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Thread: The Astronomy Thread

  1. #41
    conon394's Avatar hoi polloi
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    Default Re: The Astronomy Thread

    Enjoyable news and who says scientists and engineers can't be a perhaps a little superstitious - they attached a little bit of fabric from the Wright brother's plane to it.
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  2. #42
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    Default Re: The Astronomy Thread

    I don't think it's about superstition at all, Conon, I think it's about being aware that we are all standing on the shoulders of those who came before us. If not for the accomplishments of the Wright Brothers we might not have been able to accomplish what we are today. Paying homage to our predecessors isn't superstition imo.

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  3. #43
    conon394's Avatar hoi polloi
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    Default Re: The Astronomy Thread

    Quote Originally Posted by Akar View Post
    I don't think it's about superstition at all, Conon, I think it's about being aware that we are all standing on the shoulders of those who came before us. If not for the accomplishments of the Wright Brothers we might not have been able to accomplish what we are today. Paying homage to our predecessors isn't superstition imo.
    Most likely but it never hurts have a lucky charm either - I did mean it half in Jest. Really Akar did you do programming because if you admit your first program was not hello world everyone around might just edge away. Although they may stop making signs against evil if you add but I did the C/F temp conversion program instead.
    Last edited by conon394; April 19, 2021 at 02:31 PM.
    IN PATROCINIVM SVB Dromikaites

    'One day when I fly with my hands - up down the sky, like a bird'

    But if the cause be not good, the king himself hath a heavy reckoning to make, when all those legs and arms and heads, chopped off in battle, shall join together at the latter day and cry all 'We died at such a place; some swearing, some crying for surgeon, some upon their wives left poor behind them, some upon the debts they owe, some upon their children rawly left.

    Hyperides of Athens: We know, replied he, that Antipater is good, but we (the Demos of Athens) have no need of a master at present, even a good one.

  4. #44

    Default Re: The Astronomy Thread

    Quote Originally Posted by Flinn View Post
    Since it was mentioned here, I guess it makes sense to share these videos about Ingenuity's first flight
    Having spent one's childhood at a time when wireless telephones were science fiction, it is quite impressive that we can now have a drone flying in the atmosphere of Mars.

    An unrelated thing that I was previously unaware of is that Cruithne seems to be orbiting Earth from a strictly terrestrial point of view, although both of course really orbit the Sun.

    https://twitter.com/i/status/1380967913604194307
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  5. #45
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    Default Re: The Astronomy Thread

    oh well I read about Cruithne not long ago, it's interesting how the perspective often does not comply with the reality, in astronomy I mean, we believed that the sun was orbiting the Earth, didn't we?

    However, I've been reading and watching quite much about "orbits" recently, and it's a fascinating argument, in particular when it comes to interaction and gravity effects. For instance it's interesting to know that Jupiter and Saturn are orbiting on a 1:2 ratio (or 2:1, it's the same!), basically by the time Saturn makes 1 full orbit, Jupiter makes 2. That means that they are in orbital resonance and to achieve that stability they had to migrate from and to their actual position during the evolution of the solar system. Recently I watched a documentary about how all the gas giants have first migrated towards the sun and then later on far from it (I'm not going into details now, the theory says that they were slowed down by the presence of gases, which were later dissipated by the increasing Sun wind; however they used it to explain the Late Heavy Bombardment), and that during this process Jupiter and Saturn entered in orbital resonance. Something similar happened with Neptune and many of the Kuiper belt objects, as seen below (my bad I could only find the image with Italian text in it, but it's pretty self explanatory anyways).



    If we really want to dig into the theory, it says that both Uranus and Neptune did not form where they are now, but possibly much closer to the sun (this due to the supposed lack of gases in their actual position) and later on migrated outwards, especially after Jupiter and Saturn got to their 1:2 resonance.. however, once Neptune migrated it scattered the orbits of all the Kuiper belt object, many of which were sent towards the inner solar system (and here you have the Late Heavy Bombardment), all the others set on various orbital resonances with Neptune (as shown by the pic above); mind you, this is a very rough explanation of the theory.

    However, it's interesting to know that orbital resonance does occur with moons as well, Io-Europa-Ganymede are orbiting Jupiter on a 1:2:4 resonance, as shown below



    that quite certainly means that they accumulated or lost angular momentum and speed, during their existence, due to the effects of Jupiter's gravity, until they found this stability.

    On the matter of moons' orbits, it's also interesting to distinguish between a Planet-moon relation and a double planet system: if we look at the Earth-Moon system, we can barely say that its not a double planet system, this because of the arbitrary definition we humans gave of it: all the objects that orbit one around the other influence each other (even the sun, despite having 99,9 % of the total mass of our system, is influenced, in minimum terms, by the masses of all the other objects in the system; this is also a method used to spot extrasolar planets, due to their orbital influence on their own stars), and they have a center-of-mass that they share, around which both orbit; if this point (aka barycenter) lays within one of the two bodies, then the other one is orbiting the one who has the barycenter inside: that's the case of the Earth-Moon system, it lays inside the Earth, but not for much. On the contrary, the Pluto-Charon system is actually a "double planet", since the barycenter lays outside of the bigger body (Pluto)



    Now, think of the reciprocal influence of all the bodies we have in our solar system.... amazing, stuff for quantum computers exclusively.
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  6. #46

    Default Re: The Astronomy Thread

    Quote Originally Posted by Flinn View Post
    On the matter of moons' orbits, it's also interesting to distinguish between a Planet-moon relation and a double planet system: if we look at the Earth-Moon system, we can barely say that its not a double planet system, this because of the arbitrary definition we humans gave of it: all the objects that orbit one around the other influence each other (even the sun, despite having 99,9 % of the total mass of our system, is influenced, in minimum terms, by the masses of all the other objects in the system; this is also a method used to spot extrasolar planets, due to their orbital influence on their own stars), and they have a center-of-mass that they share, around which both orbit; if this point (aka barycenter) lays within one of the two bodies, then the other one is orbiting the one who has the barycenter inside: that's the case of the Earth-Moon system, it lays inside the Earth, but not for much. On the contrary, the Pluto-Charon system is actually a "double planet", since the barycenter lays outside of the bigger body (Pluto)
    Really interesting discussion on not only possible double planet systems but especially the arbitrary definitions (dwarf planets anyone?) that us humans assign to things. I never even considered the double planet interpretation, regardless of how fascinating I have found the relationship between Pluto and Charon. So if Pluto had the exact same mass but it was a sufficiently large gas planet for the barycenter to stay barely within the extent of the center of Charon's orbit, it would be called a regular planet (I am not a fan of the dwarf planet designation) with a moon? Another way to look at it would be that Charon is clearly orbiting Pluto but Pluto is not orbiting Charon. By that criterion, I would call Charon a moon no matter if the tail was wagging the dog to the extent of the barycenter falling outside the sphere of Pluto.
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  7. #47
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    Default Re: The Astronomy Thread

    I always prefer the simple statement that in the absence or neglibility of other gravitational influences the movement of two given masses (with nonzero angular momentum relative to each other*) is most elegantly described** as both orbiting their common centre of mass. Holds for every case and does not require arbitrary classifications of moons, dwarf/pseudo planets, planets, stars, etc.

    *If there is no angular momentum, the two masses will just collide in their centre of mass, but there almost always is some angular momentum.

    ** One can always choose a different frame of reference in which the movement no longer looks like orbiting, but the relative positions remain the same of course.***

    *** In fact this means that strictly speaking "the earth orbits the sun" is just as "true" as "the sun orbits the earth". Its just that in the former case the equations describing the movements of the other bodies in the solar system look more elegant than in the latter (Tycho Brahe, anyone?)
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  8. #48
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    Default Re: The Astronomy Thread

    Quote Originally Posted by Septentrionalis View Post
    Really interesting discussion on not only possible double planet systems but especially the arbitrary definitions (dwarf planets anyone?) that us humans assign to things. I never even considered the double planet interpretation, regardless of how fascinating I have found the relationship between Pluto and Charon. So if Pluto had the exact same mass but it was a sufficiently large gas planet for the barycenter to stay barely within the extent of the center of Charon's orbit, it would be called a regular planet (I am not a fan of the dwarf planet designation) with a moon? Another way to look at it would be that Charon is clearly orbiting Pluto but Pluto is not orbiting Charon. By that criterion, I would call Charon a moon no matter if the tail was wagging the dog to the extent of the barycenter falling outside the sphere of Pluto.
    Good point, I guess much depends on single cases, and considering how variable (infinite variables, actually) the Universe is, every single definition or axiom or whatever is subject to personal interpretation.

    Quote Originally Posted by Iskar View Post
    I always prefer the simple statement that in the absence or neglibility of other gravitational influences the movement of two given masses (with nonzero angular momentum relative to each other*) is most elegantly described** as both orbiting their common centre of mass. Holds for every case and does not require arbitrary classifications of moons, dwarf/pseudo planets, planets, stars, etc.

    *If there is no angular momentum, the two masses will just collide in their centre of mass, but there almost always is some angular momentum.

    ** One can always choose a different frame of reference in which the movement no longer looks like orbiting, but the relative positions remain the same of course.***

    *** In fact this means that strictly speaking "the earth orbits the sun" is just as "true" as "the sun orbits the earth". Its just that in the former case the equations describing the movements of the other bodies in the solar system look more elegant than in the latter (Tycho Brahe, anyone?)
    It's all so complex and interconnected, only very advanced computing will be able to tell us what rules on what, in some thousands of year probably

    I like what Dante said, to cut it short: "L'amor che muove il sole, e l'altre stelle".
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  9. #49
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    Default Re: The Astronomy Thread

    Quote Originally Posted by Flinn View Post
    Good point, I guess much depends on single cases, and considering how variable (infinite variables, actually) the Universe is, every single definition or axiom or whatever is subject to personal interpretation.
    Many-Body-Problems are indeed very hard to calculate and it gets even worse when considering general relativity, where we have been able to obtain analytical solutions of Einstein's equations only for the simplest of settings (like Schwarzschildt), but the general wording of what happens is still very elegant there: All masses contribute to the energy momentum tensor, which determines the shape of spacetime, on which all masses (in the absence of other forces than gravity) in turn move on the straightest possible lines.
    "Non i titoli illustrano gli uomini, ma gli uomini i titoli." - Niccolo Machiavelli, Discorsi
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  10. #50
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    Default Re: The Astronomy Thread

    A pair of orbiting black holes millions of times the Sun’s mass perform a hypnotic dance in this NASA visualization. The movie traces how the black holes distort and redirect light emanating from the maelstrom of hot gas – called an accretion disk – that surrounds each one.


    Here you can find original Nasa's article

    Fascinating, to say the least
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  11. #51
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    Default Re: The Astronomy Thread

    The movie traces how the black holes distort and redirect light emanating from the maelstrom of hot gas
    I'd even say that the black holes do not distort the light - they distort the space(time) in which the light is propagating. The light still takes the straightest line possible in the curved geometry around the black holes.
    "Non i titoli illustrano gli uomini, ma gli uomini i titoli." - Niccolo Machiavelli, Discorsi
    "Du musst die Sterne und den Mond enthaupten, und am besten auch den Zar. Die Gestirne werden sich behaupten, aber wahrscheinlich nicht der Zar." - Einstürzende Neubauten, Weil, Weil, Weil

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  12. #52

    Default Re: The Astronomy Thread

    Quote Originally Posted by Iskar View Post
    ** One can always choose a different frame of reference in which the movement no longer looks like orbiting, but the relative positions remain the same of course.***

    *** In fact this means that strictly speaking "the earth orbits the sun" is just as "true" as "the sun orbits the earth". Its just that in the former case the equations describing the movements of the other bodies in the solar system look more elegant than in the latter (Tycho Brahe, anyone?)
    I would also like to point out (you know this, of course) that this kind of relativity is only illusionary when we inspect astronomical bodies. The relevant vantage point in astronomy is always from outside the system that is being inspected. Looking from outside the Solar system, there is no doubt that Earth orbits the sun. And looking from outside the Milky Way, Sun orbits the galactic center.
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  13. #53
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    Default Re: The Astronomy Thread

    Quote Originally Posted by Septentrionalis View Post
    I would also like to point out (you know this, of course) that this kind of relativity is only illusionary when we inspect astronomical bodies. The relevant vantage point in astronomy is always from outside the system that is being inspected. Looking from outside the Solar system, there is no doubt that Earth orbits the sun. And looking from outside the Milky Way, Sun orbits the galactic center.
    Yes and no.
    In terms of the mathematical models the relativity is very much real and not just illusionary. The change from a geocentric to a heliocentric picture is just a coordinate transformation, as long as you faithfully describe the movements of all bodies in the system (which excludes the actual ptolemaic system where the planets were supposed to orbit earth as well). Of course the equations look much uglier in the geocentric model, which is why we prefer the heliocentric (or more precisely: barycentric) one.
    In terms of the mental images our theories produce I fully agree, that the relevant view is from the outside with all bodies orbiting the barycentre.
    Funnily, in terms of raw observational data one has to acknowledge that the vast majority of our measurements are necessarily geocentric and as such exist primarily as sets of geocentric celestial (2D!) coordinates, maybe with some added estimates on the third, distance, dimension based on parallax or luminosity measurements. The powerful computations transforming these geocentric data into a barycentric model of our solar system are often underrated - in particular if you consider that Kepler did these transformations based on wholly non-digital data without any computational help in the 17th century.
    Feeding lots of data to a computer and letting it spit out some nice plots after a few seconds is one thing we can all accomplish, but just having raw, geocentric data and seeing the barycentric ellipses hidden in these - that's the real deal and probably a level of mathematical intuition none of us will ever reach.
    "Non i titoli illustrano gli uomini, ma gli uomini i titoli." - Niccolo Machiavelli, Discorsi
    "Du musst die Sterne und den Mond enthaupten, und am besten auch den Zar. Die Gestirne werden sich behaupten, aber wahrscheinlich nicht der Zar." - Einstürzende Neubauten, Weil, Weil, Weil

    On an eternal crusade for reason, logics, catholicism and chocolate. Mostly chocolate, though.

    I can heartily recommend the Italian Wars mod by Aneirin.
    Under the patronage of the impeccable Aikanár, alongside Aneirin. Humble patron of Cyclops, Frunk and Abdülmecid I.

  14. #54

    Default Re: The Astronomy Thread

    Yes, it is a an extremely complex process to calculate cosmic distances and positions from our fixed observation post here on Earth with all its limitations. I have a lot of respect for the astronomers and astrophysicists who have developed models and observational methods. The precision of the radial-velocity method in detecting exoplanets, for instance, is nothing short of miraculous to a layman such as me. Scientifically literate or not.
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  15. #55

    Default Re: The Astronomy Thread

    This probably falls more in the area of philosophy of science than astronomy, but has anyone else here questioned the notion of the Fermi paradox (https://en.wikipedia.org/wiki/Fermi_paradox)?

    I have a really hard time acknowledging that any paradox exists. Given the difficulties in interstellar travel (I hold a view that those difficulties are insurmountable, although others disagree), in my opinion there is no reason to assume that we would have been visited or observed by other civilizations even if the universe was teeming with life. We have been transmitting signals for some time, but those signals have not yet reached very far. On a cosmic scale, the earliest signals sent are still within the local neighborhood. I also give some credence to the pessimistic view that technological civilizations are likely to destroy themselves. If we are already causing some sort of climate catastrophy before putting a person on Mars, it may well be that civilizations simply cannot reach a point in which they could have interactions with other civilizations before their natural resources are spent or their living conditions have been ruined.
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