2.5m Sloan telescope at Apache Point Observatory
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Galaxy survey probes dark energy

Astronomers have measured the precise distance to over a quarter of a million galaxies to gain new insights into a key period in cosmic history.

The 3D map of the sky allows scientists to probe the time six billion years ago when dark energy became the dominant influence on the Universe's expansion.

No-one knows the true nature of this repulsive force, but the exquisite data in the international BOSS survey will help test various theories.

Prof Will Percival from the University of Portsmouth describes how the map was made.