... Tonight's Sky . ... Observing . ... Sky this Month . ... Is cosmic acceleration changing? A new analysis shows that dark energy, the engine driving the universe's speeding expansion, may be changing fast. ... Cosmic acceleration is the biggest mystery in all of science," says University of Chicago cosmologist Michael Turner. ... for measuring dark-energy changes. ... and any change in dark energy's acceleration ? ... Only registered members of Astronomy.com are allowed to comment on this article. ...