Why does the Milky Way appear to be slanted in the sky?

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I've seen theories as to why the Milky Way stars appear at an angle. When we look up at the sky, the milky way should be seen through the edge straight across, in the lower part of the sky in winter in the northern hemisphere and higher up in the summer. The solar system should be in the same plane as the galaxy. Apparently it's not. Why not?

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