noctilucent (adj.)

"shining by night," as the eyes of a cat or certain high clouds seen in northern latitudes, 1812, from Latin noct-, stem of nox "night" (see noct-) + lucentem (nominative lucens), present participle of lucere "to shine, glow, be bright," from PIE root *leuk- "light, brightness." The word was originally used of tiny sea creatures, by contemporary observers reported to be nereids, but that identification is now considered doubtful.

These are the animals that illuminate the sea, like glow-worms, but with brighter splendor. I have at night, in rowing, seen the whole element as if on fire round me; every oar spangled with them; and the water burnt with more than ordinary brightness. I have taken up some of the water in a bucket, seen them for a short space illuminate it; but when I came to search for them their extreme smallness eluded my examination. [Thomas Pennant, "British Zoology," London, 1812]