An unseen telepathic species whose ship is trapped on the far side of a Tyken's Rift, and whose attempts to call for help rob the crews of the Brattain and the Enterprise-D of dreams.
These aliens are never seen or named. They communicate by telepathy and, caught in a Tyken's Rift that drains all usable energy, they send a repeated message to any ship on the other side in the hope of arranging a joint escape. The signal acts on the same frequencies as rapid eye movement sleep, so most humanoids who receive it simply stop dreaming.
They figure in the Next Generation episode Night Terrors. The crew of the USS Brattain go mad and kill one another, leaving only a catatonic Betazoid, and the Enterprise crew soon begin to hallucinate and lose their tempers in the same way.
Troi, who can still dream, keeps hearing the phrase about eyes in the dark and one moon circling. Data recognises a description of the hydrogen atom. The Enterprise releases hydrogen, the aliens supply the other ingredient, and the explosion frees both ships.