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Q about the Sun and the Earth

  1. Apr 23, 2007 #1
    I have three questions.

    1. Why are galaxies disk shaped and not spherical?

    2. Theoretically speaking, if there were a hollow sphere at the exact center of the Earth and you were in it then what would you feel from a gravitational point of view? Would you hover and be able to bounce from wall to wall of the sphere as if in zero G as you were pulled in all directions by gravity?

    3. A: I saw a documentary about the Sun recently. It said that the sun uses five milion tons of hydrogen per second. I think it converts it in fusion with soemthing else and exess energy is given off. How much space would that amount take up. A swimming pool, a small lake?
    B: The sun is a delicate balance between the force of gravity crushing inward and the force of the fusion raction blasting outward. How does this fusion force work. Is it like a hydrogen bomb. That's splitting the hydrogenatom isn't it? But fusion just gives off excess energy. Does it radiate out as a shock wave or is it just heat/light.
    C: What substance is between the surface of the sun and the core which is super dense? I guess it's more hydrogen, is that stuff just wating its turn to be sucked in so it can too be fused for the reaction?
    D: I used to simplistically think of the sun as a massive globule of flamable liquid floating in space with only the surface burning like when they set fire to a liquer drink in a restraunt. I thought that the sun was so huge that it took billions of years to burn off just as it can take a long time for an iceberg to melt if it was towed to a hot area. If the heat and power of the sun comes to us from its core then why is the surface on fire? What is burning, is hydrogen flamable and if so why doesnt the whole lot go up.
    Last edited: Apr 23, 2007
  2. jcsd
  3. Apr 23, 2007 #2


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    because the primordial ooze that was all of the matter that makes up the galaxy, had a "little" turbulance left over from the big bang which was a swirl or vortex or however you want to visualize it. (you know, the little swirls you might observe in a cloud of dust and smoke left behind a high speed moving vehicle.) going around the axis, the "centrifugal force" (i know that's a fictitious force, it's centripetal acceleration) sorta counters most of the gravity pulling all that stuff to the center of mass, but in the direction in line with the axis of rotation there is no cetrifugal force keeping that matter from just collapsing like a pancake.

    all of the Earth's gravitational forces would cancel and you would be weightless (and toasty, it's pretty hot down there which is why that's where they put Hel l )

    certainly more than a swimming pool. dunno how big a small lake is.

    the sun (and the other stars) is like one big H-bomb whose fireball hasn't burned out yet.

    no, it's fusing it into Helium.

    hydrogen gas is flammable (as in the Hindenburg or Rush Limbaugh, both are flaming Nazi gasbags), but that is not the kind of burning going on in the sun. it's a ridiculously big nuclear reaction going on in the Sun. so big that the volume to surface area ratio of the Sun is very big. the rate of consumption of hydrogen fuel has something to do with the surface area and the size of store of fuel is proportional to the volume. it's so big that, even though it is consuming zillions of tons of fuel per second, it will burn for another few billion years before running out of fuel (and then some other nasty stuff will happen).
  4. Apr 23, 2007 #3


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    For your questions on the sun, fusion is different than splitting a hydrogen atom. Its the exact opposite in fact. Simplistically, fusion is when two different atoms are joined together to make a bigger atom. The energy released is much greater than that released in fission, or the splitting of the atom. The sun fuses hydrogen atoms together to produce its energy.

    Hydrogen is flammable but this is not the cause of the energy release from the sun. "Burning" in the name of the process by which something reacts with oxygen, a chemical reaction. The reaction in the sun between two hydrogen atoms is a nuclear reaction, not a chemical reaction with oxygen, so technically, the hydrogen in the in the sun is not "burned."
  5. Apr 23, 2007 #4
    Not all galaxies are disk shaped. The largest galaxies out there are actually ellipsoidal; and, there are smaller galaxies that are either spheroidal or irregular in shape. Take a look at this picture:

    http://upload.wikimedia.org/wikipedia/en/4/4f/HUDF.jpg [Broken]
    (warning: big file)

    This is from the Hubble Ultra Deep Field. All but six (or so) of the objects in this image are galaxies. Many of them are spirals; but, you can also see quite a few that just look like a fuzzy ellipse. And, these galaxies are all far enough away that we can only see particularly large ones; so, you're not too likely to find any either of the dwarf types.

    That depends rather strongly on the pressure and temperature the hydrogen is stored at. Are you asking what volume that takes up in the sun or what volume it would take up at room temperature and atmospheric pressure on Earth?

    The fusion reaction gives off positrons, neutrinos, and a heck of a lot of photons (light). The positrons annihilate with electrons, creating even more photons. As the photons fly outward from the core, they collide with the material making up the outer layers of the sun. Since the photons originate at the core, the force on the sun is preferentially outward. So, this is what opposes gravity.

    Most of the material in the sun is hydrogen; and the farther you get out from the core, the less there is of anything else. This hydrogen will never get "sucked" into the core (although it does swirl around a lot, particularly due to convection), as this would require the core to expel the heavier atoms that are created there. What will happen, though, is that, over billions of years, the region in which fusion takes place will slowly expand and reach some of the material that is not yet close enough to the core to fuse. However, the vast majority of the hydrogen in the sun will never fuse into helium, but will be blown off into space during the final phases of the sun's lifecycle.

    The sun really isn't burning. As others have said, all the energy released comes from the fusion reactions at the core. We see the whole sun glowing simply because it's hot, just like metals glow when they've been heated in a forge.
    Last edited by a moderator: May 2, 2017
  6. Apr 23, 2007 #5


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    Sidenote: I have to say this is one of the most ... novel ... applications of the term "primordial ooze" I've ever come across.

    "Primordial ooze", though arguably not a scientifically technical term, has always been used to describe the hydrocarbon-filled oceans of pre-life Earth. I've never before heard it used in any astronomical or cosmological context.
  7. Apr 23, 2007 #6


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    All other things aside, combustion of hydrogen requires oxygen - of which there is no appreciable amount in the Sun.

    Or on Jupiter, which also is largely hydrogen. My high school friend used to say he dreamed of one day tossing a match at Jupiter. Being the geek I was, I used to point out that it would do nothing.
  8. Apr 24, 2007 #7


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    This leads me to wonder about yet another thing: Why are there galaxies?

    What are the odds that random clumps of mass in space will come together and instead of fuse together into a huge mega "galaxy-star", turn into a spiraling cluster of stars. Is this likely, or are there other hidden forces at work. It seems that at smaller levels, i.e. for stars, we don't get mini star-dust lumps spiraling around each other, but stars.
  9. Apr 24, 2007 #8


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    i knew it wasn't the perfect metaphor. it's primordial and amorphous. "primordial smog", maybe?
  10. Apr 24, 2007 #9


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    because of gravity? because of non-homogeneity? because in the primordial turbulance, there are "little" swirls that become solar systems or star-bearing nebulae (like the Eagle nebula) and bigger swirls that become galaxies?

    i dunno, i wasn't around back then.
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