BBC News - Survey gets a grip on dark energy: "What we've done is measure the 3D positions for just over 250,000 galaxies, covering the largest volume of the Universe ever surveyed. That gives us an amazing map that we can then analyse to try to understand how and why the Universe's expansion is accelerating..."
One concerns so-called baryon acoustic oscillations. These are pressure-driven waves that passed through the very early Universe and which were imprinted on the distribution of matter once conditions had cooled below a certain point.
Today, these "wiggles" show themselves as a preferred scale in the separation of galaxies and can be used as a kind of standard ruler to measure the geometry of the cosmos...
The other technique being used by BOSS involves "redshift space distortions". These describe the component in the velocity of galaxies that stems from the growth of structure in the Universe. The team can see if neighbouring galaxies are clustering in the way that would be expected from the action of gravity.