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Thread: CWBP 2 : Astrophysics

  1. #11
      Falconius is offline
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    In my mind the extra moon was following the exact same orbital path as the real one, only at a different speed. So it clearly could not be in the same physical reality. What would make it even more interesting is the risk it might have of ever fully manifesting and causing a collision. In that case though we'd have to make pretty clear what exactly causes the fluctuation in the moons reality.

    Or maybe, one moon could be here the other in another dimension and they both fluctuate between the two dimensions but one is more here and belongs here and the other belongs there.

    On the star. I was sort of imagining it like visible disc in the night sky but not much brighter then stars in general. Just more surface area. But if we have i throwing off particle clouds it could obscure a much brighter entity. If the star is as bright as a full moon at night then its obviously going to wash out a lot of other stars, making the study of stars either astronomy or astrology more difficult. Reading the wikipedia, what if the white dwarf was old enough that it wasn't too far from becoming a black dwarf. Or maybe I'm just obsessed with Jack Vance. I guess not every star has to be dying to be interesting.

    Or we could go for a brown dwarf as well but I was wondering if those might be too bright for our purposes. Another possibility is that our planet is orbiting a star that is itself orbiting a different star. As opposed to know where the other star is orbiting ours. Is that possible? Is there any point?
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  2. #12
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    I like most of those ideas.

    Problem is, if we're orbiting star A, and star A is orbiting star B, then ... here how about a really bad picture...

    CWBP 2 : Astrophysics-star.png


    Facts we know:

    Star B has a larger hill sphere (and a stronger gravitational pull than Star A. If it didn't, Star A would not be pulled into orbit.

    At some point in orbit, we would be between Star B and Star A.

    In order for Star A to orbit Star B, Star B must have significantly more MASS. It will be bigger, probably much, much hotter.

    So, when we reach that side of Star A... closest to star B, we would be scorched... All the heat from star A that normally supports life on our planet PLUS a lot more heat from Star B... probably twice what we get from Star A.

    If Star B is not that big, it loses mass, loses it's pull, and Star A doesn't orbit.

    If we move far enough away from Star B (meaning Star A has to move farther away too,) then we move out of range of the hill sphere (not for a planet, but for a star (A) of any significant mass) and Star A doesn't orbit.

    If we're *too* close, or our star is too small/cool, then we get pulled into orbit around star B, instead...

    It CAN be done, and maybe something with that could affect something like what we've discussed with the moons, but it would be VERY complicated. Not saying that's a bad thing, it could be fascinating, but I thought I should at least point it out.
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  3. #13
      Scoopz is offline
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    Heat is a problem, but given that it's 75AU away one night is more like a really bright dusk, there might not even be Ice caps. As far as the planet's orbit, it's good. it's got significantly more attraction to its star than the primary star. However, it'll experience some really crazy gravitational effects. Probably really intense tides. etc.

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    fALCONIUS: a white dwarf is basically a dying star, it does not burn or fuse anything. It's just like the center of the Earth, it does not produce any energy, it's just cooling off.

    The particles I was referring are several billion years old and should have dissipated but it's possible that some parts have agglutinated to form some magnetic clouds or something like that. Yes they could obscure the vision but they are located at specific places.

    I'm trying to find how bright would be a star at around 75 AU. It seems the apparent magnitude of the Sun is around -17 :Apparent magnitude - Wikipedia, the free encyclopedia (It's brighter than a full moon)
    but that's for the Sun and my idea was to have a much smaller star around. A good example of a white dwarf would be Sirius B, the twin of Sirius A, one of the brightest star in the sky. Sirius - Wikipedia, the free encyclopedia
    I have no idea how to calculate the apparent magnitude of our star.


    some illustrative comparisons
    File:Comparison sun seen from planets.svg - Wikipedia, the free encyclopedia
    File:Artist?s impression of the surface of the dwarf planet Makemake.jpg - Wikipedia, the free encyclopedia

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    Having the nearest star orbiting the other star is also possible. The difference in mass can be small. Alpha centauri A and B masses only have 21% of difference. Alpha Centauri - Wikipedia, the free encyclopedia

    If they are far enough from each other, we won't have too many heating/gravitational problems I guess.

  6. #16
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    Mkay. Just random musings... wanted to be sure if it would be a problem. (hadn't bothered to do the math)


    I'm just wondering if the difference in mass (only 21% might still be millions of miles in size?) would affect how much heat hits our planet or howit would affect the orbit
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  7. #17
      Falconius is offline
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    Yeah I was aware the White Dwarf was no longer functional, but they still last effectively forever. There's dead and really dead. I think we should probably just stick with what you had already worked out, I was just musing about different possibilities. I hadn't really read much on the subject before and the possibilities were all pretty interesting.

    I am still concerned about the effect on star gazing. A full moon and something brighter than the full moon would completely wash out a night sky. These effects could be felt possibly for hundreds of years depending on relative locations of the star and planet. Maybe? As far as I can tell one side of the planet would have this orb hanging in the sky for a very long time since the orbit is so long.

    Edit: We could I guess set the apparent magnitude to what ever we wish and then adjust the star to match.
    Last edited by Falconius; 02-13-2014 at 07:35 PM.
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  8. #18
      Azelor is offline
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    Ok let see the apparent magnitude is on a logarithmic scale. Every time the magnitude goes up by one, it mean the star is 2,5 times brighter. So... according to my maths and wikipedia... the apparent magnitude of the Sun is 400 000 times brighter than the full moon.

    absolute magnitude : Sun 4.83 vs Sirius B 11,18
    difference is 6,35 so it's something like 250 or 300 times fainter that the Sun and lets not forget than our star is 75 time further. but that just the absolute magnitude, the apparent magnitude is more important

    the distance between the planet and the old star varies between 74 AU and 76 AU if we assume that the old star's orbit is a perfect circle....
    Brightness varies inversely with the square of the distance

    + 1 magnitude: 2,5 times brighter
    + 5 magnitude= 100 times brighter
    + 10 magnitude = 10 000 times brighter
    + 15 magnitude: 1 000 000
    + 20: 100 000 000
    +25: 10 000 000 000
    ...

    now brightness depend on distance too, so to get the apparent magnitude I need the absolute magnitude (11,1. The distance used for the apparent magnitude is 10 parsecs or 206 260 AU. By using the Inverse square law, the square of 206 260 is 42 543 187 600. I think it means that the star is 42 543 187 600 times brighter with an apparent magnitude of about -16. Your at 1 AU and your about to fall in the star and it's dimer than the Sun as seen from Eris at aphelion ... So it's not very bright.

    But since the planet is at 75 AU, we multiply the distance by 75 and divide the brightness by the square of 75 (5625). Which gives 42 543 187 600/5625= 7 563 233 brighter than the original magnitude (11,1. On the logarithmic scale, it mean a decrease by more than 17 units. 11,18-17,18= (yes, the lower the magnitude, the brighter the star)

    -6 which is the apparent magnitude of the star as seen from the planet when the distance is 75 AU...
    Look at the table to get an idea of it's brightness. Nearly 3 time brighter than Venus and 600 time fainter than the full moon.
    Last edited by Azelor; 02-13-2014 at 09:56 PM.
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  9. #19
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    By comparison, Sirius A, the brightest extra solar star as seen from Earth is about 50-60 times dimer than our old star.


    hum what a headache...
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  10. #20
      Falconius is offline
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    Lol. I'll take your word for it. That apparent brightness sounds very reasonable.

    According to Wikipedia, -6.5 is "The total integrated magnitude of the night sky as seen from Earth." So this star would be very apparent but not annoyingly bright. Although I would have thought the total integrated magnitude of the night sky would have been higher.... Guess because it's on a logarithmic scale maybe?

    So if our extra star is a temperature about 5000-6000 k it would be yellow in appearance? Assuming that our main star ans solar system is similar to Earths then that would mean two yellow stars. I'd actually like to differentiate the colours between them more substantially than that. Say either one level down into orange or into a higher level to white or blue white. This way it would allow for mythical opposition in their associations between the two stars. Personally I prefer a darker colour for the natural threat that would seem to pose to our home star. The apparent colours are different though so I'm not sure if what I'm saying makes actual sense.

    As you mentioned Azelor we should also consider what is around the White Dwarf as a result of its change of state. As far as I understand it it could be pretty much anything from planetary nebulae, to rings of debris, to gas clouds.

    We should also put some thought into the rest of the solar system. What planets and how many are orbiting our sun? Are there any rogue planets on a long or weird orbit due to the influence of the second star? Are there any belts of crap in orbit with us? Etc.

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