“Merlin” (8 p.m., ABC): Banish that image of an old, bearded wizard from your head.

“Merlin” (8 p.m., ABC): Banish that image of an old, bearded wizard from your head. “Merlin” reimagines the medieval adventure and pegs it to a hot, young hunk (Colin Morgan) with magical powers.

“Impact” (9 p.m., ABC): And you thought the economy was our biggest problem. “Impact” is a two-part disaster flick in which the moon comes hurtling toward Earth. David James Elliott, Natasha Henstridge and James Cromwell star.