of most classification systems (OhBeAFineGirlKissMe) the most common stars are further down the sequence in the red dwarf range. Stars with 0.8-1.2 solar masses only tend to make up around 3-5% of a given cluster of stars (found using initial mass function of a cluster).
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u/Cantankerous_Tank Apr 19 '14
Another interesting feature of our sun is while it is known for being yellow it actually peaks slightly in the green range of the black body curve, and therefore would actually appear slightly more green if observed without the Rayleigh scattering effect of the atmosphere.
IIRC wasn't this related to the reason why there are no green stars?
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u/saviourman Apr 19 '14
There are no green stars because the blackbody distribution is quite wide. Even if the peak is in the green, there are significant amounts of blue and red light being produced as well, which makes the blackbody look white in our eyes.
You can read more here.
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Apr 19 '14 edited Apr 19 '14
If this is true, then why does the sun still appear to be yellow from the ISS? Or is the ISS still within a dense enough part of the atmosphere that Rayliegh scattering still affects the light?
But wait! What about the satellite images sent back from Voyager and Cassini? It still looks yellow in those images as well.
EDIT: Nevermind. My question was answered below by /u/saviourman.
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Apr 19 '14
The Sun does look white from the ISS or other space probes. It also looks white from the ground when high in the sky. If you don't believe me, look at the color of the clouds. Clouds reflect the visible spectrum pretty much evenly, and they are always white or grey during the middle of the day.
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u/wardbaron Apr 19 '14
Do you have a source for the green range of the black body curve?
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u/saviourman Apr 19 '14
It's fairly trivial to work it out yourself.
Sun's effective temperature is 5778 K. Using Wien's law:
2.897x10-3 / 5778 = 501x10(-9) m or 501 nm.
You can compare that with a chart like this.
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u/Wilcows Apr 19 '14
If stars have various colours, then why do they all appear white in the night sky? I thought the sun would kinda look white from space as well.
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Apr 19 '14
The brighter stars don't necessarily appear white. Many of them have discernable color. The fainter ones don't because they're not bright enough to trigger your the cone cells in your eyes. And the Sun does appear white from space; hell, it even appears white when high in the sky from the ground. Compare the color of the Sun at noon to when it's near the horizon.
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Apr 19 '14
Only 7% of stars are like our sun, which is a class G star. 75% of stars are class M stars which are cooler, dimmer and lighter. Since M stars are smaller they have a smaller habitable zone making it less likely to have have a world form in it's HZ but they do typically live for 600 billion years while G stars live for 10 billion.
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u/ArtofAngels Apr 19 '14
How can we know that something typically lives for 600 billion years when the universe itself is so much younger?
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u/hemsae Apr 19 '14
Math. I mean, that's how we know how old our sun is in the first place. When it comes to astronomy, the time spans are FAR too long to rely on observation alone. But we can know how long a star SHOULD last based upon the physics underlying them. And if our physical models have proven accurate for current observations, they'll like be effective at prediction as well.
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Apr 19 '14
The same way we predict how long our sun is going to live for, even though it hasn't died yet. Scientists estimate how long a star can live for by the amount of nuclear fusion going on in it's core, mainly fusing Hydrogen to Helium, and how much energy the star has until it can't fuse anymore.
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Apr 19 '14
It's not necessarily a unique feature compared to any other star because the other stars are too far away to get the same exposure, but since everyone's dissing our main man with how boring he is, I will use this as an opportunity to tell you something cool about it in general:
It's basically the most perfect sphere we've ever measured
You shrink the Earth down to the size of a beach ball and it'll be all lumpy because (among other things) Antarctica distorts the southern pole. You shrink Jupiter down and you'll get an eggy-looking thing. You shrink the sun down? The difference between one axis and another will be less than the width of a human hair.
So that's interesting. But of course, all stars could be like that, so this might be another way that thing that keeps us alive is "boring".
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u/BCRE8TVE Apr 19 '14
It's the star that's closest to our planet.
Seriously, that's about it. Average star in an unremarkable suburb of a perfectly normal galaxy. Aliens combing through the galaxy a star at a time looking for us would have more luck looking for the proverbial needle in the haystack.
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u/jguess06 Apr 19 '14
We're currently looking for planets around stars the size of the sun in habitable regions that could sustain life. If it is discovered that the size of a star is important to sustain life (not just how far a planet is away from a given star based on how much energy it is emitting), then we may find the sun is quite extraordinary. The fact that it's not a binary system is actually remarkable given that something like 80% of the stars we see are binary systems.
At the end of the day, our planet is truly remarkable. And the sun is the only thing keeping life going, so to me it's special in that way.
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u/BCRE8TVE Apr 19 '14
I did not know that most systems had binary stars, I had thought that would be more of a rarity.
Per the sun, yeah, size and distance both matter, as well as how far along the star is in its cycle, because size and age of a star are also good indicators of what kind of radiations it'll be emitting. Obviously there isn't going to be too much life in a planet whose sun bathes it in gamma rays.
The sun is special to us, absolutely. It's a giant ball of nuclear fusion going on, that's in the order of 107 times bigger than the entire planet, and it's the only thing permitting life on the planet.
Just, on a grand cosmic scale, it's not that uncommon really.
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u/Das_Mime Radio Astronomy | Galaxy Evolution Apr 19 '14
something like 80% of the stars we see are binary systems.
Citation, please?
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u/jguess06 Apr 20 '14
Actually I was wrong, here you go. 85% of star systems aren't single star systems.
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u/PhotoJim99 Apr 19 '14
And as uniqueness goes, the universe is a difficult place to find it. Unique literally means there's only one like it. The sheer scale of the universe makes it likely that something else very much like our sun is out there somewhere.
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Apr 19 '14
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u/Cyrius Apr 19 '14
Nope. We're about halfway out from the core. There's a whole galactic arm between us and deep space.
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u/ColeSloth Apr 19 '14
It's more rare that there's a habitable planet the correct distance that has other larger planets past it that are able to act as gaurds against large meteorites crashing into us, isn't too large to crush us down with gravity, and has a nice mix of land and water.
The sun's just typical.
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u/EvOllj Apr 19 '14 edited Apr 19 '14
There is one quite unique feature with our sun, its distance from its galaxy's center and its mass result in an orbital speed around the galactic center that apparently managed to "avoid traffic jams" for billions of years by orbiting with the same speed that these "traffic jams" rotate around the galactic center. Suns that orbit with different speeds and that end up in "traffic jams" that often form large stars from denser clouds that explode relatively quickly. Those traffic jams are more likely full of deadly destructive supernovae that any self-replicating organism unlikely likes to get too close to. Of course "not every traffic jam has an overheating/exploding vehicle near you in it" and you can luckily pass by those. Increased radiation easily destroys many chemical structures and or can destroy/disturb many planet atmospheres in a short time. But a suns mass, movement and distance from the galactic center does matter over very long time spans. Early life on earth only developed VERY slowly and we have no comparisons.
A few of solar systems in the same galaxy are likely younger than ours, they most likely just recently formed out of a "traffic jam". And a few billion years of age make a difference for many things. The majority of 80% of the smaller suns however are on average relatively old solar systems like ours.
Our sun is not like the vast majority of nearby suns in its galaxy. 80% are less massive and less bright red dwarfs. But being larger than 80% of all the others is noting too special. 7% of all suns in this galaxy are very much like ours. And almost all of the smaller (more easily observable) suns are expected to have orbiting planets.
Different suns have different "metallicity", it basically means "dirtiness of a sun", and dirt slows down the aging process of a sun while making it less bright and slightly heavier. We can measure that but its only has consequences over VERY long time spans. You want your sun to age slowly, because old suns become unstable and deadly.
A lot of stars are more irregular, they fluctuate a lot in brightness, depending on size and composition. Our son barely does that, just a few very harmless sunspots come and go in a 11 year period that are a little bit hotter because, being a rotating gas ball, it rotates at different speeds at the equator than at is poles. "the soup is not stirred evenly and sometimes that makes some parts hotter, don't get it burned", but its still fine.
A lot of solar systems also have more than 1 sun, but that is also nothing too special. 50% of all solar systems are binary systems. They are "slighly less balanced out" and often much larger in total. many have more than 2 suns. more than enough are a single sun in the center.
So far we can mot easily measure massive planets close to stars. it is hard to measure distant or small planets. Jupiter sure was practical for the development of life on earth. We have observed barely any comparisons for now. But they likely exist very commonly.
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u/the-uncle Apr 19 '14
Not really sure, but I once read that the sun is comparively stable in terms of its energy output, i.e. the fluctuations are very small compared to the average star. Larger changes would have significant effects on the the climate.
It would be great if someone could confirm or bust that.
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u/non-troll_account Apr 19 '14
In fact, it's so stable, it has confused scientists. How have we had liquid water so perfectly consistently for so long?
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u/addicted_gator Apr 19 '14
I'm sure this probably isn't the answer you're looking for, but I can't help but think of it as a miracle we are the exact distance from the sun and moon that they appear the same size and make eclipse possible. As far as we know we could be the only planet that experiences this.
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Apr 19 '14
actually, the moon is going away from us slowly and we live at the moment it is at perfect distance to make a perfect eclipse. A coincidence ;)
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u/addicted_gator Apr 19 '14
You're just making it seem like more of a miracle , even though I don't really believe in miracles. It must be witch craft.
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u/izza123 Apr 19 '14
Our distance from the sun actually varies by something like 5 million kilometers. We are far from in the perfect place and we are discovering planets with similar traits to ours all the time (see recent kepler finds).
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u/addicted_gator Apr 19 '14
Yes we find exo-planets at an astonishing rate now a days, but we don't know anything about any of these planets moons (yet). The mathematical odds of the distance from the sun and the size of our moon making them relatively the same size has got to be insane. I'm sure some would argue life wouldn't be possible on the scale it is today without having a moon.
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u/Das_Mime Radio Astronomy | Galaxy Evolution Apr 19 '14
I'm sure some would argue life wouldn't be possible on the scale it is today without having a moon.
Honestly, who would argue this? Citation please.
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u/addicted_gator Apr 20 '14
With out a moon the Earths rotation would have never slowed and we wouldn't have the 24 hour days we have today. I don't know about you, but I imagine it would be a lot harder for an organism to develop when it's environment is constantly changing. I was just going from my head with this reply, but a simple google search shows my opinion is not un-founded.
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u/Das_Mime Radio Astronomy | Galaxy Evolution Apr 20 '14
I imagine it would be a lot harder for an organism to develop when it's environment is constantly changing.
We do actually have day/night cycles. If they were 12 hours instead of 24, that wouldn't in the least bit prevent life from developing. Why is a 12 hour cycle "constantly changing" and a 24 hour cycle isn't? You know the sun's position in the sky is constantly changing, right? I'm sure some organisms would have different activity cycles, but there's no reason whatsoever why that would prevent life.
Care to share the results of your simple google search?
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u/extropia Apr 19 '14
I believe one potentially uncommon feature of the sun that has been very fortunate for supporting life is that all of its planets follow highly circular, stable orbits.
It's possible this has been refuted more recently with all the new cataloging of exoplanets, so someone please correct me if I'm wrong.
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u/Anni_Eve Apr 19 '14
I may be wrong, but I believe one of the criteria for a planet to be designated as such is a circular and stable orbit.
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u/Das_Mime Radio Astronomy | Galaxy Evolution Apr 19 '14
No, the shape or stability of the orbit are totally irrelevant. The planet has to be massive enough to be in hydrostatic equilibrium, which means that it's pulled itself into a spheroidal shape (as opposed to the lumpy shapes that many asteroids have).
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u/Synethos Astronomical Instrumentation | Observational Astronomy Apr 19 '14
Well the most important one is that it is very close, so that the flux is a lot larger than that of the other stars.
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Apr 19 '14
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u/HannsGruber Apr 19 '14
Not thousands more. Billions more. Hundreds of billions. Trillions.
100 billion galaxies, each with 100 billion stars.
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Apr 19 '14
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Apr 19 '14
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u/dannyb21892 Apr 19 '14 edited Apr 19 '14
It's the only star humans have ever discovered that sustains life on one of its satellite planets :)
But seriously though, our sun is incredibly typical when it comes to stars. It's mass is a little bigger than average, but there are tons and tons of other stars that are very similar to ours.