Eclipse

An eclipse was, according to what Autloc once told Barbara, when the Moon passed before the sun and caused darkness.

Aztec tradition required that during an eclipse, a human sacrifice — indeed, the "Perfect Victim" — be given to the Sun God. (TV: "The Bride of Sacrifice")

In 1794 France, the First Doctor, as part of his plan to escape from a road works overseer, claimed that there would be an eclipse, distracting the overseer long enough for the Doctor to take some money from his purse.

All three suns of the Planet of Light were eclipsed once every three hundred years, resulting in a brief period of darkness which caused the inhabitants to go insane with fear and destroy their civilisation. (COMIC: World Without Night)