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View of Milky Way from Earth

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  1. Mar 19, 2007 #1

    PhanthomJay

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    When we view the Milky Way with the naked eye from earth in the winter night sky, we see the streakish 'cloud' of its spiral arms. Are we looking in toward its center toward the inner arms, or out toward its outer arms? And vice versa in summer? I don't recall ever noticing any difference in the appearance of the streak. And we don't see it at all if standing on the north pole?
     
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  3. Mar 19, 2007 #2

    Janus

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    You look towards the center of the galaxy when you look towards The constellation of Sagittarius.
    Dust obscures our vision so we can only see so far as we look along the disk of the Milky Way. So even though more stars lay in the direction of the core, we can't see them, the result is that the Milky Way looks fairly uniform in all directions. (At one time this fooled astronomers into thinking that we sat near the cneter of the Galaxy)
    The way the earth is oriented towards the Milkly Way has it crossing the sky in a more or less North and South direction, so it passes fairly close to the North Star, so yes, you would see it from the North (and South) pole.
     
  4. Mar 19, 2007 #3

    PhanthomJay

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    Thanks, that clears it up, except i have one more question. As viewed then from the equator, then you don't see it hardly at all?
     
  5. Mar 20, 2007 #4

    Janus

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    Remember, the Milky Way makes a complete circle around the Earth that runs in a mostly North-South direction. As such, it can be seen from every part of the Earth.
     
  6. Mar 20, 2007 #5

    PhanthomJay

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    OK, but at the equator, it would be much lower in the sky, correct? I'm having trouble with my 3D image perception.
     
  7. Mar 20, 2007 #6

    russ_watters

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    Different sections of it will be lower the further north you get, but since it is a band that wraps around the entire sky, part of it will go right overhead, depending on time of day/year.

    Think of a line of longitude projected out into space.
     
  8. Mar 22, 2007 #7

    PhanthomJay

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    To think I used to be an astronomy buff. Here's my problem visualizing this: If the earth/sun were at the center of the Milky Way galaxy, then, sure, I can envision a 360 degree circle of its galactic spiral wrapped entirely around the earth. But since we're not in the center, but rather in one of the outer spirally arms, then, when we look in toward the center in the winter, toward an inner spiral, then why should the streak of white wrap around the globe in a 360? It would seem to me that it's a convex shape curving away from us, not around us? Or is it that we're not looking at an inner spiral, but rather, our own??
     
  9. Mar 22, 2007 #8

    russ_watters

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    Here are two graphical representations. Notice on the top-down view that we aren't all the way out at the edge of our spiral arm. So from the side-view, there is milky-way both to the left and the right instead of just to the left (toward the center) http://www.enchantedlearning.com/subjects/astronomy/solarsystem/where.shtml

    Based on this, you'd think the inner part would be much brighter than the outer part, but as Janus said, there is a lot of dust obscuring our view. But even that debris glows, and if our eyes were better, it would be truly spectacular.
     
    Last edited: Mar 22, 2007
  10. Mar 22, 2007 #9

    PhanthomJay

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    Yes, nice view, good explanation, my thanks to you and Janus.
     
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