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Thread: different galaxys, different colours?

  1. #1 different galaxys, different colours? 
    Forum Freshman noob's Avatar
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    Sep 2008

    is it because of different telescope shot, different galaxy gases, authors rainbow fetish, LSD or ......?

    cheers 8)

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  3. #2  
    Moderator Moderator Dishmaster's Avatar
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    Apr 2008
    Heidelberg, Germany
    It's a mixture of many things. First of all, all professional astronomical pictures are a priori without colours. All images only contain greyscales, i.e. numerical values representing the brightness of an object. In order to get a coloured image, one can attribute a colour code to the brightness values in order to increase the contrast or just to produce lovely pictures. Very often, several single images obtained at different wavelengths are sumperimposed, each having a different colour. In this way, colours have actually a physical meaning. When using broadband filters, the colour red is often attributed to larger wavelengths , while blue colours represent smaller wavelengths. When added together, this produces a conversion from red colours to ow temperatures and blue colours to hot temperatures. But there are a couple of physical phenomena that can alter the intrinsic "colour" of objects like quasars: cosmological redshift and extinction.

    Redshift: The redder an object, the higher the redshift the farther away it is.

    Extinction: The redder an object, the higher the extinction. This means that the light has travelled through a large amount of interstellar gas and dust. Just like the red sunset, a star or a galaxy appears redder than it actually is.

    The result is therefore always a combination of all of these influences.

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