- noctilucent cloud
[noctilucent cloud 词源字典]
- "A luminous cloud of a kind occasionally seen at night in summer in high latitudes, at the altitude of the mesopause", Late 19th century: from Latin nox, noct- 'night' + lucere 'to shine' + -ent.[noctilucent cloud etymology, noctilucent cloud origin, 英语词源]