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You may be used to the concept of astronomers taking a spectrum of the light emitted by a star; which can be used to deduce such things as the star's age, its chemical composition and its temperature. Well now Ivan Baldry and Karl Glazebrook at John Hopkins University have combined the light from over 200,000 galaxies, (from within 2 billion light years), to give an 'average' spectrum representative of the entire universe.....

They have calculated how this spectrum would look like to our eyes, taking into account the distance of each source and de-redshifting it. It turns out the colour is nearly, but not quite white, a description the above authors liked is a 'cosmic latte' beige. Although this might all sound like just a bit of wacky science; populistic fluff, it's not just a bit of fun; the colour is indicative of many processes working on a universal scale, such as the average number of each type of star present. Young, hot stars will have a blue colour, whereas old stars will have a red colour (red giants). The combination of these colours gives an average, and tells us that star formation peaked between 1 and 2 million years after the big bang. As the universe ages the its colour will slowly shift to the red end of the spectrum, as its stars age and die, and resources to make new stars dwindles away....

This work can be extended to reveal facts about the average chemical composition of the universe, and the rate of star formation. If further samples of galaxies are taken from restricted distances (and therefore ages) from us, the actual evolution of the universe can be displayed, in a shift of colours.

(Their first press release stated the colour was turquoise, but it turns out that they had made a mistake in their calculation.)

Source :- The New Scientist, 19 January 2002
Further information, http://www.pha.jhu.edu/~kgb/cosspec/color-univ-faq.txt
http://arxiv.org/abs/astro-ph/0110676

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