She lets go of my hand and slips off into a dark prayer hall, giving me a wave.

CNN: From Our Correspondent: Far Braver Than I

There's barely time to understand what's happening before a flash of silver whale's skin breaks the surface, dips beneath a wave and plunges down to the dark fathoms of the North Atlantic.

BBC: An Icelandic journey to the centre of the earth

This means that normal matter collapses more slowly than dark matter, and that when it does so it has a tendency to oscillate, generating a sound wave.

ECONOMIST: Astronomy

Millions of people were left in the dark, with no power, no telephones, no internet, and no air-conditioning during the worst heat wave in years.

FORBES: The U.S. enters the 20th century: why we can't keep the electricity on