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Astronomy term of the day Dark Matter

Dark matter is the term to describe unseen matter in the universe, because it doesn't emit any radiation. Also the calculated movement of galaxies, galaxy clusters and stars are faster than expected. As it is inferred to exist at this time, as there is no way to test for it. I'm sure there is speculation as to its composition.

Further reading.
http://chandra.harvard.edu/xray_astro/dark_matter/index3.html#amount
http://chandra.harvard.edu/xray_astro/dark_matter/index2.html
http://chandra.harvard.edu/xray_astro/dark_matter/index4.html

Video.
Detecting Dark Matter
Minute Physics: What is Dark Matter?
What is dark energy? More is unknown than is known — we know how much there is, and we know some of its properties; other than that, dark energy is a mystery — but an important one. Roughly 70% of the...
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