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Spectroscopy: you pass the light through (or reflect from) a dispersive element (a prism or diffraction grating) and then you record the dispersed light. You have a record of the intensity of the light as a function of wavelength. Advantage: potentially you can record the light of one or more objects over a very wide wavelength range and have excellent fine ...


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This is not my field, but I think it is as simple as a combination of the things you said - accurately estimating the amount of "normal matter" within the solar radius, accurately measuring the rotation curve (different tracers can give slightly different results), but mainly that dark matter does not dominate the dynamics at small radii. For instance we ...


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To answer such a question you need to set some parameters. The obvious thing to do is to ask whether, with our current technology, we could detect ourselves at the distances you suggest? The answer is no. You can find some more details in the related question Detectability of interstellar messages In summary, the most powerful radio signals we send into ...


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By estimating the distance is the most obvious method, but you are correct, the parallax will be too small to measure. If we can tell what type of star it is (by measuring its spectrum, or using its colour(s)), then we know roughly how intrinsically luminous the star is. The actual brightness then tells us how far away it is. Fortunately, the diameter of ...



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