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Thread: astrophysics - dumb questions

  1. #11
    tWebber Roy's Avatar
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    Quote Originally Posted by Sparko View Post
    Thanks.

    OK something else I thought of while watching shows about finding exoplanets...

    They detect them by measuring the light dip as a planet passes the star, right?
    Sometimes.

    There are 4 or 5 different methods, of which that's just one.

    So the only planets we can see would be those whose ecliptic lines up with our line of sight, right? If the solar system's ecliptic were 90 degrees from our line of sight (we would be looking at the north or south pole of the star) we would not be able to see if it has planets or not, right?
    By that method, right - it only finds planets that transit the star from our point of view. Other methods (e.g. gravitational lensing of background stars, Doppler measurements) can find planets that don't pass directly between us and their star.

    secondary question, does the ecliptic of all of the stars in the galaxy pretty much line up with ours (maybe because of the galaxy's rotation) or do they vary all over the place?
    They vary. Our own system doesn't line up with the galactic plane, as you can see from the angle of the milky way vs the planets.
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  2. #12
    Must...have...caffeine One Bad Pig's Avatar
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    Quote Originally Posted by TheLurch View Post
    Apparently, the sun is 0.14% by mass iron. It's just a small fraction because the sun has so much other stuff as well. Same thing with Jupiter. The rocky planets have much higher percentages simply because they never
    The vast majority of material in the universe is hydrogen. The sun only has iron in it because the solar system formed from material left over from previous supernovae.
    Minor terminology issue: a nova is different from a supernova. Supernova is the one that involves iron fusion.

    And here, the issue is not the fusion of iron itself, but what that means to the energy balance of the star. A star exists in a balance between gravity wanting to crush it and fusion releasing energy that creates an outward pressure that counteracts that. Fusion of lighter elements produces energy, and as long as that's happening, the star won't collapse, even if some iron's being produced.

    But as your later link indicates, iron probably won't be produced, because it requires especially high energies and pressures, and those don't exist until the star is well on its way to collapse.
    Further, our sun isn't nearly massive enough to produce iron via fusion, and will go out with a whimper (white dwarf) instead of a bang (nova).
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  3. #13
    tWebber Christianbookworm's Avatar
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    Quote Originally Posted by One Bad Pig View Post
    The vast majority of material in the universe is hydrogen. The sun only has iron in it because the solar system formed from material left over from previous supernovae.

    Further, our sun isn't nearly massive enough to produce iron via fusion, and will go out with a whimper (white dwarf) instead of a bang (nova).
    Unless Someone intervenes before then?
    If it weren't for the Resurrection of Jesus, we'd all be in DEEP TROUBLE!

  4. #14
    tWebber Starlight's Avatar
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    Quote Originally Posted by Sparko View Post
    1. If the higher elements are in short supply because of the way they are made during a nova, then why is gold so rare on earth but elements like lead are common?
    Lead is the heaviest element that has a stable form (isotope). What this means is that everything heavier than lead is radioactive and over enough time will break down gradually into lighter elements by spitting out a small piece of itself and thus usually moving in steps of 1 or 2 across the periodic table, but the breakdown stops when it gets to lead (assuming it lands at the stable form of lead) or some nearby slightly lighter element (if it steps over lead or hits the unstable form of lead).

    A second reason is that the creation processes in the star itself will favor some elements over others, because different fusion combinations will require different levels of energy and the amounts of the different lighter elements present will vary. So if there's a lot of carbon around waiting to be fused, you're more likely to get elements weighing Carbon x2 and Carbon x3 etc produced as multiple carbons are fused than you are to get elements that weigh carbon x1.4 etc.

    A third reason is that some elements have more stable forms (isotopes) than others. So there becomes more chance the creation or radioactive decay processes that produce those elements will land on a stable form rather than an unstable one - having double the number of stable forms essentially doubles the target area that the creation/decay process can land on. As you can see from this table of isotopes, about half the stable elements have only 1 or 2 isotopes, and Tin is the winner with 10. Although it's notable that a lot of the elements with a high number of isotopes are quite heavy, so they don't get produced in large quantities because of how the stars work.


    Random side note: This thread reminds me of a 100-year old YEC book I once read at my grandparent's place, one of their arguments for a young earth was that since the sun produced energy via gravitational contraction (they hadn't discovered nuclear fusion at the time of writing, so it was thought that the sun gradually contracted to generate energy) it had to be less than 10,000 years old else it would have used up all its fuel.

  5. Amen Sparko amen'd this post.
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    tWebber Starlight's Avatar
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    Quote Originally Posted by Christianbookworm View Post
    Unless Someone intervenes before then?
    I, for one, demand a supernova.

    Supernova 2020!

  7. #16
    Troll Magnet Sparko's Avatar
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    Quote Originally Posted by Starlight View Post
    Lead is the heaviest element that has a stable form (isotope). What this means is that everything heavier than lead is radioactive and over enough time will break down gradually into lighter elements by spitting out a small piece of itself and thus usually moving in steps of 1 or 2 across the periodic table, but the breakdown stops when it gets to lead (assuming it lands at the stable form of lead) or some nearby slightly lighter element (if it steps over lead or hits the unstable form of lead).

    A second reason is that the creation processes in the star itself will favor some elements over others, because different fusion combinations will require different levels of energy and the amounts of the different lighter elements present will vary. So if there's a lot of carbon around waiting to be fused, you're more likely to get elements weighing Carbon x2 and Carbon x3 etc produced as multiple carbons are fused than you are to get elements that weigh carbon x1.4 etc.

    A third reason is that some elements have more stable forms (isotopes) than others. So there becomes more chance the creation or radioactive decay processes that produce those elements will land on a stable form rather than an unstable one - having double the number of stable forms essentially doubles the target area that the creation/decay process can land on. As you can see from this table of isotopes, about half the stable elements have only 1 or 2 isotopes, and Tin is the winner with 10. Although it's notable that a lot of the elements with a high number of isotopes are quite heavy, so they don't get produced in large quantities because of how the stars work.
    Thanks, that makes sense.


    Random side note: This thread reminds me of a 100-year old YEC book I once read at my grandparent's place, one of their arguments for a young earth was that since the sun produced energy via gravitational contraction (they hadn't discovered nuclear fusion at the time of writing, so it was thought that the sun gradually contracted to generate energy) it had to be less than 10,000 years old else it would have used up all its fuel.
    You HAD to stick in a dig at Christians? really?

    I am not a YEC, by the way. I am pretty agnostic about the genesis time frame, but I believe the universe is 14.5 billion years old.

  8. #17
    tWebber Christianbookworm's Avatar
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    Quote Originally Posted by Starlight View Post
    I, for one, demand a supernova.

    Supernova 2020!
    But it isn't big enough! And we wouldn't survive the explosion. Sad. We wouldn't survive the sun getting hot enough to boil away the oceans either, but that would take longer at least.
    If it weren't for the Resurrection of Jesus, we'd all be in DEEP TROUBLE!

  9. #18
    tWebber Roy's Avatar
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    Quote Originally Posted by Christianbookworm View Post
    But it isn't big enough! And we wouldn't survive the explosion. Sad. We wouldn't survive the sun getting hot enough to boil away the oceans either, but that would take longer at least.
    But would this be better or worse Trump's 2nd term?
    JohnMartin: "My assertions are fact. They are so fact that even when you deny them, you assert them by implication as shown above.
    Hansgeorg: "3 is not a number"
    37818: "What makes you think you are self aware?"
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  10. #19
    Must...have...caffeine One Bad Pig's Avatar
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    Quote Originally Posted by Roy View Post
    But would this be better or worse Trump's 2nd term?
    I'm not sure we talk about Trump enough here. Should all threads lead to Trump?
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  11. #20
    Troll Magnet Sparko's Avatar
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    Quote Originally Posted by Roy View Post
    But would this be better or worse Trump's 2nd term?
    come on guys, don't derail my thread.

  12. Amen Christianbookworm amen'd this post.

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